LM74703-Q1 and LM74704-Q1 have FETGOOD pin, which can be used to detect external MOSFET health, such as in cases where a MOSFET is short or open. The device monitors the external MOSFET source to drain voltage drop to decide MOSFET status as either MOSFET open or MOSFET short condition. The FETGOOD pin is pulled low whenever a MOSFET fault condition is detected.

MOSFET source to drain short detection is performed and status is indicated at each start-up event (ANODE ramp-up or EN pin going from low to high). For MOSFET source to drain short detection to work correctly, the device ANODE pin voltage must be 200 mV higher than the CATHODE pin voltage before performing external MOSFET short diagnosis.

For ideal diode configuration when the controller is off, output loads are always powered through the body diode of the external MOSFET. Detecting if the external MOSFET is completely turned-on or not before turning on downstream loads is important for avoiding large currents flowing through the body diode of MOSFET, which can potentially damage the MOSFET. This condition can arise due to gate voltage not getting applied to the MOSFET gate pin under specific fault condition, such as a MOSFET gate pin open due to a PCB manufacturing defect. LM74703-Q1 and LM74704-Q1 monitor external MOSFET source-to-drain drops and pulls the FETGOOD pin low if this drop is higher than 200 mV, even when the gate voltage is applied to the MOSFET. This behavior helps the system to monitor the MOSFET off condition during start-up (even when ideal diode controller is enabled) and indicate the MOSFET open fault using FETGOOD pin so that a decision on system level can be taken to turn off downstream loads to avoid large load current flowing through the body diode of the MOSFET. MOSFET open detection is available during device start-up as well as during normal operation.

The FETGOOD pin is also pulled low if the charge pump voltage is lower than the charge pump UVLO threshold of 6.6 V indicating gate drive voltage is not enough to fully enhance the MOSFET.

LM74703-Q1 has a push-pull FETGOOD output to support systems where there are not external pullups or bias voltages available when the system starts-up.

LM74704-Q1 has an open-drain FETGOOD output. The FETGOOD pin must be pulled to an external bias voltage through a pullup resistor. The external pullup resistor must be selected such that current through the FETGOOD pulldown switch is less than 1-mA to stay within the recommended operating conditions.

When not used, the FETGOOD pin must be left floating.