If other voltages are desired, the VOUT/FB pin can be connected to a feedback resistor divider network to set the output voltage. The divider network is comprised of RFBT and RFBB, and closes the loop between the output voltage and the converter. The converter regulates the output voltage by holding the voltage on the FB pin equal to the internal reference voltage, VREF. The converter determines whether fixed output voltage or adjustable output voltage is required by sensing the resistance of the feedback path during start-up. To ensure that the converter regulates to the desired output voltage, the typical minimum value for the parallel combination of RFBT and RFBB is 5 kΩ while the typical maximum value is 10 kΩ as shown in Equation 5. Equation 6 can be used as a starting point to determine the value of RFBT. Reference Table 9-4 for a list of acceptable resistor values for various output voltages.
|VOUT (V)||RFBT (1) (kΩ)||RFBB (kΩ)|
For this 3.3-V example, the user can choose the LMR43620MSC3RPERQ1 and connect the VOUT/FB pin directly to the output capacitor.