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ADS1293: Model for input ESD protection

Mark 6
Prodigy 10 points
Part Number: ADS1293

Having killed a couple of ADS1293 chips during development, I'm concerned about possible latch-up and/or power feed-through via the electrode input ESD protection diodes.  The failed devices exhibit a very low resistance between the analog Vdd and Vss pins.

I suspect voltages in the +/- 20 Volt range may have been present on INx input pins both before and during power-up.

The datasheet lists absolute maximum ratings for the input pins, but no explanation of behaviour outside this voltage range, other than the ESD ratings for much higher transient voltages

Is there a Spice model of the input protection structures?

Alternatively, are there any specifications for maximum tolerable input pin current under such fault conditions, or recommendations on preventing damage (I already have 10k in series with each input to limit current, but no other external protection circuitry) ?

  • 0
    TI__Mastermind 38745 points
    Hey Mark,

    Unfortunately we do not have a SPICE model for behavior of the overvoltage/ESD circuitry. The reason we do not spec behavior over the absolute maximums is that the manufacturing process is only capable of creating devices that meet a certain minimum durability to excessive stress. Device behavior over those specifications is extremely unpredictable and TI has decided to end its warranty at those specifications. You have to "draw the line" somewhere and that is just where TI has chosen to draw it.

    The ESD protection circuitry on the device can be thought of as a "last line of defense" in terms of protecting the device. It is extremely common in biomedical applications (and in several other types of applications where the inputs could come into contact with statically charged materials) for there to be additional input protection circuitry. This can be as simple as diodes that will conduct when the input voltage exceeds a few hundred millivolts from the rail and current limiting resistors.

    Regards,
    Brian Pisani