Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.
The TPS6217x is a high-efficiency synchronous step-down DC-DC converter, based on the DCS-Control topology.
With a wide operating input voltage range of 4.75 V to 28 V, the device is ideally suited for systems powered from multi cell Li-Ion as well as 12 V and even higher intermediate supply rails, providing up to 500-mA output current.
The device operates for an input voltage range of 4.75 V to 28 V. The output voltage is adjustable, using an external resistive divider, or internally fixed.
|IC||28 V, 0.5-A Step-Down Converter, WSON||TPS62175DQC, Texas Instruments|
|L1||10 uH, (4 × 4 × 1.2) mm||LPS4012, Coilcraft|
|Cin||2.2 µF, 50 V, Ceramic, 0805, X5R||Standard|
|Cout||22 µF, 6.3 V, Ceramic, 0805, X5R||Standard|
|R1||depending on VOUT|
|R2||depending on VOUT|
|R3||100 kΩ, Chip, 0603, 1/16 W, 1%||Standard|
While the output voltage of the TPS62175 is adjustable, the TPS62177 is programmed to a fixed output voltage of 3.3 V. For the fixed output voltage version, the FB pin is pulled low internally by a 400-kΩ resistor. TI recommends connecting the FB pin to AGND to improve thermal resistance. The adjustable version can be programmed for output voltages from 1 V to 6 V by using a resistive divider. The voltage at the FB pin is regulated to 800 mV. The value of the output voltage is set by the selection of the resistive divider from Equation 5. TI recommends choosing resistor values that allow a current of at least 5 uA. Lower resistor values are recommended to increase noise immunity. For applications requiring lowest current consumption, the use of the fixed-output voltage version is recommended.
As a safety feature, the device clamps the output voltage at the VOS pin to typically 7.4 V, if the FB pin gets opened.
The external components must fulfill the needs of the application, but also the stability criteria of the device's control loop. The TPS6217x is optimized to work within a wide range of external components. The LC output filter's inductance and capacitance must be considered together, creating a double pole that is responsible for the corner frequency of the converter. Table 2 shows the recommended output filter components.
|10 µF||22 µF||47 µF||100 µF||200 µF||400 µF|
The TPS6217x devices are internally compensated and are stable with LC output filter combinations recommended in Table 2. Further information on other values and loop stability can be found in Optimizing the TPS62175 Output Filter (SLVA543).
The inductor selection is determined by several effects like inductor ripple current, output ripple voltage, PWM-to-Power Save Mode transition point and efficiency. In addition, the inductor selected must be rated for appropriate saturation current and DC resistance (DCR). Equation 6 and Equation 7 calculate the maximum inductor current under static load conditions.
Calculating the maximum inductor current using the actual operating conditions gives the minimum saturation current of the inductor needed. TI recommends a margin of about 20% to cover possible load transient overshoot. A larger inductor value is also useful to get lower ripple current, but increases the transient response time and solution size as well. The inductors listed in Table 3 have been tested with the TPS6217x.
|TYPE||INDUCTANCE (µH])||CURRENT (A)(1)||DCR (mΩ)||DIMENSIONS (LENGTH x WIDTH x HEIGHT) mm||MANUFACTURER|
|LPS4012-103MLC||10 µH, ±20%||1.1||350 (maximum)||4 x 4 × 1.2||Coilcraft|
|LPS4018-103MLC||10 µH, ±20%||1.3||200 (maximum)||4 x 4 × 1.8||Coilcraft|
|VLS4012ET-100M||10 µH, ±20%||0.99||190 (typical)||4 x 4 × 1.2||TDK|
|VLCF4020T-100MR85||10 µH, ±20%||0.85||168 (typical)||4 × 4 × 2||TDK|
|74437324100||10 µH, ±20%||1.5||215 (typical)||4.5 × 4.1 × 1.8||Wuerth|
|744025100||10 µH, ±20%||1||190 (maximum)||2.8 × 2.8 × 2.8||Wuerth|
|IFSC-1515AH-01||10 µH, ±20%||1.3||135 (typical)||3.8 × 3.8 × 1.8||Vishay|
|ELL-4LG100MA||10 µH, ±20%||0.8||200 (typical)||3.8 × 3.8 × 1.8||Panasonic|
The recommended value for the output capacitor is 22 uF. To maintain low output voltage ripple during large load transients, for output voltages less than 2 V, TI recommends 2 × 22 µF output capacitors. The architecture of the TPS6217x allows the use of ceramic output capacitors with low equivalent series resistance (ESR). These capacitors provide low output voltage ripple and are recommended with an X7R or X5R dielectric. Larger capacitance values have the advantage of smaller output voltage ripple and a tighter DC output accuracy in power save mode.
In power save mode, the output voltage ripple and accuracy depends on the output capacitance and the inductor value. The larger the capacitance the lower the output voltage ripple and the better the output voltage accuracy. The same relation applies to the inductor value.
Typically, 2.2 µF is sufficient and is recommended, though a larger value reduces input current ripple further. The input capacitor buffers the input voltage during transient events and also decouples the converter from the supply. TI recommends a low ESR, multilayer, X5R or X7R dielectric, ceramic capacitor for best filtering, which should be placed between VIN and PGND as close as possible to those pins.
DC Bias effect: High capacitance ceramic capacitors have a DC Bias effect, which has a strong influence on the final effective capacitance. Therefore, the right capacitor value must be chosen carefully. Package size and voltage rating in combination with dielectric material are responsible for differences between the rated capacitor value and the effective capacitance.
The TPS6217x can be used advantageously as the power supply rail for microcontrollers with low current power save modes. Figure 54 shows the connection of TPS62177 to the Tiva C Series TM4C123x ARM Cortex™ - M4 MCUs (TM4C123x MCUs), using its hibernate mode signal to control sleep mode operation. More information is found in the Application Report, Powering Tiva™ C Series Microcontrollers Using the High Efficiency DCS-Control™ Topology (SPMA066).
The TPS6217x can be used as inverting power supply by rearranging external circuitry as shown in Figure 55. As the former GND node now represents a voltage level below system ground, the voltage difference between VIN and VOUT must be limited to the maximum operating voltage of 28 V.
More information about using TPS62175 as inverting buck-boost converter can be found in the Application Note, Using the TPS62175 in an Inverting Buck Boost Topology (SLVA542).
The following example circuits show typical schematics for commonly used output voltage values using the adjustable device version TPS62175.
The following example circuit shows the typical schematic for fixed output voltage using the device version TPS62177.