MC33814 diagnosis problem

[alessandrocorti]

Hello, I'm using the KIT33814AEEVBE kit to evaluate the MC33814 IC.

I have noted that if I switch on the outputs (INJ1, RELAY1, RELAY2 etc) with the OL Current Sink Enable bit for that outputs set (default), a short circuit to GND (SG) fault is arised and can't be deleted by writing to the relative status register until the OL Current Sink Enable bit is cleared (while the fault is not yet deleted), then the fault can be deleted.

Moreover, if the OL Current Sink Enable bit is cleared and the output is activated, the fault doesn't arise, but in this scenario, if the OL Current Sink Enable bit is set (while the outputs is on), then again the SG fault is arised.

It seems to me that isn't possible to have the OL Current Sink Enable bit set whit the output on.

Is this correct? am I missing something?

Should this be correct, have I to manually clear/set the OL Current Sink Enable bit before/after switch on/off the output?

Thank a lot,

Regards

[alessandrocorti]

Hello Tomas,

thank you so much for your precious answer, now I know how the diagnosis circuitry works.

For your informaion, I connected an automotive relay to the RELAY1 output (nearly 150 mA load) and the SG fault is rised again (with the OL current sink bit settled), but this time, the fault can be deleted.

Then I disconnected the relay and connected a resistive load ( nearly 900 mA ) and all worked as expected, no SG fault also with the OL current sink bit settled.

Thank you so much again,

Best regards.

Alessandro.

[TomasVaverka · Accepted solution]

Hello Alessandro,

There is an application note AN12226 dedicated to the diagnostics.

The part 3.1 explains how the SCG (open load ON state) is working.

Basically, if there is not enough current flowing through the low side driver, a short to ground can be detected. In our EVB, the load is made of LEDs, so not enough current is flowing. To really check this feature additional load must added on the corresponding LSD. The OL current sink bit both disables the internal pull-down and avoid SCG on LSD.

Best regards,

Tomas