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 (V_UVLO to 5.5 V) and overvoltage threshold (V_OV to 37.0 V) a are calculated by solving

Equation 14.

Equation 15.

For minimizing the input current drawn from the battery through resistors R₁, R₂, and R₃; it is 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 total ladder resistor < 120 kΩ ensures current through resistors is 100 times greater than leakage through OV pin.

Based on the device electrical characteristics, V_UVLOF 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 V_OVR = 0.6 V gives R₄ = 1.65 kΩ as standard 1% resistor values closest to the calculated resistor values.

An optional capacitor C_UV 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 Figure 9-9.