7.3.1 Output Voltage Setting

The converter output voltage is set in a way that is similar to a traditional analog controller, by using a voltage divider from the output to the feedback (FB) pin. The output voltage must be divided down to the nominal reference voltage of 600 mV. Figure 17 shows the typical connections for the device. Using the unity gain differential voltage sense amplifier, the TPS40400 can regulate the voltage directly at the load. This method provides better load regulation for output voltages lower than 5-V nominal (see Electrical Characteristics table for the maximum output voltage of the differential sense amplifier). For output voltages above this level, connect the output voltage directly to the junction of the R1 resistor and the C1 capacitor, leave DIFFO open, and do not connect the VSNS inputs to the output voltage. In this case, it is also recommended to connect the VSNS+ pin to the BP3 pin and the VSNS– pin to GND. The differential amplifier may also be used as a voltage buffer, provided the electrical specifications are not exceeded

Figure 17. Setting the Output Voltage

The components in Figure 17 that determine the nominal output voltage are R1 and R2. R1 is normally chosen to ensure that the feedback compensation values (R3, R4, C1, C2 and C3) are close to readily available standard values. R2 is then calculated in Equation 1.

Equation 1.

where

• V_FB is the feedback voltage
• V_OUT is the desired output voltage
• R1 and R2 are in the same units

The feedback voltage can be changed ±25% from the nominal 600 mV using PMBus commands, allowing the output voltage to vary by the same percentage. See Output Voltage Adjustment for further details. After setting the output voltage is set and calculating the values of R1 and R2, calculate the VOUT_SCALE LOOP parameter. The PMBus interface requires this parameter in order to properly adjust the output voltage.

7.3.2 Input Voltage Feedforward

Input voltage feedforward functionality maintains a constant power stage gain as input voltage varies, and provides for very good response to input voltage transient disturbances. The simple constant power stage gain of the device greatly simplifies feedback loop design because loop characteristics remains constant as the input voltage changes, unlike a buck converter without voltage feedforward. For modeling purposes, the gain from the COMP pin to the average voltage at the input of the L-C filter is 6 V/V.

7.3.3 Output Current Limit and Warning

The TPS40400 device uses a differential current sense scheme to sense the output current. The sense element can be either the series resistance of the power stage filter inductor or a separate current sense resistor. When using the inductor series resistance as in Figure 18, a filter must be used to remove the large AC component of voltage across the inductor and leave only the component of the voltage that appears across the resistance of the inductor. The values of R5 and C4 for the ideal case can be found by Equation 2. The time constant of the R-C filter should be equal to or greater than the time constant of the inductor itself. If the time constants are equal, the voltage appearing across C4 is be the current in the inductor multiplied the inductor resistance. The inductor ripple current is reflected in the voltage across C4 accurately in this case and there is no reason to have a shorter R-C time constant. The time constant of the R-C filter can be made longer than the inductor time constant because this is a voltage mode controller and the current sensing is done for overcurrent detection and output current reporting only. Extending the R-C filter time constant beyond the inductor time constant lowers the AC ripple component of voltage present at the ISNS pins of the device but leaves the correct DC current information intact. This also delays slightly the response to an overcurrent event, but reduces noise in the system leading to cleaner overcurrent performance and current reporting data over the PMBus interface.

Equation 2.

where

• R5 and R_ESR are in Ω
• C4 is in F (suggest 100 nF
• L is in H

The maximum acceptable voltage across the ISNS pins is 110 mV. Because most inductors have a copper conductor and because copper has a fairly large temperature coefficient of resistance, the resistance of the inductor and the current through the inductor should make a DC voltage less than 110 mV when the inductor is at the maximum temperature for the converter. This also applies for the external resistor shown in Figure 19. The full load output current multiplied by the sense resistor value, must be less that 110 mV at the maximum converter operating temperature.

There is also a constraint on the negative (reverse current) voltage that can be applied to the ISNS pins of the TPS40400 device. The voltage differential from the ISNS+ pin to the ISNS– should not be less than –45 mV. If this condition is not met, inaccurate results from the READ_IOUT command occur. This requirement is intended to limit the ripple voltage. The net current through the inductor must flow towards the load from the input voltage. It is possible for the device to accommodate current sinking, but the device does not support current sinking in overcurrent detection or in the READ_IOUT command.

In all cases, place the component C4 as close as possible to the ISNSx pins to help avoid problems with noise.

Figure 18. Current Sensing Using Inductor Resistance

Figure 19. Current Sensing Using Sense Resistor

After the current sensing method is chosen, determine the resistance of the current sense element. This method allows the proper calculation of thresholds for the overcurrent fault and warning, as well as more accurate reporting of the actual output current. The IOUT_CAL_GAIN command is used to set the value of the sense element resistence of the device. The IOUT_OC_WARN_LIMIT and IOUT_OC_FAULT_LIMIT commands set the levels for the overcurrent warning and fault levels respectively. (See the PMBus Functionality and Additional Set-Up section for more details.)

7.3.4 Linear Regulators

Two on-board linear regulators provide power for the internal circuitry of the device. Pin BP3 and BP6 must be bypassed to function properly. The BP3 pin requires a minimum of 100 nF connected between it and GND. The BP6 pin requires approximately 1 µF connected between it and GND.

The external regulator can power other circuits but only if the loads placed on the regulators do not adversely affect operation of the device. Avoid loads with heavy transient currents that can affect the regulator outputs. Transient voltages on these outputs could result in noisy or erratic operation of the TPS40400 device.

It is important to consider current limits. Shorting the BP3 pin to GND damages the BP3 regulator. The BP3 regulator input comes from the BP6 regulator output. The current limit circuit on the BP6 regulator is 100 mA so the total current drawn from both regulators must be less than that. This total current includes the TPS40400 device operating current , _VDD, plus the gate-drive current required to drive the power MOSFETs. The total available current from two regulators is found in Equation 3 and Equation 4:

Equation 3.

Equation 4.

where

• I_LIN is the total current that can be drawn from BP3 and BP6 in aggregate
• I_BP6 is the current limit of the BP6 regulator (minimum 100 mA)
• I_VDD is the quiescent current of the TPS40400 device ( maximum 15 mA)
• I_GATE is the gate drive current required by the power MOSFETs
• f_SW is the switching frequency
• Q_gHIGH is the total gate charge required by the high-side MOSFET
• Q_gLOW is the total gate charge required by the low-side MOSFET

7.3.5 PMBus Address

Each device connected to the PMBus interface must have a unique address on the bus acording to the PMBus specification . The TPS40400 device has 64 possible addresses (0 through 63 in decimal) that can be assigned by connecting resistors from the ADDR0 and ADDR1 pins to SGND. The address is set in the form of two octal (0-7) digits, one digit for each pin. ADDR1 is the high-order digit and ADDR0 is the low-order digit.

