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AMC7834: Is it safe to provide ADC inputs before powering the chip?

Lawrence Trevor1
Prodigy 90 points
Part Number: AMC7834

Hi,

I'm working with an implementation of this chip where there is a 'race condition' of sorts between the xVDD, AVCC and IOVDD pins, and the ADC MUX inputs. Basically, an unregulated supply is applied to the board, which is then regulated to power the AMC7834, but the AMC7834 is also connected to measure this unregulated supply through both its current and voltage mux inputs. This means that it is likely that voltage will be applied to these inputs before the AMC7834 is powered itself.

I couldn't see any specific mention of whether this was something to avoid, or not, in the data sheet, so I thought I would ask here if this was a problem.

Regards,

LT

  • +1
    TI__Guru 53773 points

    Hi LT,

    It is possible to bias the ESD protection diodes if the inputs exceed 0.3V+AVDD.  These diodes can get damaged if high-current is sustained.  The current shunt inputs have a higher rating, so those are not at risk.

    Thanks,

    Paul

  • 0 in reply to Paul_Frost
    Prodigy 90 points

    Hi Paul,

    I think I found the section for what you explained:


    Before AVdd was supplied, the high side diode would switch at anything above 0.3 V. Given my voltage divider at the adc input, this would be likely given the voltage I am measuring. I'll have to put some time into analysing whether that is safe to do, but thanks for pointing me in the right direction.