SBOS448G August 2008 – December 2015 INA219
The INA219 is a digital current sense amplifier with an I2C- and SMBus-compatible interface. It provides digital current, voltage, and power readings necessary for accurate decision-making in precisely-controlled systems. Programmable registers allow flexible configuration for measurement resolution as well as continuous-versus-triggered operation. Detailed register information appears at the end of this data sheet, beginning with Table 2. See the Functional Block Diagram section for a block diagram of the INA219 device.
The two analog inputs to the INA219, IN+ and IN–, connect to a shunt resistor in the bus of interest. The INA219 is typically powered by a separate supply from 3 to 5.5 V. The bus being sensed can vary from 0 to
26 V. There are no special considerations for power-supply sequencing (for example, a bus voltage can be present with the supply voltage off, and vice-versa). The INA219 senses the small drop across the shunt for shunt voltage, and senses the voltage with respect to ground from IN– for the bus voltage. Figure 13 shows this operation.
When the INA219 is in the normal operating mode (that is, MODE bits of the Configuration register are set to 111), it continuously converts the shunt voltage up to the number set in the shunt voltage averaging function (Configuration register, SADC bits). The device then converts the bus voltage up to the number set in the bus voltage averaging (Configuration register, BADC bits). The Mode control in the Configuration register also permits selecting modes to convert only voltage or current, either continuously or in response to an event (triggered).
All current and power calculations are performed in the background and do not contribute to conversion time; conversion times shown in the Electrical Characteristics: can be used to determine the actual conversion time.
Power-Down mode reduces the quiescent current and turns off current into the INA219 inputs, avoiding any supply drain. Full recovery from Power-Down requires 40 μs. ADC Off mode (set by the Configuration register, MODE bits) stops all conversions.
Writing any of the triggered convert modes into the Configuration register (even if the desired mode is already programmed into the register) triggers a single-shot conversion. Table 6 lists the triggered convert mode settings.
Although the INA219 can be read at any time, and the data from the last conversion remain available, the conversion ready bit (Status register, CNVR bit) is provided to help coordinate one-shot or triggered conversions. The conversion ready bit is set after all conversions, averaging, and multiplication operations are complete.
The conversion ready bit clears under any of these conditions:
Current and bus voltage are converted at different points in time, depending on the resolution and averaging mode settings. For instance, when configured for 12-bit and 128 sample averaging, up to 68 ms in time between sampling these two values is possible. Again, these calculations are performed in the background and do not add to the overall conversion time.
If larger full-scale shunt voltages are desired, the INA219 provides a PGA function that increases the full-scale range up to 2, 4, or 8 times (320 mV). Additionally, the bus voltage measurement has two full-scale ranges: 16 or 32 V.
The INA219 is designed for compatibility with hot swap controllers such the TI TPS2490. The TPS2490 uses a high-side shunt with a limit at 50 mV; the INA219 full-scale range of 40 mV enables the use of the same shunt for current sensing below this limit. When sensing is required at (or through) the 50-mV sense point of the TPS2490, the PGA of the INA219 can be set to /2 to provide an 80-mV full-scale range.
Measuring current is often noisy, and such noise can be difficult to define. The INA219 offers several options for filtering by choosing resolution and averaging in the Configuration register. These filtering options can be set independently for either voltage or current measurement.
The internal ADC is based on a delta-sigma (ΔΣ) front-end with a 500-kHz (±30%) typical sampling rate. This architecture has good inherent noise rejection; however, transients that occur at or very close to the sampling rate harmonics can cause problems. Because these signals are at 1 MHz and higher, they can be dealt with by incorporating filtering at the input of the INA219. The high frequency enables the use of low-value series resistors on the filter for negligible effects on measurement accuracy. In general, filtering the INA219 input is only necessary if there are transients at exact harmonics of the 500-kHz (±30%) sampling rate (>1 MHz). Filter using the lowest possible series resistance and ceramic capacitor. Recommended values are 0.1 to 1 μF. Figure 14 shows the INA219 with an additional filter added at the input.