The E96 series resistors suggested for each digit value are shown in Table 1.

The TPS40400 device detects values that are out of range on the ADDR0 and ADDR1 pins. If either pin is detected as having an out of range resistance connected to it, the TPS40400 device continues to respond to PMBus commands at address 127, which is outside of the possible programmed addresses. It is possible (but not recommended) to use the device in this condition, especially if other TPS40400 devices are present on the bus or if another device could possibly occupy the 127 address.

7.3.6 PMBus Connections

The TPS40400 supports both the 100-kHz and 400-kHz bus speeds. Connection for the PMBus interface should follow the High Power DC specifications given in section 3.1.3 in the SMBus specification V2.0 for the 400-kHz bus speed or the Low Power DC specifications in section 3.1.2. The complete SMBus specification is available from the SMBus web site, smbus.org.

7.3.7 PMBus Functionality and Additional Set-Up

7.3.7.1 Data Format

Three supported PMBus data format commands require representation of a literal number as their argument (commands that set thresholds, set voltages or report those types of settings). A compatible device needs to support only one of these formats. The TPS40400 device supports the Linear data format only for these commands. In this format, the data argument consists of two parts, a mantissa and an exponent. The number represented by this argument can be expressed as shown in Equation 5.

Equation 5.

7.3.7.2 Output Voltage Adjustment

The VOUT_TRIM command adjusts the nominal output voltage of the device. (See the VOUT_TRIM (22h) command description for the format of this command as used in the TPS40400 device.) The adjustment range is ±25% from the nominal output voltage. The VOUT_TRIM command is used to trim the final output voltage of the device without relying on high-precision resistors being used as described in the Figure 17 section. The resolution of the adjustment is 7 bits, with a resulting minimum step size of approximately 0.4%. The output margining function uses this same 7 bit structure so the total combined deviation from the nominal output for margining and VOUT_TRIM is still limited to ±25%. Exceeding this range causes errors.

In order for the PMBus output voltage adjustments to function correctly, the VOUT_SCALE_LOOP parameter must be set properly. VOUT_SCALE_LOOP is a PMBus command (see Supported PMBus Commands) that reports the ratio of the voltage divider that sets the nominal output voltage is. The data for this command is the ratio of the divider that is used to set the output voltage. From Figure 17, VOUT_SCALE_LOOP parameter can be calculated using Equation 6.

Equation 6.

The resolution of the VOUT_SCALE_LOOP command is 0.00195, or slightly less than 0.2% due to the data format of the command (the linear data mode exponent is fixed at –9 for this command). This granularity affects the accuracy of adjustments to the output voltage made using the PMBus (VOUT_TRIM, VOUT_MARGIN_HIGH and VOUT_MARGIN_LOW) as well as setting the overvoltage and undervoltage fault and warning levels. These commands use the VOUT_SCALE_LOOP parameter to calculate the following requirements

• required reference voltage for the requested output voltage
• required thresholds referenced to the FB pin for the requested warning and fault levels

When the VOUT_SCALE_LOOP parameter has been properly set, the commands that adjust the output voltage function properly. The TPS40400 can be in one of three states when considering what the actual output voltage is:

• No output margin
• Margin high
• Margin low

The OPERATION command setting determines the output state. The FB pin reference voltage is calculated as follows in each of these states.

No margin voltage:

Equation 7.

Margin high voltage state:

Equation 8.

Margin low state:

Equation 9.

where

• V_FB is the FB pin voltage
• VOUT_TRIM is the offset voltage in volts to be applied to the output voltage
• VOUT_SCALE_LOOP is the output voltage divider scale parameter
• VOUT_MARGIN_HIGH is the requested margin high voltage
• VOUT_MARGIN_LOW is the requested margin low voltage

For these conditions, the output voltage is shown in Equation 10.

Equation 10.

where

• V_FB is the pin voltage calculated in Equation 7
• R2 and R1 are in consistent units from Figure 17
• VOUT is the output voltage

NOTE

The sum of the margin and trim voltages cannot be more that ±25% from the nominal output voltage. The FB pin voltage can deviate no more that this from the nominal 600 mV.

When using the margin commands, the soft-start time (t_SS, set by TON_RISE and the output voltage information available to the device using the VOUT_SCALE_LOOP command) determines the transition rate between any two of the three states (margin high, no margin and margin low) . The transition rate between margin states is the same volts-per-second as the soft-start time, assuming that the user has input the correct value for VOUT_SCALE_LOOP.

7.3.7.3 Overcurrent Threshold

The PMBus interface provides adjustable overcurrent in the TPS40400 device. To function properly, the device requires a value for the current sensing element resistance. Issuing the IOUT_CAL_GAIN command with the argument set to the resistance of the sense element establishes this setting. (See the IOUT_CAL_GAIN (38h) command description). The resolution of this command is 30.5 µΩ and the range is 0 to 15.6 mΩ.

Another command, IOUT_CAL_OFFSET (see the IOUT_CAL_OFFSET (39h) command description section) can be used to trim out offset errors in the READ_IOUT command results, overcurrent warning and fault level thresholds. The resolution of this command is 62.5 mA Offsets cannot be trimmed closer than half of this amount. The range for this command is -4 A to 3.937 A. Calibrating offsets to a level greater than this is not possible.

After IOUT_CAL_GAIN and IOUT_CAL_OFFSET parameters have been set, the IOUT_OC_WARN_LIMIT and IOUT_OC_FAULT_LIMIT limit commands can be used to set the overcurrent warning and fault thresholds for the device. There are two resolution limiting factors in setting the overcurrent thresholds.

• IOUT_OC_WARN_LIMIT and IOUT_OC_FAULT_LIMIT commands
• Overcurrent DAC can result in lower resolution.

The resolution available in the IOUT_OC_WARN_LIMIT and IOUT_OC_FAULT_LIMIT commands is 500 mA. This limit is the absolute minimum adjustment that can be made to these thresholds.

The overcurrent detection is accomplished using a DAC to set the threshold and a comparator to sense when the actual current level is above that threshold. The resolution of the DAC is 1.875 mV. The resistance of the current sense element and this resolution determine the minimum adjustment that can be made to the overcurrent warning and fault thresholds. That minimum adjustment is given in Equation 11.

