LM749x0-Q1 provides programmable overcurrent threshold setting by means of resistor (R_LIM) connected from I_LIM pin to GND.

Equation 3.

where

• R_SET is the resistor connected across CS+ and VS
• R_SNS is the current sense resistor
• I_LIM is the overcurrent level

The C_TMR programs the circuit breaker and auto-retry time. Once the voltage across CS+ and CS– exceeds the set point, the C_TMR starts charging with 85-µA pull up current. Once the C_TMR charges to V_{TMR_FLT}, FLT asserts low providing warning on impending FET turn OFF. Once C_TMR charges to V_{TMR_OC}, HGATE is pulled to OUT turning OFF the HFET. After this event, the auto-retry behavior starts. The C_TMR capacitor starts discharging with 2.7-µA pull down current. Once the voltage reaches VTMR_Low level, the capacitor starts charging with 2.7-µA pull up. After 32 charging/discharging cycles of C_TMR, the FET turns ON and FLT de-asserts after de-assertion delay.

Equation 4.

where

• T_OC is the delay to turn OFF the FET
• C_TMR is the capacitance across TMR to GND

The auto-retry time can be computed as

Equation 5.

If the overcurrent pulse duration is below T_OC then the FET remains ON and C_TMR gets discharged using internal pull down switch.

When not used, ILIM is connected to ground while TMR can be left floating.

Figure 9-3 LM749x0 Auto Retry TIMER Functionality

Figure 9-4 Overcurrent Protection With Auto Retry Timing Diagram

If the overcurrent pulse duration is below T_OC then the HFET remains ON and C_TMR gets discharged using internal pull down switch.