ZHCSJO3A May 2019 – October 2019 LMR34215-Q1
The output voltage of LMR34215-Q1 is externally adjustable using a resistor divider network. The range of recommended output voltage is found in the Electrical Characteristics table. 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 resistance of the divider is a compromise between excessive noise pick-up and excessive loading of the output. Smaller values of resistance reduce noise sensitivity but also reduce the light-load efficiency. The recommended value for RFBT is 100 kΩ; with a maximum value of 1 MΩ. If a 1 MΩ is selected for RFBT, then a feed-forward capacitor must be used across this resistor to provide adequate loop phase margin (see CFF Selection). Once RFBT is selected, Equation 3 is used to select RFBB. VREF is nominally 1 V.
For example, the 5-V output values are: RFBT = 100 kΩ and RFBB = 24.9 kΩ.