Equation 11.

where

• I_ΔOC is the minimum change that can be made in the overcurrent warning or fault threshold
• R_ISNS is the resistance of the current sensing element, either the inductor DC resistance or the resistance of the current sense resistor used

Combining these two resolution limits shows that for current sense elements with a resistance below 3.75 mΩ, the overcurrent resolution is given by Equation 11. For current sense element resistances above 3.75 mΩ, the overcurrent warning and fault resolution is 500 mA.

The TPS40400 device has built in temperature correction for the temperature coefficient of resistance for copper wound inductors used as current sense elements. As the temperature of a copper wound inductor increases, its resistance increases, resulting in a higher DC component of voltage across it for a given current. This leads to a decrease in the current that would actually trip the overcurrent thresholds. The voltages that the device uses to represent the overcurrent thresholds is automatically adjusted higher as the die temperature of the device increases. The temperature coefficient for the increase of the thresholds is chosen close to the temperature coefficient of copper at 4000 ppm/°C. The change in overcurrent threshold voltage from one temperature to another is given in Equation 12.

Equation 12.

where

• V_OC1 and V_OC2 are the overcurrent threshold voltages
• T1 and T2 are the corresponding temperatures in °C
• T_CCU is the temperature coefficient, 0.004

The change in overcurrent threshold voltages given in Equation 12 maintains the actual overcurrent trip points to a near-constant level only if the die temperature of the device and the copper temperature of the inductor are closely coupled. If the inductor copper temperature rises higher than the die temperature, the overcurrent thresholds appears to decrease and vice versa.

Temperature compensation applied to the overcurrent thresholds must be considered. The threshold voltage must not be or become greater (with the internal temperature compensation) than 110 mV referred to the voltage at the ISNS pins. For instance, when a 10-mΩ resistance inductor is used as the current sense element, a current of 10 A causes a 100-mV DC level at the current sense pins. Initially, this is measurement is within the bounds of the 110 mV limit of the device. However, the temperature compensation of the threshold inside the device raises the effective threshold as the TPS40400 die temperature increases. For a 100°C increase in die temperature, for example, the effective threshold crossed at the ISNS pins to trip an overcurrent is approximately 140 mV at the ISNS pins. The device cannot respond to this level and the result is a failure of the overcurrent mechanism to respond at higher die temperatures. For a given maximum temperature defined by the characteristics of the particular application, Equation 13 shows the maximum overcurrent setting that should be made for the device.

Equation 13.

where

• I_MAX is the maximum overcurrent threshold setting permissible (using the IOUT_OC_FAULT_LIMIT command) in A
• V_ISNS(max) is the maximum allowable voltage differential at the ISNS pins, 120 mV R_ISNS is the resistance of the current sensing element – either inductor or current sense resistor
• T_MAX is the maximum junction temperature expected for the TPS40400 device in °C
• TC_CU is the temperature coefficient of resistance for copper, 0.004

Figure 20 shows the variation described in Equation 13; the internal overcurrent threshold as the die temperature increases. In this example, the designated maximum die temperature is 125°C. For the overcurrent threshold to be valid at this temperature (110 mV or below), the maximum overcurrent threshold required using the IOUT_OC_FAULT or IOUT_OC_WARN commands should correspond to no more than 75.7 mV. Equation 13 calculates the current level that achieves this threshold. If the maximum expected die temperature is less than 125°C, then the maximum 25°C overcurrent threshold increases accordingly.

Figure 20. Internal Overcurrent Threshold Variation

7.3.7.5 Soft-Start Time

The TPS40400 device supports several soft-start times from 600 μs to 9 ms selected by the TON_RISE PMBus command. See the TON_RISE (61h) command description section for full details on the levels and implementation. When selecting the soft-start time, consider the charging current for the output capacitors. In some applications (for example, those with large amounts of output capacitance) this current can lead to problems with nuisance tripping of the overcurrent protection circuitry. To avoid nuisance tripping, include the output capacitor charging current when considering where to set the overcurrent threshold. Equation 14 calculates the output capacitor charging current.

Equation 14.

where

• I_CAP is the start-up charging current of the output capacitance in A
• V_OUT is the output voltage of the converter in V
• C_OUT is the total output capacitance in F
• t_SS is the selected soft-start time in seconds

After calculating the charging current, calibrate the overcurrent threshold to the sum of the maximum load current and the output capacitor charging current plus some margin. The amount of margin required depends on the individual application, but 25% is a suggested starting point. More or less margin may be required.

7.4.1 Continuous Conduction Mode

The TPS40400 device operates in continuous conduction mode (CCM) at a fixed frequency, regardless of the output current.

7.4.2 Operation with CNTL Signal Control

According to the value in the ON_OFF_CONFIG register, the TPS40400 device can be commanded to use the CNTL pin to enable or disable regulation, regardless of the state of the OPERATION command. The minimum input high threshold for the CNTL signal is 2.1 V. The maximum input low threshold for the CNTL signal is 0.8 V. The CNTL pin can be configured as either active high or active low (inverted) logic.

7.4.3 Operation with OPERATION Control

According to the value in the ON_OFF_CONFIG register, TPS40400 device can be commanded to use the OPERATION command to enable or disable regulation, regardless of the state of the CNTL signal.

7.4.4 Operation with CNTL and OPERATION Control

According to the value in the ON_OFF_CONFIG register determines how regulation is enabled or disabled, this device can be commanded to require both a signal on the CNTL pin, and the OPERATION command to enable or disable regulation.

7.4.5 Operation without CNTL or OPERATION Control

According to the value in the ON_OFF_CONFIG register, this device can be commanded to convert power whenever the sensed input voltage is above the programmed UVLO thresholds, VIN_ON and VIN_OFF.

7.4.6 Operation with Output Trim and Margin

The OPERATION command toggles the device between three states:

• Margin None
• Margin Low
• Margin High

In the margin none state, the feedback reference, VREF, is equal to the nominal 600-mV reference, plus any offset defined by the VOUT_TRIM command. In the margin low state, a negative offset defined by the VOUT_MARGIN_LOW command is applied to the feedback reference, moving the converter output voltage down by an equivalent percentage. In the margin high state, a positive offset defined by the VOUT_MARGIN_HIGH command is applied to the feedback reference, moving the converter output voltage up by an equivalent percentage.