Overload conditions are another consideration for the INA219 inputs. The INA219 inputs are specified to tolerate 26 V across the inputs. A large differential scenario might be a short to ground on the load side of the shunt. This type of event can result in full power-supply voltage across the shunt (as long the power supply or energy storage capacitors support it). It must be remembered that removing a short to ground can result in inductive kickbacks that could exceed the 26-V differential and common-mode rating of the INA219. Inductive kickback voltages are best dealt with by zener-type transient-absorbing devices combined with sufficient energy storage capacitance.
In applications that do not have large energy storage electrolytics on one or both sides of the shunt, an input overstress condition may result from an excessive dV/dt of the voltage applied to the input. A hard physical short is the most likely cause of this event, particularly in applications with no large electrolytics present. This problem occurs because an excessive dV/dt can activate the ESD protection in the INA219 in systems where large currents are available. Testing has demonstrated that the addition of 10-Ω resistors in series with each input of the INA219 sufficiently protects the inputs against dV/dt failure up to the 26-V rating of the INA219. These resistors have no significant effect on accuracy.
An important aspect of the INA219 device is that it measure current or power if it is programmed based on the system. The device measures both the differential voltage applied between the IN+ and IN- input pins and the voltage at IN- pin. In order for the device to report both current and power values, the user must program the resolution of the Current Register (04h) and the value of the shunt resistor (RSHUNT) present in the application to develop the differential voltage applied between the input pins. Both the Current_LSB and shunt resistor value are used in the calculation of the Calibration Register value that the device uses to calculate the corresponding current and power values based on the measured shunt and bus voltages.
After programming the Calibration Register, the Current Register (04h) and Power Register (03h) update accordingly based on the corresponding shunt voltage and bus voltage measurements. Until the Calibration Register is programmed, the Current Register (04h) and Power Register (03h) remain at zero.
The Calibration Register is calculated based on Equation 1. This equation includes the term Current_LSB, which is the programmed value for the LSB for the Current Register (04h). The user uses this value to convert the value in the Current Register (04h) to the actual current in amperes. The highest resolution for the Current Register (04h) can be obtained by using the smallest allowable Current_LSB based on the maximum expected current as shown in Equation 2. While this value yields the highest resolution, it is common to select a value for the Current_LSB to the nearest round number above this value to simplify the conversion of the Current Register (04h) and Power Register (03h) to amperes and watts respectively. The RSHUNT term is the value of the external shunt used to develop the differential voltage across the input pins. The Power Register (03h) is internally set to be 20 times the programmed Current_LSB see Equation 3.
Shunt voltage is calculated by multiplying the Shunt Voltage Register contents with the Shunt Voltage LSB of 10 µV.
The Bus Voltage register bits are not right-aligned. In order to compute the value of the Bus Voltage, Bus Voltage Register contents must be shifted right by three bits. This shift puts the BD0 bit in the LSB position so that the contents can be multiplied by the Bus Voltage LSB of 4-mV to compute the bus voltage measured by the device.
After programming the Calibration Register, the value expected in the Current Register (04h) can be calculated by multiplying the Shunt Voltage register contents by the Calibration Register and then dividing by 4096 as shown in Equation 4. To obtain a value in amperes the Current register value is multiplied by the programmed Current_LSB.
The value expected in the Power register (03h) can be calculated by multiplying the Current register value by the Bus Voltage register value and then dividing by 5000 as shown in Equation 5. Power Register content is multiplied by Power LSB which is 20 times the Current_LSB for a power value in watts.
