ZHCSL19C May 2019 – June 2021 LM61440
PRODUCTION DATA
The output voltage of LM61440 is externally adjustable using a resistor divider network. The range of recommended output voltage is found in Section 7.3. 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 pickup 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 1 MΩ is selected for RFBT, then a feedforward capacitor must be used across this resistor to provide adequate loop phase margin (see Section 9.2.2.10). Once RFBT is selected, Equation 3 is used to select RFBB. VREF is nominally 1 V. For this 5-V example, RFBT = 100 kΩ and RFBB = 24.9 kΩ are chosen.