7.5.1 Supported PMBus Commands

7.6.1 OPERATION (01h)

The OPERATION command is used to turn the device output on or off in conjunction with the input from the CONTROL pin. It is also used to set the output voltage to the upper or lower MARGIN voltages. The unit stays in the commanded operating mode until a subsequent OPERATION command or a change in the state of the CONTROL pin instructs the device to change operation modes.

From Margin Low (Act on Fault), output overvoltage (OV) events report in the STATUS registers, but regulation continues, regardless of the VOUT_OV_FAULT_RESPONSE command settings. Output undervoltage faults continue to cause the converter to respond according to the VOUT_UV_FAULT_RESPONSE command settings.

Likewise, from Margin High (Act on Fault), output undervoltage (UV) events report in the STATUS registers, but regulation continues regardless of the VOUT_UV_FAULT_RESPONSE command settings. Output overvoltage faults continue to cause the converter to respond according to the settings in the VOUT_OV_FAULT_RESPONSE command.

7.6.2 ON_OFF_CONFIG (02h)

The ON_OFF_CONFIG command configures the combination of CNTL pin input and serial bus commands needed to turn the unit on and off. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

7.6.3 CLEAR_FAULTS (03h)

The CLEAR_FAULTS command is used to clear any fault bits that have been set. This command clears all bits in all status registers simultaneously. At the same time, the device negates (clears, releases) its SMBALERT signal output if the device is asserting the SMBALERT signal. The CLEAR_FAULTS command does not cause a unit that has latched off for a fault condition to restart. If the fault is still present when the bit is cleared, the fault bit is immediately reset and the host notified by the usual means.

7.6.4 WRITE_PROTECT (10h)

The WRITE_PROTECT command is used to control writing to the PMBus device. The intent of this command is to provide protection against accidental changes. This command is not intended to provide protection against deliberate or malicious changes to the device configuration or operation. All supported command parameters may have their parameters read, regardless of the WRITE_PROTECT settings. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

In any case, only one of the three bits may be set at any one time. Attempting to set more than one bit results in an alert being generated and the cml bit is STATUS_WORD being set.

7.6.5 STORE_DEFAULT_ALL (11h)

The STORE_DEFAULT_ALL command stores all of the current storable register settings in the EEPROM memory as the new defaults on power up.

It is permissible to use this command while the device is switching. Note however that the device continues to switch but ignores all fault conditions until the internal store process has completed.

EEPROM programming faults cause the device to NACK and set the 'cml' bit in the STATUS_BYTE and the 'oth' bit in the STATUS_CML registers.

7.6.6 RESTORE_DEFAULT_ALL (12h)

The RESTORE_DEFAULT_ALL command restores all of the storable register settings from EEPROM memory.

Do not use this command while the device is actively switching. If this command is used during active switching, the device stops switching the output drivers and the output voltage drops. Depending on loading conditions, the output voltage could reach an undervoltage level and trigger an undervoltage fault response if programmed to do so. The TPS40400 device will not prevent the user from issuing this command during regulation, but it is not recommended as it results in a restart that could disrupt power sequencing requirements in more complex systems. It is strongly recommended that the device be stopped before issuing this command.

7.6.7 STORE_DEFAULT_CODE (13h)

The STORE_DEFAULT_CODE command instructs the PMBus core to store the contents of the programming register whose Command Code matches the value in the data byte into memory as the new default value.

EEPROM programming faults cause the device to NACK and set the ‘cml’ bit in the STATUS_BYTE and the ‘oth’ bit in the STATUS_CML registers. It is permissible to use this command while the device is switching. Note however that the device continues to switch but ignores all fault conditions until the internal store process has completed.

It is permitted to use the STORE_DEFAULT_CODE command while the device is operating. However, the device may be unresponsive during the copy operation with unpredictable, undesirable or even catastrophic results. It is recommended to turn off the device output before issuing this command.

7.6.8 RESTORE_DEFAULT_CODE (14h)

The RESTORE_DEFAULT_CODE command instructs the PMBus core to overwrite the programming register whose Command Code matches the value in the data byte, with the default value.

The RESTORE_DEFAULT_CODE command should not be used while the device is switching because the device stops switching and restarts. During the restart, the low-side driver turns on for an extended time period and could damage loads that are sensitive to the power rail sinking current. If this is of no concern then the command may be used while the device is switching.

7.6.9 VOUT_MODE (20h)

The PMBus specification dictates that the data word for the VOUT_MODE command is one byte that consists of a 3-bit mode and 5-bit exponent parameter, as shown below. The 3-bit mode sets whether the device uses the Linear or Direct modes for output voltage related commands. The 5-bit parameter sets the exponent value for the linear data mode. The mode and exponent parameters are set and do not permit the user to change the values.

7.6.10 VOUT_TRIM (22h)

The VOUT_TRIM command is used to apply a fixed offset voltage to the output voltage command value. It is most typically use by the end user to trim the output voltage at the time the PMBus device is assembled into the end user system. It is vital that the VOUT_SCALE_LOOP comand is set correctly in order to obtaining correct results. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

The effect of this command is determined by the settings of the VOUT_MODE command. In this device, the VOUT_MODE is fixed to Linear with an exponent of –10 (decimal).

Equation 15.

The maximum value of V_OUT(offst) is ±25% of nominal VOUT. Nominal V_OUT is set by external resistors and the 600 mV error amplifier reference. The valid range in 2s complement for this command is –4000h to 3FFF. The high order two bits of the high byte must both be either 0 or 1. They cannot have different values. If a value outside of the ±25% is given with this command, the TPS40400 device sets the output voltage to the upper or lower limit depending on the direction of the setting, assert SMBALRT, set the CML bit in STATUS_BYTE and the invalid data bit STATUS_CML.

7.6.11 VOUT_MARGIN_HIGH (25h)

The VOUT_MARGIN_HIGH command sets the target voltage which the output changes to when the OPERATION command is set to "Margin High". The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

The effect of this command is determined by the settings of the VOUT_MODE command. In this device, the VOUT_MODE is fixed to Linear with an exponent of –10 (decimal). The actual output voltage commanded by a margin high command can be found by:

Equation 16.

The maximum margin range is ±25% of nominal VOUT. Nominal VOUT is set by external resistors and a 600 mV error amplifier reference and does not include the offset generated by VOUT_TRIM. It is critical that the correct value be programmed into VOUT_SCALE_LOOP for the correct margin value to be calculated. Error checking is not performed when the VOUT_MARGIN_HIGH command is issued. The error checking is done when the OPERATION command is issued calling for a margin high state. At that time, values outside the ±25% range is treated as invalid data and causes the set the CML bit in the STATUS_BYTE and the invalid data (ivd) bit in the STATUS_CML registers. The output voltage is then set to to the upper or lower limit depending on the direction of the setting. The device state can be restored to power up defaults by issuing either the RESTORE_DEFAULT_ALL or RESTORE_DEFAULT_CODE commands.