The Calibration Register enables the user to scale the Current Register (04h) and Power Register (03h) to the most useful value for a given application. For example, set the Calibration Register such that the largest possible number is generated in the Current Register (04h) or Power Register (03h) at the expected full-scale point. This approach yields the highest resolution using the previously calculated minimum Current_LSB in the equation for the Calibration Register. The Calibration Register can also be selected to provide values in the Current Register (04h) and Power Register (03h) that either provide direct decimal equivalents of the values being measured, or yield a round LSB value for each corresponding register. After these choices have been made, the Calibration Register also offers possibilities for end user system-level calibration. After determining the exact current by using an external ammeter, the value of the Calibration Register can then be adjusted based on the measured current result of the INA219 to cancel the total system error as shown in Equation 6.
The INA219 can be used without any programming if it is only necessary to read a shunt voltage drop and bus voltage with the default 12-bit resolution, 320-mV shunt full-scale range (PGA = /8), 32-V bus full-scale range, and continuous conversion of shunt and bus voltage.
Without programming, current is measured by reading the shunt voltage. The Current register and Power register are only available if the Calibration register contains a programmed value.
The default power-up states of the registers are shown in the Register Details section of this data sheet. These registers are volatile, and if programmed to other than default values, must be re-programmed at every device power-up. Detailed information on programming the Calibration register specifically is given in the section, Programming the Calibration Register.
The INA219 offers compatibility with both I2C and SMBus interfaces. The I2C and SMBus protocols are essentially compatible with one another.
The I2C interface is used throughout this data sheet as the primary example, with SMBus protocol specified only when a difference between the two systems is being addressed. Two bidirectional lines, SCL and SDA, connect the INA219 to the bus. Both SCL and SDA are open-drain connections.
The device that initiates the transfer is called a master, and the devices controlled by the master are slaves. The bus must be controlled by a master device that generates the serial clock (SCL), controls the bus access, and generates START and STOP conditions.
To address a specific device, the master initiates a START condition by pulling the data signal line (SDA) from a HIGH to a LOW logic level while SCL is HIGH. All slaves on the bus shift in the slave address byte on the rising edge of SCL, with the last bit indicating whether a read or write operation is intended. During the ninth clock pulse, the slave being addressed responds to the master by generating an Acknowledge and pulling SDA LOW.
Data transfer is then initiated and eight bits of data are sent, followed by an Acknowledge bit. During data transfer, SDA must remain stable while SCL is HIGH. Any change in SDA while SCL is HIGH is interpreted as a START or STOP condition.
Once all data have been transferred, the master generates a STOP condition, indicated by pulling SDA from LOW to HIGH while SCL is HIGH. The INA219 includes a 28-ms timeout on its interface to prevent locking up an SMBus.
To communicate with the INA219, the master must first address slave devices through a slave address byte. The slave address byte consists of seven address bits, and a direction bit indicating the intent of executing a read or write operation.
The INA219 has two address pins, A0 and A1. Table 1 describes the pin logic levels for each of the 16 possible addresses. The state of pins A0 and A1 is sampled on every bus communication and should be set before any activity on the interface occurs. The address pins are read at the start of each communication event.
The INA219 operates only as a slave device on the I2C bus and SMBus. Connections to the bus are made through the open-drain I/O lines SDA and SCL. The SDA and SCL pins feature integrated spike suppression filters and Schmitt triggers to minimize the effects of input spikes and bus noise. The INA219 supports the transmission protocol for fast (1- to 400-kHz) and high-speed (1-kHz to 2.56-MHz) modes. All data bytes are transmitted most significant byte first.
Accessing a particular register on the INA219 is accomplished by writing the appropriate value to the register pointer. Refer to Table 2 for a complete list of registers and corresponding addresses. The value for the register pointer as shown in Figure 18 is the first byte transferred after the slave address byte with the R/W bit LOW. Every write operation to the INA219 requires a value for the register pointer.
