SBVS336A September 2021 – May 2022 TPS7A94
The precision enable circuit is used to turn the device on and off. This circuit can be used to set an external undervoltage lockout (UVLO) voltage (see Figure 8-6) to turn on and off the device using a resistor divider between IN, EN_UV, and GND.
If VEN_UV ≥ VIH(EN_UV), the regulator is enabled. If VEN_UV ≤ VIL(EN_UV), the regulator is disabled. The EN_UV pin does not incorporate an internal pulldown resistor to GND and must not be left floating. Use the precision enable circuit for this pin to set an external undervoltage lockout (UVLO) input supply voltage to turn on and off the device using a resistor divider between IN, EN_UV, and GND.
This external UVLO solution is used to prevent the LDO from turning on when the input supply voltage is insufficient and places the device in dropout operation.
Using the EN_UV pin as an externally set UVLO allows simple sequencing of cascaded power supplies. An additional benefit is that the EN_UV pin is never left floating. The EN_UV pin does not have an internal pulldown resistor. In addition to the resistor divider, a zener diode may be needed between the EN_UV pin and ground to comply with the absolute maximum ratings on this pin.
Consider the EN_UV current pin when selecting the R(TOP) and R(BOTTOM) values.