The default value of VOUT_MARGIN_HIGH is 0x547 or 1351. This corresponds to a default margin high voltage of 1.32 V with the default VOUT_SCALE_LOOP value of 0.5 and external resistor selection to give 1.2 V nominal output voltage.

7.6.12 VOUT_MARGIN_LOW (26h)

The VOUT_MARGIN_LOW command sets the target voltage which the output changes to when the OPERATION command is set to "Margin Low". The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

The effect of this command is determined by the settings of the VOUT_MODE command. In this device, the VOUT_MODE is fixed to Linear with an exponent of –10 (decimal). The actual output voltage commanded by a margin high command can be found by:

Equation 17.

The maximum margin range is ±25% of nominal VOUT. Nominal VOUT is set by external resistors and a 600 mV error amplifier reference and does not include the offset generated by VOUT_TRIM. It is critical that the correct value be programmed into VOUT_SCALE_LOOP for the correct margin value to be calculated. Error checking is not performed when the VOUT_MARGIN_LOW command is issued. The error checking is done when the OPERATION command is issued calling for a margin high state. At that time, values outside the ±25% range is treated as invalid data and causes the device to set the CML bit in the STATUS_BYTE and the invalid data (ivd) bit in the STATUS_CML registers. The output voltage is then set to the upper or lower limit depending on the direction of the setting. The device state can be restored to power up defaults by issuing either the RESTORE_DEFAULT_ALL or RESTORE_DEFAULT_CODE commands.

The default value of VOUT_MARGIN_LOW is 0x451 or 1105. This corresponds to a default margin high voltage of 1.08 V with the default VOUT_SCALE_LOOP value of 0.5 and external resistor selection to give 1.2 V nominal output voltage.

7.6.13 VOUT_SCALE_LOOP (29h)

VOUT_SCALE_LOOP is equal to the feedback resistor ratio. The nominal output voltage is set by a resistor divider and the internal 600mV reference voltage. The default value of VOUT_SCALE_LOOP is 0.5 meaning that the reference voltage is one half of the output voltage. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

The correct setting for the VOUT_SCALE_LOOP parameter is shown in Equation 18.

Equation 18.

It is important that this parameter is set correctly because it has an effect on several other parameters. Any parameter that operates on or reports output voltage depends on the correct setting of this parameter for correct results to be obtained.

7.6.14 FREQUENCY_SWITCH (33h)

The FREQUENCY_SWITCH command sets the switching frequency. TPS40400 device only supports frequencies from 200 kHz to 2 MHz. Values written within the supported frequency range is rounded up to the nearest supported increment. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

There are 14 distinct supported frequencies:

• 200 kHz
• 300 kHz
• 400 kHz
• 500 kHz
• 600 kHz (default)
• 700 kHz
• 800 kHz
• 900 kHz
• 1.0 MHz
• 1.2 MHz
• 1.4 MHz
• 1.6 MHz
• 1.8 MHz
• 1.9 MHz

The data word that accompanies this command is divided into a fixed 5-bit exponent and an 11-bit mantissa. The 5 most significant bits of the mantissa are fixed, while the lower six bits may be altered.

7.6.15 VIN_ON (35h)

The VIN_ON command sets the value of the input voltage at which the unit should start operation assuming all other required start-up conditions are met. Values are mapped to the nearest supported increment. Values outside the supported range are treated as invalid data and cause the device set the CML bit in the STATUS_BYTE and the invalid data (ivd) bit in the STATUS_CML registers. The value of VIN_ON remains unchanged on an out-of-range write attempt. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

VIN_ON must be set higher than VIN_OFF. Attempting to write either VIN_ON lower than VIN_OFF or VIN_OFF higher than VIN_ON results in the new value being rejected, SMBALERT being asserted along with the CML bit in STATUS_BYTE and the invalid data bit in STATUS_CML.

The data word that accompanies this command is divided into a fixed 5-bit exponent and an 11-bit mantissa. The four most significant bits of the mantissa are fixed, while the lower 7 bits may be altered.

7.6.16 VIN_OFF (36h)

The VIN_OFF command sets the value of the input voltage at which the unit should stop operation. Values are mapped to the nearest supported increment. Values outside the supported range is treated as invalid data and causes the device to set the CML bit in the STATUS_BYTE and the invalid data (ivd) bit in the STATUS_CML registers. The value of VIN_ON remains unchanged during an out-of-range write attempt. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

VIN_ON must be set higher than VIN_OFF. Attempting to write either VIN_ON lower than VIN_OFF or VIN_OFF higher than VIN_ON resultx in the new value being rejected, SMBALERT being asserted along with the CML bit in STATUS_BYTE and the invalid data bit in STATUS_CML.

The data word that accompanies this command is divided into a fixed 5 bit exponent and an 11 bit mantissa. The 4 most significant bits of the mantissa are fixed, while the lower 7 bits may be altered.

7.6.17 IOUT_CAL_GAIN (38h)

The IOUT_CAL_GAIN is the ratio of the voltage at the current sense element to the sensed current. The units are Ohms (Ω). The effective current sense element can be the DC resistance of the inductor or a separate current sense resistor. The default setting is 3 mΩ, and the resolution is 30.5 µΩ. The range is 0 to 15.6 mΩ. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

7.6.18 IOUT_CAL_OFFSET (39h)

The IOUT_CAL_OFFSET is used to compensate for offset errors in the READ_IOUT results and the IOUT_OC_FAULT_LIMIT and IOUT_OC_WARN_LIMIT thresholds. The units are amps. The default setting is 0 amps. The resolution of the argument for this command is 62.5 mA and the range is +3937.5mA to -4000 mA. Values written outside of this range alias into the supported range. For example, 1110 0100 0000 0001 has an expected value of –63.0625 amps, but results in 1110 0111 1111 0001 which is –0.9375 A. This occurs because the read-only bits are fixed. The Exponent is always –4 and the 5 msb bits of the Mantissa are always equal to the sign bit. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

7.6.19 VOUT_OV_FAULT_LIMIT (40h)

The VOUT_OV_FAULT_LIMIT command sets the value of the output voltage that causes an output overvoltage fault. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

The effective value of this command is determined by the settings of the VOUT_MODE command. In this device, the VOUT_MODE is fixed to Linear with an exponent of –10 (decimal) so the effective overvoltage trip point requested is:

Equation 19.