Writing to a register begins with the first byte transmitted by the master. This byte is the slave address, with the R/W bit LOW. The INA219 then acknowledges receipt of a valid address. The next byte transmitted by the master is the address of the register to which data will be written. This register address value updates the register pointer to the desired register. The next two bytes are written to the register addressed by the register pointer. The INA219 acknowledges receipt of each data byte. The master may terminate data transfer by generating a START or STOP condition.
When reading from the INA219, the last value stored in the register pointer by a write operation determines which register is read during a read operation. To change the register pointer for a read operation, a new value must be written to the register pointer. This write is accomplished by issuing a slave address byte with the R/W bit LOW, followed by the register pointer byte. No additional data are required. The master then generates a START condition and sends the slave address byte with the R/W bit HIGH to initiate the read command. The next byte is transmitted by the slave and is the most significant byte of the register indicated by the register pointer. This byte is followed by an Acknowledge from the master; then the slave transmits the least significant byte. The master acknowledges receipt of the data byte. The master may terminate data transfer by generating a Not-Acknowledge after receiving any data byte, or generating a START or STOP condition. If repeated reads from the same register are desired, it is not necessary to continually send the register pointer bytes; the INA219 retains the register pointer value until it is changed by the next write operation.
Figure 15 and Figure 16 show write and read operation timing diagrams, respectively. Note that register bytes are sent most-significant byte first, followed by the least significant byte. Figure 17 shows the timing diagram for the SMBus Alert response operation. Figure 18 shows a typical register pointer configuration.
When the bus is idle, both the SDA and SCL lines are pulled high by the pull-up devices. The master generates a start condition followed by a valid serial byte containing high-speed (HS) master code 00001XXX. This transmission is made in fast (400 kbps) or standard (100 kbps) (F/S) mode at no more than 400 kbps. The INA219 does not acknowledge the HS master code, but does recognize it and switches its internal filters to support 2.56 Mbps operation.
The master then generates a repeated start condition (a repeated start condition has the same timing as the start condition). After this repeated start condition, the protocol is the same as F/S mode, except that transmission speeds up to 2.56 Mbps are allowed. Instead of using a stop condition, repeated start conditions should be used to secure the bus in HS-mode. A stop condition ends the HS-mode and switches all the internal filters of the INA219 to support the F/S mode. For bus timing, see Bus Timing Diagram Definitions and Figure 1.
Power-up conditions apply to a software reset through the RST bit (bit 15) in the Configuration register, or the I2C bus General Call Reset.
The INA219 uses a bank of registers for holding configuration settings, measurement results, maximum/minimum limits, and status information. Table 2 summarizes the INA219 registers; Functional Block Diagram shows registers.
Register contents are updated 4 μs after completion of the write command. Therefore, a 4-μs delay is required between completion of a write to a given register and a subsequent read of that register (without changing the pointer) when using SCL frequencies in excess of 1 MHz.
|POINTER ADDRESS||REGISTER NAME||FUNCTION||POWER-ON RESET||TYPE(1)|
|00||Configuration||All-register reset, settings for bus voltage range, PGA Gain, ADC resolution/averaging.||00111001 10011111||399F||R/W|
|01||Shunt voltage||Shunt voltage measurement data.||Shunt voltage||—||R|
|02||Bus voltage||Bus voltage measurement data.||Bus voltage||—||R|
|03||Power(2)||Power measurement data.||00000000 00000000||0000||R|
|04||Current(2)||Contains the value of the current flowing through the shunt resistor.||00000000 00000000||0000||R|
|05||Calibration||Sets full-scale range and LSB of current and power measurements. Overall system calibration.||00000000 00000000||0000||R/W|
All INA219 16-bit registers are actually two 8-bit bytes through the I2C interface.
