# offset problem of AD8629 OPAMP

Our customer have met one trouble as following.

(This discuss came from another sled cause my miss understood)

On my enclosed schematic Fig-1.pdf,

step-1 power off and keep waiting around 30 sec

step-2 power on

step-3 around 90msec offset voltage appear at out-1 pin

step-4 power off and on but the 90mV offset is not cleared

Also refer to my enclosed time chart "tme chart when power off and on.pdf".

note

*1 ; 30sec is not certainly.

*3 ; in some cases, it return to expected value

After once this trouble happen, out-2 is up and dowm on offset voltage 900mV(x10 gained value)

When we work with above action, does your AD8629 do such a motion?or not.

If he replace the thermopile(TP) to fixed resister 175kohm, then the result was same.

Thank you in advance Kaos

attachments.zip
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• Hi Chard,

I confirmed as for your comment to our customer.

Your understanding is correct.

The voltage that is divided by 10kohm and 910ohm for 5V should be outputed gain1, and the potential difference between + and - pin of AD8629 should be amplified 3000 times and be outputed he think.

So here is 175kohm on TP, then the voltage that is divided by 10kohm and 910ohm for 5V should be outputed simply he think.

This problem didnt bring the expected result.

Why this 90mV is added??? Circuit design mistake??

step-3 around 90msec offset voltage appear at out-1 pin

===>sorry typo! 90mV not 90msec I correct.

Thanks Kaos

• Hi Chard,

I confirmed as for your comment to our customer.

Your understanding is correct.

The voltage that is divided by 10kohm and 910ohm for 5V should be outputed gain1, and the potential difference between + and - pin of AD8629 should be amplified 3000 times and be outputed he think.

So here is 175kohm on TP, then the voltage that is divided by 10kohm and 910ohm for 5V should be outputed simply he think.

This problem didnt bring the expected result.

Why this 90mV is added??? Circuit design mistake??

step-3 around 90msec offset voltage appear at out-1 pin

===>sorry typo! 90mV not 90msec I correct.

Thanks Kaos

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