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I’m using ADM1087 and in general it works as expected.  However, the timing seems to shift dramatically from time to time and becomes somewhat unpredictable.

As attached, the circuit is to generate a 60-second delay.  What we are seeing is that it ranges from 40~65 seconds all in room temperature.  What makes it strange is the timing typically decreases from longer delay (65 sec the first operation) to shorter delay (40 sec after few operations).  The capacitors used are 10% tolerance (P/N shown below).



I understand the cap’s 10% tolerance can affect the initial timing, but can’t figure out why it changes over time.  Does the circuit require discharging the timing capacitor?


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