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I read ADS7961 datasheet which mentioned input capacitor is 15pF.
My first problem is that 15pF.
Is the 15pF MXO input or AINP?
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Beside, my ADC driver is non-inverting amplifier.
I'm considering about overshoot problem because ADC is capacitive load.
I hope:
* Direct drive ADC without Riso. That means direct short MXO and AINP, but MXO input will be drived by OPA172 or OPA192
* Overshoot < 10Vp
I read OPA172 datasheet
and OPA192 datasheet
I think select OPA192 can direct drive ADS7961, is right?
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My circuit:
Photodiode -> OPA810(I/V Converter) -> OPA172(Integrator) -> OPA192(ADC Driver) -> ADS7961(ADC)
DeWei,
Best regards,
Art
Many thanks Art Kay detailing reply:
My fully circuit block diagram as here
(1) Many thanks! I found this useful picture
(2) Yes, I'd place OPA192 between MXO and AINP as ADC driver
(3) Actually, >=10KHz sample on per channels is enough for my usage.
If sample rate is as low as 10KHz, should I need care about “settling error”?
(4) Integrator also drags detected pulse(width = 10us ~ 500us) to 1 ~ 10 ms
(5) My system adopt +5V single rail PSU(USB Vbus as PSU).
Our refer to here
(6) OPA192 and OPA172 are remaining components in my last project, but OPA320 looking like a good choice if I have not enough
OPA192 and OPA172
DeWei,
Best regards,
Art
Oh! My bad!
I discover Rail-to-Rail of OPA172 only guarantee output instead of both input and output.
So I'd not adopt OPA172.
The reason for selecting OPA172 is also because of the cost.
But for the cost reason, I think OPA325 is a good choice, because OPA325 not only cheap but also provide Rail-to-Rail both I/O.
I'll also check our stock if OPA192 is enough for replacing OPA172.
Anyway, thank you very much for your very useful suggestion.