SNVSC75 april 2023 LM5171-Q1
ADVANCE INFORMATION
The example circuit uses UVLO pin as the Controller enable pin of LM5171-Q1. However, UVLO pin can also fulfill the function of undervoltage lockout, either the 48-V rail UVLO, or 12-V rail UVLO, or VCC UVLO.
Assume the user implements the 48-V rail UVLO, and the low-side resistor RUVLO2 = 10 kΩ, the 48 V UVLO release threshold VUVLO = 24 V, and UVLO hysteresis is VHYS =2.4 V. Referring to Figure 7-32 and Equation 20, one can find that RUVLO1 is given by:
The final selection must select the closest standard resistor of RUVLO1 = 86.6 kΩ.
And RUVLO3 must satisfy Equation 22, namely,
Select the closest standard resistor, RUVLO1 = 976 Ω.
If the user chooses to add the capacitor CUVLO = 1 nF, it leads to a delay time constant of 10 µs to filter possible noise at the at the UVLO pin.