Pro Fet ITS428 ST Pin False Fault Indication for Low Load Current

[Tim_Dunn]

Trying to use the ST pin of ITS428L2ATMA1 to report fault by sinking from a +5.5V supply above the source through 560 ohms and the LED of an optocoupler. 

I find at the ON state (Vgs = +5.5V), that loads below 0.25A cause a false fault as the ST pin sinks to 1.05V. 

For loads above 0.25A the pin sits at 4.85V as expected. 

If I increase the 560 ohms to 1100 ohms, this threshold load current raises to about 0.28A, and faults are reported below that.

[Anshika_G]

Hello @Tim_Dunn ,

ITS428L2  is a high side power switch providing embedded protection and diagnostic functions.
It has a current limitation of :

I am not able to fully understand your question because ILS428 has current limit of typically 22 A and from the query what I have understood is that you are experiencing false overcurrent detection at loads below 0.25 A.

Can you please elaborate a little more(maybe share your schematic, waveforms, measurement results)?

Thanks and Regards,
Anshika

[Tim_Dunn]

Thanks,  Attaching a schematic showing 1 of 4 output circuits per common group for this 16 point PLC sourcing (High Side Switching) Output module (5-36VDC).  The issue is a false report of a fault via the ST pin sinking current at about 1.0V for ON state loads less than 0.25A.  The output remains ON as expected during this condition.  The extra circuitry around the output is to add OFF state Open Load detection not provided by the ITS428.

[Anshika_G · Accepted solution]

Hi @Tim_Dunn ,

I have understood your question.  The open load detection current for ITS428 is in the range of 10mA to 500mA. It will detect the faults for load even for less than 250mA , i.e., 0.25A, since it is in the range.

Regards,
Anshika

[Tim_Dunn]

Understood.  The ST pin does not function as "Open Load" detect but rather "Light Load" detect.