The VOUT_OV_FAULT_LIMIT has two data bytes formatted as 2's complement binary integer. The actual values for the VOUT_ OV_FAULT_LIMIT trip point are set to fixed percentages of nominal V_OUT. There are four fixed percentages of the nominal V_OUT that are supported for overvoltage trip points.

• 108%
• 110%
• 112% (default)
• 115%

For example, for a 1.2V nominal output, VOUT_OV_FAULT_LIMIT can be set to 1.296 V, 1.32 V, 1.344 V or 1.38 V. Values within the supported range is set to the nearest fixed percentage. It is critical that the correct value be programmed into VOUT_SCALE_LOOP for the correct overvoltage fault trip point to be calculated. Values outside the supported range results in the corresponding extreme value to be selected. No error conditions are reported

7.6.20 VOUT_OV_FAULT_RESPONSE (41h)

Description: The VOUT_OV_FAULT_RESPONSE command instructs the device on what action to take in response to a VOUT_OV_FAULT_LIMIT fault. The device also:

• Sets the VOUT_OV bit in the STATUS_BYTE
• Sets the VOUT bit in the STATUS_WORD
• Sets the VOUT_OV fault bit in the STATUS_VOUT register, and
• Notifies the host via SMBALRT pin

The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

A one-byte unsigned binary data argument is used with this command:

7.6.21 VOUT_UV_FAULT_LIMIT (44h)

The VOUT_UV_FAULT_LIMIT command sets the value of the output voltage that causes an output undervoltage fault. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

The effective value of this command is determined by the settings of the VOUT_MODE command. In this device, the VOUT_MODE is fixed to Linear with an exponent of –10 (decimal) so the effective overvoltage trip point requested is:

Equation 20.

The VOUT_UV_FAULT_LIMIT has two data bytes formatted as two's complement binary integer. The actual values for VOUT_ UV_FAULT_LIMIT trip point are set to fixed percentages of nominal VOUT. There are four fixed percentages of V_OUT that are supported for overvoltage trip points.

• 92%
• 90%
• 88% (default)
• 85%

For example, for a 1.2 V nominal output, VOUT_UV_FAULT_LIMIT can be set to 1.104 V, 1.08 V, 1.056 V or 1.02 V. Values within the supported range are set to the nearest fixed percentage. It is critical that the correct value be programmed into VOUT_SCALE_LOOP for the correct overvoltage fault trip point to be calculated. Values outside the supported range results in the corresponding extreme value to be selected. No error conditions are reported.

The VOUT_UV_FAULT_LIMIT command has two bytes formatted as a two’s compliment binary integer:

7.6.22 VOUT_UV_FAULT_RESPONSE (45h)

The VOUT_UV_FAULT_RESPONSE command instructs the device on what action to take in response to a VOUT_UV_FAULT_LIMIT fault. The device also:

• Sets the VOUT bit in the STATUS_WORD
• Sets the VOUT UV Fault bit in the STATUS_VOUT register, and
• Notifies the host via SMBALRT pin

The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

A one-byte unsigned binary data word is used with this command:

7.6.23 IOUT_OC_FAULT_LIMIT (46h)

The IOUT_OC_FAULT_LIMIT command sets the value of the output current, in amperes, that causes the over-current detector to indicate an over-current fault condition. The IOUT_OC_FAULT_LIMIT should be set to equal to or greater than the IOUT_OC_WARN_LIMIT. Writing a value to IOUT_OC_FAULT_LIMIT less than IOUT_OC_WARN_LIMIT causea the device to set the CML bit in the STATUS_BYTE and the invalid data (ivd) bit in the STATUS_CML registers as well as assert the SMBALRT signal. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

The IOUT_OC_FAULT_LIMIT takes a two-byte data word formatted as follows:

7.6.23.2 Mantissa

The upper five bits are fixed at 0.
The lower six bits are programmable with a default value of 20 (dec)

The actual output current for a give mantissa and exponent is shown in Equation 21.

Equation 21.

The default output fault current setting is 10 A. Values of I_OUT(oc) can range between 0 A and 35 A in 500-mA increments.

7.6.24 IOUT_OC_FAULT_RESPONSE (47h)

The IOUT_OC_FAULT_RESPONSE command instructs the device on what action to take in response to an IOUT_OC_FAULT_LIMIT fault. The device also:

• Sets the IOUT_OC bit in the STATUS_BYTE
• Sets the IOUT/POUT bit in the STATUS_WORD
• Sets the IOUT OC Fault bit in the STATUS_IOUT register, and
• Notifies the host as described in section 10.2.2 of the PMBus Specification.

The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

7.6.25 IOUT_OC_WARN_LIMIT (4Ah)

The IOUT_OC_WARN_LIMIT command sets the value of the output current, in amperes, that causes the over-current detector to indicate an over-current warning. When this current level is exceeded the device:

• Sets the OTHER bit in the STATUS_BYTE
• Sets the OCW bit in the STATUS_WORD
• Sets the IOUT overcurrent Warning (OCW) bit in the STATUS_IOUT register, and
• Notifies the host by asserting SMBALRT

The IOUT_OC_WARN_LIMIT threshold should always be set to less than or equal to the IOUT_OC_FAULT_LIMIT. Writing a value to IOUT_OC_WARN_LIMIT greater than IOUT_OC_FAULT_LIMIT causes the device to set the CML bit in the STATUS_BYTE and the invalid data (ivd) bit in the STATUS_CML registers as well as assert the SMBALRT signal. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

The IOUT_OC_WARN_LIMIT takes a two byte data word formatted as follows:

7.6.25.2 Mantissa

The upper five bits are fixed at 0.
Lower six bits are programmable with a default value of 15 (dec)

The actual output warning current level for a give mantissa and exponent is:

Equation 22.

The default output fault current setting is 10A. Values of I_OUT(oc) can range from 0 A to 35 A in 500 mA increments. The default output warning current setting is 7.5A.