|LEGEND: R/W = Read/Write; R = Read only; -n = value after reset|
|Bit 15||Setting this bit to '1' generates a system reset that is the same as power-on reset. Resets all registers to default values; this bit self-clears.|
|BRNG:||Bus Voltage Range|
|Bit 13||0 = 16V FSR
1 = 32V FSR (default value)
|PG:||PGA (Shunt Voltage Only)|
|Bits 11, 12||Sets PGA gain and range. Note that the PGA defaults to ÷8 (320mV range). Table 4 shows the gain and range for the various product gain settings.|
|BADC:||BADC Bus ADC Resolution/Averaging|
|Bits 7–10||These bits adjust the Bus ADC resolution (9-, 10-, 11-, or 12-bit) or set the number of samples used when averaging results for the Bus Voltage Register (02h).|
|SADC:||SADC Shunt ADC Resolution/Averaging|
|Bits 3–6||These bits adjust the Shunt ADC resolution (9-, 10-, 11-, or 12-bit) or set the number of samples used when averaging results for the Shunt Voltage Register (01h).
BADC (Bus) and SADC (Shunt) ADC resolution/averaging and conversion time settings are shown in Table 5.
|0||X(2)||0||0||9 bit||84 μs|
|0||X(2)||0||1||10 bit||148 μs|
|0||X(2)||1||0||11 bit||276 μs|
|0||X(2)||1||1||12 bit||532 μs|
|1||0||0||0||12 bit||532 μs|
|Bits 0–2||Selects continuous, triggered, or power-down mode of operation. These bits default to continuous shunt and bus measurement mode. The mode settings are shown in Table 6.|
|0||0||1||Shunt voltage, triggered|
|0||1||0||Bus voltage, triggered|
|0||1||1||Shunt and bus, triggered|
|1||0||0||ADC off (disabled)|
|1||0||1||Shunt voltage, continuous|
|1||1||0||Bus voltage, continuous|
|1||1||1||Shunt and bus, continuous|
The Shunt Voltage register stores the current shunt voltage reading, VSHUNT. Shunt Voltage register bits are shifted according to the PGA setting selected in the Configuration register (00h). When multiple sign bits are present, they will all be the same value. Negative numbers are represented in 2's complement format. Generate the 2's complement of a negative number by complementing the absolute value binary number and adding 1. Extend the sign, denoting a negative number by setting the MSB = 1. Extend the sign to any additional sign bits to form the 16-bit word.
Example: For a value of VSHUNT = –320 mV:
At PGA = /8, full-scale range = ±320 mV (decimal = 32000). For VSHUNT = +320 mV, Value = 7D00h; For VSHUNT = –320 mV, Value = 8300h; and LSB = 10µV.
At PGA = /4, full-scale range = ±160 mV (decimal = 16000). For VSHUNT = +160 mV, Value = 3E80h; For VSHUNT = –160 mV, Value = C180h; and LSB = 10µV.
At PGA = /2, full-scale range = ±80 mV (decimal = 8000). For VSHUNT = +80 mV, Value = 1F40h; For VSHUNT = –80 mV; Value = E0C0h; and LSB = 10µV.
At PGA = /1, full-scale range = ±40 mV (decimal = 4000). For VSHUNT = +40 mV, Value = 0FA0h; For VSHUNT = –40 mV, Value = F060h; and LSB = 10µV.
