The output voltage is set with a single external resistor connected between the VSET pin and GND. After the device has been enabled and the control logic as well as the internal reference have been powered up, a R2D (resistor-to-digital) conversion is started to detect the external resistor, R_SET, within the regulator start-up delay time, t_{Startup_delay}. An internal current source applies current through the external resistor and an internal ADC reads back the resulting voltage level. Depending on the level, an internal feedback divider network is selected to set the correct output voltage. After this R2D conversion is finished, the current source is turned off to avoid current flow through the external resistor. The circuit can detect resistive values, high-level, low-level, and a pin-open.

For a proper reading, make sure that there is no additional current path or capacitance greater than 30pF total to GND during R2D conversion. Otherwise, the additional current to GND is interpreted as a lower resistor value and a false output voltage is set. Table 7-1 lists the correct resistor values for R_SET to set the appropriate output voltages. The R2D converter is designed to operate with resistor values out of the E96 table and requires 1% resistor value accuracy. The external resistor R_SET is not a part of the regulator feedback loop and has therefore no impact on the output voltage accuracy. Make sure that there is no other leakage path than the R_SET resistor at the VSET pin during an undervoltage lockout event. Otherwise, a false output voltage is set.