7.6.26 OT_FAULT_RESPONSE (50h)

The OT_FAULT_RESPONSE command instructs the device on what action to take in response to an output over temperature fault. The temperature sensed is the die temperature of the TPS40400 device only. No other temperature sensors are provided. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands. The OT_FAULT_LIMIT parameter is not programmable and is therefore not supported in the PMBus command set. When an over temperature fault condition is sensed, the device:

• Sets the TEMPERATURE bit in the STATUS_BYTE
• Sets the OT FAULT bit in the STATUS_TEMPERATURE register, and
• Notifies the host by asserting the SMBALRT signal

A one-byte unsigned binary data word is used with this command:

7.6.27 POWER_GOOD_ON (5Eh)

The POWER_GOOD_ON command sets the value of the output voltage at which the PGOOD output pin (open drain) is asserted high. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands. The actual implementation is a window comparator with symmetrical thresholds above and below the nominal. This command sets both the upper and lower power good threshold at the same time. The parameter passed with this command is always the lower threshold (less than the nominal output) and is mapped to the closest supported percentages of the nominal output voltage inTable 36.

For example, with a 1.2 V nominal output voltage, the POWER_GOOD_ON command can set the lower threshold to 1.14 V, 1.104 V or 1.08 V. Doing this automatically sets the upper thresholds to 1.26 V, 1.296 V and 1.32 V respectively.

The effective value of this command is determined by the settings of the VOUT_MODE command. In this device, the VOUT_MODE is fixed to Linear with an exponent of –10 (decimal) so the effective lower power good turn on threshold requested is:

Equation 23.

The nominal output voltage is set by external resistors and a 600-mV error amplifier reference. It is critical that the correct value be programmed into VOUT_SCALE_LOOP in order to correctly select the desired POWER_GOOD_ON threshold.

Normally, the POWER_GOOD_ON threshold is set higher than the POWER_GOOD_OFF threshold. If the POWER_GOOD_ON threshold is set to a value equal to or less than the POWER_GOOD_OFF threshold, the device:

• Sets the CML bit in the STATUS_BYTE
• Sets the Invalid data bit in STATUS_CML
• Notifies the host via SMBALRT pin

It is the user's responsibility to ensure that the chosen POWER_GOOD_ON and POWER_GOOD_OFF thresholds are reasonable with respect to each other. For values written outside the supported ranges are ACK'ed but causes the SMBALRT line to assert and the CML bit to be set in the STATUS_WORD. The invalid data bit is also set in the STATUS_CML results. The actual POWER_GOOD_ON threshold is set to the nearest supported extreme value. For instance, with VOUT_SCALE_LOOP set to 0.5 for a typical 1.2-V output supply, setting POWER_GOOD_ON to 0.5 results in the threshold being set to the 90% value.

The POWER_GOOD_ON command has two data bytes formatted as two’s complement binary integer:

The default value sets the power good turn on threshold to 1.1035V which maps to the 92% low threshold and 108% high threshold.

7.6.28 POWER_GOOD_OFF (5Fh)

The POWER_GOOD_OFF command sets the value of the output voltage at which the PGOOD output pin (open drain output) is de-asserted low. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands. The actual implementation is a window comparator with symmetrical thresholds above and below the nominal. This command sets both the upper and lower power good threshold at the same time. The parameter passed with this command is always the lower threshold (less than the nominal output) and is mapped to the closest supported percentages of the nominal output voltage below:

For example, with a 1.2 V nominal output voltage, the POWER_GOOD_OFF command can set the lower threshold to 1.104 V, 1.0 8V or 1.056 V. Doing this automatically sets the upper thresholds to 1.296 V, 1.32 V and 1.344 V respectively.

The effective value of this command is determined by the settings of the VOUT_MODE command. In this device, the VOUT_MODE is fixed to Linear with an exponent of –10 (decimal) so the effective lower power good turn on threshold requested are:

Equation 24.

The nominal output voltage is set by external resistors and a 600 mV error amplifier reference. It is critical that the correct value be programmed into VOUT_SCALE_LOOP for the correct POWER_GOOD_ON threshold to be selected.

Normally, the POWER_GOOD_ON threshold is set higher than the POWER_GOOD_OFF threshold. If the POWER_GOOD_ON threshold is set to a value equal to or less than the POWER_GOOD_OFF threshold, the device:

• Sets the CML bit in the STATUS_BYTE
• Sets the Invalid data bit in STATUS_CML
• Notifies the host via SMBALRT pin

It is the user's responsibility to make sure that chsen POWER_GOOD_ON and POWER_GOOD_OFF thresholds are reasonable with respect to each other. For values written outside the supported ranges are ACK'ed but cause the SMBALRT line to assert and the CML bit to be set in the STATUS_WORD. The invalid data bit is also set in the STATUS_CML results. The actual POWER_GOOD_OFF threshold is set to the nearest supported extreme value. For instance, with VOUT_SCALE_LOOP set to 0.5 for a typical 1.2-V output supply, setting POWER_GOOD_OFF to 0.5 results in the threshold being set to the 88% value.

The POWER_GOOD_OFF command has two data bytes formatted as two's complement binary integer:

The default value sets the power good turn off threshold to 1.08 V which maps to the 90% low threshold and 108% high threshold.

7.6.29 TON_RISE (61h)

The TON_RISE command sets the time in ms, from when the output starts to rise until the voltage has entered the regulation band. There are several discreet settings that this command supports. Commanding a value other than one of these values results in the nearest supported value being selected.

The supported TON_RISE times over PMBus are as follows. Note that the actual soft-start time is longer than the entered value. Typically the nominal value seen in operation is approximately 15% longer that the time entered.

• 600 µs
• 900 µs
• 1.2 ms
• 1.8 ms
• 2.7 ms (default value)
• 4.2 ms
• 6.0 ms
• 9.0 ms

A value of 0 ms instructs the unit to bring its output voltage to the programmed regulation value as quickly as possible. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

The TON_RISE command is formatted as a linear mode two’s complement binary integer.

7.6.30 STATUS_BYTE (78h)

The STATUS_BYTE command returns one byte of information with a summary of the most critical device faults. For TPS40400 device, 4 fault bits is flagged in this particular command: output over-voltage, output over-current, over-temperature, and output under-voltage. The STATUS_BYTE reports communication faults in the CML bit. Other communication faults set the NONE OF THE ABOVE bit.

A "1" in any of these bit positions indicates that:

7.6.31 STATUS_WORD (78h)

The STATUS_WORD command returns two bytes of information with a summary of the device's fault/warning conditions. The low byte is identical to the STATUS_BYTE above. The additional byte reports the warning conditions for output overvoltage and overcurrent, as well as the power good status of the converter.

A "1" in any of the low byte (STATUS_BYTE) bit positions indicates that:

A "1" in any of the high byte bit positions indicates that:

7.6.32 STATUS_VOUT (7Ah)

The STATUS_VOUT command returns one byte of information relating to the status of the converter's output voltage related faults. The TPS40400 device supports only the VOUT_OV Fault and VOUT_UV Fault bits of this register.

