ZHCSQT8 October 2023 LM74930-Q1
PRODUCTION DATA
Resistors R1, R2 and R3, R4 connected from SW pin to ground is used to program the undervoltage and overvoltage threshold. The resistor values required for setting the undervoltage threshold (VUVLO to 5.5 V) and overvoltage threshold (VOV to 37.0 V) a are calculated by solving
For minimizing the input current drawn from the battery through resistors R1, R2, and R3, R4; TI recommends to use higher value of resistance. Using high value resistors adds error in the calculations because the current through the resistors at higher value becomes comparable to the leakage current into the OV pin. Maximum leakage current into the UVLO and OV pin is 0.2 μA and choosing total ladder resistor in 100kΩ range ensures current through resistors is much higher than leakage through the OV pin.
Based on the device electrical characteristics, VUVLOF is 0.55 V. Select R1 = 100 kΩ. Solving Equation 12 gives R2 = 11.5 kΩ. Solving Equation 13 with R3 selected as 100 kΩ and VOVR = 0.6 V gives R4 = 1.65 kΩ as standard 1% resistor values closest to the calculated resistor values.
An optional capacitor CUV can be placed in parallel with R2 on UVLO resistor ladder to filter out any fast undervoltage transients on battery lines to avoid false UVLO trigger.