|Decimal Value||PGA = /8
|PGA = /4
|PGA = /2
|PGA = /1
|320.02||32002||0111 1101 0000 0000||0011 1110 1000 0000||0001 1111 0100 0000||0000 1111 1010 0000|
|320.01||32001||0111 1101 0000 0000||0011 1110 1000 0000||0001 1111 0100 0000||0000 1111 1010 0000|
|320.00||32000||0111 1101 0000 0000||0011 1110 1000 0000||0001 1111 0100 0000||0000 1111 1010 0000|
|319.99||31999||0111 1100 1111 1111||0011 1110 1000 0000||0001 1111 0100 0000||0000 1111 1010 0000|
|319.98||31998||0111 1100 1111 1110||0011 1110 1000 0000||0001 1111 0100 0000||0000 1111 1010 0000|
|160.02||16002||0011 1110 1000 0010||0011 1110 1000 0000||0001 1111 0100 0000||0000 1111 1010 0000|
|160.01||16001||0011 1110 1000 0001||0011 1110 1000 0000||0001 1111 0100 0000||0000 1111 1010 0000|
|160.00||16000||0011 1110 1000 0000||0011 1110 1000 0000||0001 1111 0100 0000||0000 1111 1010 0000|
|159.99||15999||0011 1110 0111 1111||0011 1110 0111 1111||0001 1111 0100 0000||0000 1111 1010 0000|
|159.98||15998||0011 1110 0111 1110||0011 1110 0111 1110||0001 1111 0100 0000||0000 1111 1010 0000|
|80.02||8002||0001 1111 0100 0010||0001 1111 0100 0010||0001 1111 0100 0000||0000 1111 1010 0000|
|80.01||8001||0001 1111 0100 0001||0001 1111 0100 0001||0001 1111 0100 0000||0000 1111 1010 0000|
|80.00||8000||0001 1111 0100 0000||0001 1111 0100 0000||0001 1111 0100 0000||0000 1111 1010 0000|
|79.99||7999||0001 1111 0011 1111||0001 1111 0011 1111||0001 1111 0011 1111||0000 1111 1010 0000|
|79.98||7998||0001 1111 0011 1110||0001 1111 0011 1110||0001 1111 0011 1110||0000 1111 1010 0000|
|40.02||4002||0000 1111 1010 0010||0000 1111 1010 0010||0000 1111 1010 0010||0000 1111 1010 0000|
|40.01||4001||0000 1111 1010 0001||0000 1111 1010 0001||0000 1111 1010 0001||0000 1111 1010 0000|
|40.00||4000||0000 1111 1010 0000||0000 1111 1010 0000||0000 1111 1010 0000||0000 1111 1010 0000|
|39.99||3999||0000 1111 1001 1111||0000 1111 1001 1111||0000 1111 1001 1111||0000 1111 1001 1111|
|39.98||3998||0000 1111 1001 1110||0000 1111 1001 1110||0000 1111 1001 1110||0000 1111 1001 1110|
|0.02||2||0000 0000 0000 0010||0000 0000 0000 0010||0000 0000 0000 0010||0000 0000 0000 0010|
|0.01||1||0000 0000 0000 0001||0000 0000 0000 0001||0000 0000 0000 0001||0000 0000 0000 0001|
|0||0||0000 0000 0000 0000||0000 0000 0000 0000||0000 0000 0000 0000||0000 0000 0000 0000|
|–0.01||–1||1111 1111 1111 1111||1111 1111 1111 1111||1111 1111 1111 1111||1111 1111 1111 1111|
|–0.02||–2||1111 1111 1111 1110||1111 1111 1111 1110||1111 1111 1111 1110||1111 1111 1111 1110|
|–39.98||–3998||1111 0000 0110 0010||1111 0000 0110 0010||1111 0000 0110 0010||1111 0000 0110 0010|
|–39.99||–3999||1111 0000 0110 0001||1111 0000 0110 0001||1111 0000 0110 0001||1111 0000 0110 0001|
|–40.00||–4000||1111 0000 0110 0000||1111 0000 0110 0000||1111 0000 0110 0000||1111 0000 0110 0000|
|–40.01||–4001||1111 0000 0101 1111||1111 0000 0101 1111||1111 0000 0101 1111||1111 0000 0110 0000|
|–40.02||–4002||1111 0000 0101 1110||1111 0000 0101 1110||1111 0000 0101 1110||1111 0000 0110 0000|
|–79.98||–7998||1110 0000 1100 0010||1110 0000 1100 0010||1110 0000 1100 0010||1111 0000 0110 0000|
|–79.99||–7999||1110 0000 1100 0001||1110 0000 1100 0001||1110 0000 1100 0001||1111 0000 0110 0000|
|–80.00||–8000||1110 0000 1100 0000||1110 0000 1100 0000||1110 0000 1100 0000||1111 0000 0110 0000|
|–80.01||–8001||1110 0000 1011 1111||1110 0000 1011 1111||1110 0000 1100 0000||1111 0000 0110 0000|
