topic mc33908 reverse polarity in Other NXP Products

mc33908 reverse polarity

anzicek — Thu, 19 Jul 2018 16:07:47 GMT

#MC33908 - Hello, I am curious what continuous reverse polarity the MC33908 #Vsense pin can withstand. My implementation includes the external 5.1kOhm resistor, but the maximum ratings only show -14.0V as the max rating, no clamping voltage or current that the pin can withstand. If a current were provided I could calculate. There are also resistive dividers internal to the MC33908 on the Vsense pin, but the values of these are not given, again with the values of these, the -14V could be extrapolated to the input voltage with the 5.1k resistor.

Any help you can provide would be appreciated,

Thanks,

Josh

Re: mc33908 reverse polarity

TomasVaverka — Wed, 01 Aug 2018 10:19:03 GMT

Hi Joshua,

First off, sorry for the delay in answering your question.

The divider resistance value inside Vsense pin is MΩ level, so 5.1K has quite a little impact for Vsense pin voltage rating. -14V is maximum reverse voltage rating for both with or without 5.1K resistor .

Hope it answers your question.

Best regards,

Tomas

Re: mc33908 reverse polarity

anzicek — Wed, 01 Aug 2018 18:53:54 GMT

Hello Tomas, the issue I have is that there must be some current flow into the pin prior to breakdown. The pin clearly handles substantially greater voltages during the ISO 7637 tests (-100V and -150V or pulses 1 and 3a), so I'm trying to get a better understanding of the input architecture so I can defend our use case. I have test data that shows this device survives repeated exposure to more than -14V but I don't have an engineering defense for that.

Any insight you can provide is appreciated.

Thanks,

Josh