SNOSDE8A July 2023 – September 2023 LM74912-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 Equation 6 and Equation 6.
For minimizing the input current drawn from the battery through resistors R1, R2 and R3, it recommended to use higher value of resistance. Using high value resistors will add error in the calculations because the current through the resistors at higher value will become comparable to the leakage current into the OV pin. Maximum leakage current into the OV pin is 1 µA and choosing (R1 + R2 + R3) < 120 kΩ ensures current through resistors is 100 times greater than leakage through OV pin.
Based on the device electrical characteristics, VUVLOF is 0.55 V. Select R1 = 100 kΩ. Solving Equation 14 gives R2 = 11.5 kΩ. Solving Equation 15 with R3 selected as 100 kΩ and VOVR = 0.6V 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 in order to filter out any fast undervoltage transients on battery lines to avoid false UVLO trigger.
For this application example separate resistor ladder is selected to program overvoltage and undervoltage threshold. However common resistor ladder from SW pin to ground can also be used as shown in Section 8.3.4