JAJSJT8C May 2020 – June 2021 TPS543620
The undervoltage lockout (UVLO) is adjusted using the external voltage divider network of RENT and RENB. The UVLO has two thresholds: one for power up when the input voltage is rising and one for power down or brownouts when the input voltage is falling. For the example design, the supply is set to turn on and start switching once the input voltage increases above 4.5 V (UVLO start or enable). After the regulator starts switching, it continues to do so until the input voltage falls below 3.95 V (UVLO stop or disable). In this example, these start and stop voltages set by the EN resistor divider were selected to have more hysteresis than the internally fixed VIN UVLO.
Equation 1 and Equation 2 can be used to calculate the values for the upper and lower resistor values. For these equations to work, VSTART must be 1.1 × VSTOP due to the EN pin's voltage hysteresis. For the voltages specified, the standard resistor value used for RENT is 16.9 kΩ and for RENB is 6.04 kΩ.