My customer is using a pull-down circuit on the output that essentially looks like a 60kohm load in parallel with the Load (3ohm). This 60kohm circuit is used for a separate power good indicator circuit. The ST pin (Version A) goes low during an open load condition without the external pull-up, which is recommended in the datasheet. They are using 12V on Vs.
We are curious why the circuit is operating correctly without the recommended pull-up resistor?
ON-State Open-Load: 12V(on-state; OUT=H)/60k = 200uA, which is less than Iol,on (2mA-10mA) and would result in ST=Low.
What would be the result in an off-state situation (Vin=Low)?
There could be an RC time constant that is taking about 800us (600us = nom time in off state to trigger the open load detection) to discharge Vout to 10.2V (Vs-Vout=1.8V; this is the nom threshold for open load detection in the off-state).
Is this implementation okay and should we be concerned with any corner cases that might cause the device to diagnose faults or function improperly?
Cheers,
Joe
