Within the TPS6120X family, there are fixed and adjustable output voltage versions available. To properly configure the fixed output voltage devices, the FB pin is used to sense the output voltage. This means that it must be connected directly to VOUT. For the adjustable output voltage version, an external resistor divider is used to adjust the output voltage. The resistor divider must be connected between VOUT, FB and GND. When the output voltage is regulated properly, the typical value of the voltage at the FB pin is 500 mV. The maximum recommended value for the output voltage is 5.5 V. The current through the resistive divider should be about 100 times greater than the current into the FB pin. The typical current into the FB pin is 0.01 μA, and the voltage across the resistor between FB and GND, R2, is typically 500 mV. Based on those two values, the recommended value for R2 should be lower than 500 kΩ, in order to set the divider current at 1 μA or higher. It is recommended to keep the value for this resistor in the range of 200 kΩ. The value of the resistor connected between VOUT and FB, R1, depending on the needed output voltage (V_OUT), can be calculated using Equation 1:

Equation 1.

As an example, for an output voltage of 3.3 V, a 1-MΩ resistor should be chosen for R₁ when a 180-kΩ is selected for R₂.

Table 3. List of Inductors

11.2.2.4.1 Input Capacitor

At least a 4.7-μF input capacitor is recommended to improve transient behavior of the regulator and EMI behavior of the total power supply circuit. An X5R or X7R ceramic capacitor placed as close as possible to the VIN and PGND pins of the IC is recommended.

An R-C filter may be placed on the VIN pin to improve performance in applications with a noisy input source. A 100-Ω resistor and 0.1-µF capacitor are recommended in this case. This filter is not required operation.

11.2.2.4.2 Output Capacitor

For the output capacitor, it is recommended to use small X5R or X7R ceramic capacitors placed as close as possible to the VOUT and PGND pins of the IC. If, for any reason, the application requires the use of large capacitors which can not be placed close to the IC, using a smaller ceramic capacitor in parallel to the large one is required. This small capacitor should be placed as close as possible to the VOUT and PGND pins of the IC.

To get an estimate of the recommended minimum output capacitance, Equation 5 can be used.

Equation 5.

A capacitor with a value in the range of the calculated minimum should be used. This is required to maintain control loop stability. There are no additional requirements regarding minimum ESR. There is also no upper limit for the output capacitance value. Larger capacitors cause lower output voltage ripple as well as lower output voltage drops during load transients.

11.2.2.4.3 Capacitor at VAUX

Between the VAUX pin and GND pin, a capacitor must be connected. This capacitor is used to maintain and filter the control supply voltage, which is chosen from the highest of VIN, VOUT, and L. It is charged during startup and before the main output VOUT is turned on. To ensure stable operation, using at least 0.1μF is recommended. At output voltages below 2.5 V, the capacitance should be in the range of 1 μF. Since this capacitor is also used as a snubber capacitor for the main switch, using a X5R or X7R ceramic capacitor with low ESR is important.