SLVSDV8 July 2017 TPS54424
The Undervoltage Lockout (UVLO) is adjusted using the external voltage divider network of R2 (RENT) and R9 (RENB). The UVLO has two thresholds; one for power up when the input voltage is rising and one for power-down or brown outs when the input voltage is falling. For the example design, the supply should turn on and start switching once the input voltage increases above 4.5 V (UVLO start or enable). After the regulator starts switching, it should continue to do so until the input voltage falls below 4.0 V (UVLO stop or disable). Equation 2 and Equation 3 can be used to calculate the values for the upper and lower resistor values. For the voltages specified, the standard resistor value used for R2 is 86.6 kΩ and for R4 is 30.9 kΩ.