JAJSH44C April 2011 – March 2019 UCD90120A
Open-loop margining is done by connecting a power-supply feedback node to ground through one resistor and to the margined power supply output (VOUT) through another resistor. The power-supply regulation loop responds to the change in feedback node voltage by increasing or decreasing the power-supply output voltage to return the feedback voltage to the original value. The voltage change is determined by the fixed resistor values and the voltage at VOUT and ground. Two GPIO pins must be configured as open-drain outputs for connecting resistors from the feedback node of each power supply to VOUT or ground.