|–80.02||–8002||1110 0000 1011 1110||1110 0000 1011 1110||1110 0000 1100 0000||1111 0000 0110 0000|
|–159.98||–15998||1100 0001 1000 0010||1100 0001 1000 0010||1110 0000 1100 0000||1111 0000 0110 0000|
|–159.99||–15999||1100 0001 1000 0001||1100 0001 1000 0001||1110 0000 1100 0000||1111 0000 0110 0000|
|–160.00||–16000||1100 0001 1000 0000||1100 0001 1000 0000||1110 0000 1100 0000||1111 0000 0110 0000|
|–160.01||–16001||1100 0001 0111 1111||1100 0001 1000 0000||1110 0000 1100 0000||1111 0000 0110 0000|
|–160.02||–16002||1100 0001 0111 1110||1100 0001 1000 0000||1110 0000 1100 0000||1111 0000 0110 0000|
|–319.98||–31998||1000 0011 0000 0010||1100 0001 1000 0000||1110 0000 1100 0000||1111 0000 0110 0000|
|–319.99||–31999||1000 0011 0000 0001||1100 0001 1000 0000||1110 0000 1100 0000||1111 0000 0110 0000|
|–320.00||–32000||1000 0011 0000 0000||1100 0001 1000 0000||1110 0000 1100 0000||1111 0000 0110 0000|
|–320.01||–32001||1000 0011 0000 0000||1100 0001 1000 0000||1110 0000 1100 0000||1111 0000 0110 0000|
|–320.02||–32002||1000 0011 0000 0000||1100 0001 1000 0000||1110 0000 1100 0000||1111 0000 0110 0000|
The Bus Voltage register stores the most recent bus voltage reading, VBUS.
At full-scale range = 32 V (decimal = 8000, hex = 1F40), and LSB = 4 mV.
At full-scale range = 16 V (decimal = 4000, hex = 0FA0), and LSB = 4 mV.
|Bit 1||Although the data from the last conversion can be read at any time, the INA219 Conversion Ready bit (CNVR) indicates when data from a conversion is available in the data output registers. The CNVR bit is set after all conversions, averaging, and multiplications are complete. CNVR will clear under the following conditions:
1.) Writing a new mode into the Operating Mode bits in the Configuration Register (except for Power-Down or Disable)
2.) Reading the Power Register
|OVF:||Math Overflow Flag|
|Bit 0||The Math Overflow Flag (OVF) is set when the Power or Current calculations are out of range. It indicates that current and power data may be meaningless.|
Full-scale range and LSB are set by the Calibration register. See the Programming the Calibration Register.
|LEGEND: R/W = Read/Write; R = Read only; -n = value after reset|
The Power register records power in watts by multiplying the values of the current with the value of the bus voltage according to the equation Equation 5:
Full-scale range and LSB depend on the value entered in the Calibration register. See Programming the Calibration Register for more information. Negative values are stored in 2's complement format.
|LEGEND: R/W = Read/Write; R = Read only; -n = value after reset|
The value of the Current register is calculated by multiplying the value in the Shunt Voltage register with the value in the Calibration register according to the Equation 4:
Current and power calibration are set by bits FS15 to FS1 of the Calibration register. Note that bit FS0 is not used in the calculation. This register sets the current that corresponds to a full-scale drop across the shunt. Full-scale range and the LSB of the current and power measurement depend on the value entered in this register. See the Programming the Calibration Register. This register is suitable for use in overall system calibration. Note that the 0 POR values are all default.
|LEGEND: R/W = Read/Write; R = Read only; -n = value after reset|