ZHCSPC5 October 2022 LM51231-Q1
PRODUCTION DATA
When UVLO is greater than the UVLO threshold (VUVLO), the device enters active mode if the device configuration is finished. UVLO hysteresis is accomplished with an internal 25-mV voltage hysteresis (VUVLO-HYS) at the UVLO pin, and an additional 10-μA current sink (IUVLO-HYS) that is switched on or off. When the UVLO pin voltage exceeds VUVLO, the current sink is disabled to quickly raise the voltage at the UVLO pin. When the UVLO pin voltage falls below VUVLO or during the device configuration time, the current sink is enabled, causing the voltage at the UVLO pin to fall quickly.
The external UVLO resistor voltage divider (RUVLOT, RUVLOB) must be designed so that the voltage at the UVLO pin is greater than VUVLO when VSUPPLY is in the desired operating range. The values of RUVLOT and RUVLOB can be calculated as follows.
A UVLO capacitor (CUVLO) is required in case VSUPPLY drops below VSUPPLY-OFF momentarily during the start-up or during a severe load transient at the low input voltage. If the required UVLO capacitor is large, an additional series UVLO resistor (RUVLOS) can be used to quickly raise the voltage at the UVLO pin when IUVLO-HYS is disabled.
The UVLO pin can be connected to the BIAS pin if not used. Drive the UVLO pin through a minimum of a 5-kΩ resistor if the BIAS pin voltage is less than the UVLO pin voltage in any conditions.