AD6645: Max input signal

Document created by analog-archivist Employee on Feb 23, 2016
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please can you tell me how the AD6645 will cope with a continuous sin wave
signal applied between the Full scale maximum and the absolute maximum input
rating of the device. We have an error mode where this may occur and I would
like to know if continuous exposure to this level of signal could damage the
device or cause it to go into thermal shutdown. Does the device have thermal
protection?

 

If you have a continuous sine wave applied differentially to the device
centered around 2.4V, whose amplitude is greater than 2.2V p-p (> 1.1V p-p in
antiphase on each input) then you will see clipping on the output signal and
the overrange bit will become active. There will be no damage to the chip as
long as the voltages on each input do not exceed the power supplies. The worst
case is if one input is at 5V and the other at GND. This would give 5mA input
current which is within the abs max ratings of the device.

If the absolute input voltage either input exceeds the power supplies then the
ESD protection diodes will turn on  (see figure 2 in the datasheet showing the
equivalent circuit for the analog input). Once these diodes turn on they will
begin to conduct significant amounts of current which, if not externally
limited will cause electrical or thermal damage to the IC.

The device has no thermal protection which would protect it from an input
overvoltage condition.

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