A "1" in any of these bit positions indicates that:

7.6.33 STATUS_IOUT (7Bh)

The STATUS_IOUT command returns one byte of information relating to the status of the converter’s output current related faults. The TPS40400 device supports only the IOUT_OC Fault and IOUT_OC Warning bits of this register.

A "1" in any of these bit positions indicates that:

7.6.34 STATUS_TEMPERATURE (7Dh)

The STATUS_TEMPERATURE command returns one byte of information relating to the status of the converter temperature related faults. The TPS40400 device supports only the OT Fault and OT Warning bits of this register.

A "1" in any of these bit positions indicates that:

7.6.35 STATUS_CML (7Eh)

The STATUS_CML command returns one byte of information relating to the status of the converter’s communication related faults. The bits of this register supported by the TPS40400 device are:

Invalid/Unsuppported Command, Invalid/Unsupported Data, Packet Error Check Failed and Other Communication Fault.

A "1" in any of these bit positions indicates that:

7.6.36 READ_VIN (88h)

The READ_VIN commands returns two bytes of data in the linear data format that represent the input voltage applied to the VDD pin of the device. The data format is as follows:

The input voltage is scaled before it reaches the internal analog to digital converter so that resolution of the input voltage read back is 31.25mV. The input voltage can be found using Equation 25.

Equation 25.

7.6.37 READ_VOUT (8Bh)

The READ_VOUT commands returns two bytes of data in the linear data format that represent the output voltage of the device. The output voltage is sensed at the ISNS- pin so voltage drop to the load is not accounted for. The data format is as follows:

The setting of the VOUT_MODE affects the results of this command as well. VOUT_MODE is set to linear mode with an exponent of –10 and cannot be altered. The output voltage can be found by:

Equation 26.

7.6.38 READ_IOUT (8Ch)

The READ_IOUT commands returns two bytes of data in the linear data format that represent the output current of the device. The output current is sensed at the ISNS+ and ISNS– pins. The data format is as follows:

The output current is scaled before it reaches the internal analog to digital converter so that resolution of the output current read is 62.5 mA, though resolution may be less depending on the setting of IOUT_CAL_GAIN. The maximum value that can be reported is 64 A. It is mandatory that the IOUT_CAL_GAIN and IOUT_CAL_OFFSET parameters are sset correctly in order to obtain accurate results. The output current can be found by using Equation 27.

Equation 27.

7.6.39 PMBUS_REVISION (98h)

The PMBUS_REVISION command returns a single, unsigned binary byte that indicates that the TPS40400 device is compliant with the 1.1 revision of the PMBus specification.

7.6.40 MFR_VIN_MIN (A0h)

The MFR_VIN_MIN command returns a two-byte linear formatted result that indicates the minimum voltage from which the TPS40400 device is able to convert power. The data is formatted as follows:

The minimum input voltage can be found using Equation 28.

Equation 28.

This equates to 3 V when evaluated with the default values. The TPS40400 device begins to convert power at a minimum input of 2.75-V.

7.6.41 MFR_VIN_MAX (A1h)

The MFR_VIN_MAX returns a two-byte linear formatted result that represents the maximum specified operating voltage for the TPS40400 device. The data is formatted as follows:

The maximum input voltage can be found from:

Equation 29.

This equals 20 V when evaluated with the default values.

7.6.42 MFR_VOUT_MIN (A4h)

This command returns a two byte result that represents the minimum output voltage the TPS40400 device supports.

The setting of the VOUT_MODE affects the results of this command. VOUT_MODE is set to linear mode with an exponent of -10 and cannot be altered. The minimum nominal output voltage can be found by:

Equation 30.

This equals to 600 mV using the pre-set values. Using VOUT_TRIM, it is possible to adjust this voltage down to approximately 450 mV.

7.6.43 MFR_VOUT_MAX (A5h)

The command returns a two-byte result that represents the maximum output voltage that the TPS40400 device supports.

The setting of the VOUT_MODE affects the results of this command. VOUT_MODE is set to linear mode with an exponent of –10 and cannot be altered. The maximum nominal output voltage can be found by:

Equation 31.

This evaluates to 12 V using the pre-set values.

7.6.44 MFR_SPECIFIC_00 (D0h)

The MFR_SPECIFIC_00 command is used for storing arbitrary user data and for selecting a dead time or anti-cross conduction time for the TPS40400 device. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

This command take a two byte unsigned binary argument as follows.

7.6.45 MFR_SPECIFIC_01 (D1h)

This command is used for trimming internal components of the TPS40400 device and is not recommended for general use.

7.6.46 MFR_SPECIFIC_02 (D2h)

This command is used for trimming internal components of the TPS40400 device and is not recommended for general use.

7.6.47 MFR_SPECIFIC_03 (D3h)

This command is used for trimming internal components of the TPS40400 device and is not recommended for general use.

7.6.48 MFR_SPECIFIC_04 (D4h)

This command applies an offset to the READ_VOUT command results to calibrate out offset errors in the on board measurement system. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

Default value: 0

Equation 32.

where

• Exponent is fixed at 2^-10 by VOUT_MODE
• LSB value is 975 µV
• Range -125 mV to 124 mV

7.6.49 MFR_SPECIFIC_05 (D5h)

This command applies a gain correction to the READ_VOUT command results to calibrate out gain errors in the on board measurement system. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

Default value: 0

Equation 33.

where

• Exponent is fixed at -8
• LSB value is 0.4%
• Range -0.125 to 0.121

7.6.50 MFR_SPECIFIC_06 (D6h)

This command applies an offset to the READ_VIN command results to calibrate out offset errors in the on board measurement system. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

Default value: 0

Equation 34.

where

• Exponent is fixed at -5
• LSB value is 32 mV
• Range -2 V to 1.968 V

7.6.51 MFR_SPECIFIC_07 (D7h)

This command applies a gain correction to the READ_VIN command results to calibrate out gain errors in the on board measurement system. The contents of this register can be stored to non-volatile memory using the STORE_DEFAULT_ALL or STORE_DEFAULT_CODE commands.

Default value: 0

Equation 35.

where

• Exponent is fixed at -8
• LSB value is 0.4%
• Range -0.125V to 10.121

7.6.52 MFR_SPECIFIC_44 (FCh)

This command returns a two byte unsigned binary 12-bit device identifier code and 4-bit revision code in the following format.

This command is oriented toward providing similar information to the DEVICE_ID command but for devices that do not support block read and write functions.