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ADS7828 Abs Max for Analog inputs

James Long
Prodigy 150 points
Other Parts Discussed in Thread: ADS7828

I'm using the ADS7828 in a new design where there may be voltage present on the analog inputs before the device is powered.

The voltage on the inputs will have a high source impedance and will not exceed the measurement range of the device, but it could be in this state for upto one second before the chip is fully powered up.

Whilst the Abs max section of the datasheet doesn't lists a spec for the analog inputs, the electrical characteristics section has a line for "Analog input: Absolute input range" being between -0.2 and +Vdd+0.2V. This implies that it's not okay to exceed the supply rail, but is it okay to do this for a short time as long as the current into the (presumably shottky-clamped) pin is less than a certain amount?

Thanks

James.

  • 0
    TI__Guru**** 180931 points

    Hi James,

    The MAX voltage specified to the input of the ADS7828 is actually a little conservative - at about +/-300mV over the rail voltages, the internal ESD cells will start to conduct.  In general, we try to discourage the application of an analog input voltage that exceeds the power rails - we can't really give you a long term device reliability statement when operated that way.  If you use external protection diodes which clamp the voltage, that will help to prevent permanent damage to the ADS7828.