SNVSCW3 November 2024 LM644A2-Q1
PRODUCTION DATA
The output regulation target can be programmed to a fixed 3.3V by connecting FB to AGND, or a fixed 5.0V output by connecting FB to VCC through a 10kΩ resistor. Also, the output voltage of the LM644A2-Q1 is externally adjustable using a resistor divider network. The divider network is comprised of the top and bottom feedback resistors, RFBT and RFBB, and closes the loop between the output voltage and the converter. The converter regulates the output voltage by holding the voltage at the internal error amplifier input equal to the internal reference voltage, VFB = 0.8V. The total resistance of the divider is a compromise between excessive noise pickup and excessive loading of the output. Lower resistance values reduce noise sensitivity but also reduce the light-load efficiency. The recommended value for RFBT is around 100kΩ with a maximum value of 1MΩ.