AD7778: Input signal out of specified range

Document created by analog-archivist Employee on Feb 23, 2016
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If my AD-converter above is set to work within let's say 0-2 V, what happens
with the output signal (10 bits) if the input signal goes under 0 V or over 2
V? I couldn't find it in the data sheet. I guess the converted data is invalid
in some way, but how long does it take to get back to normal function? I mean,
let's say I have a glitch that goes under 0 V for a short period, is the data
that follows (when input is normal) valid or invalid?

 

Exceeding the input range of the AD7778 to within the absolute max limits of
the part...which are specified as
-0.3V to Vcc+0.3V will cause the o/p code to sit at either +ve or -ve
full-scale.
The input track and hold amplifier may saturate, however once the i/p voltage
returns to within the normal operating range, the track and hold amp will
acquire the new voltage in a time specified as the acquisition time..see page 2
of the datasheet.

Exceeding the max ratings of the ADC, may cause permanent damage to the device,
and if there is a possibility of this occuring, then the device should be
protected against this occurance.
One such method is to connect shottky diodes between the input pin and the
supplies, such that in the event of an overvoltage occurance, the input voltage
is clampled to 0.3V outside the supplies.
A series resistor should be included to limit the current in this condition.

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