Accurate OP AMP at DC with low offset

Anthony Smith57

Other Parts Discussed in Thread: OPA188, OPA189, OPA333, OPA191, OPA192, TLV2333

I have a circuit and am looking for an accurate opamp with low offset, the circuit measures the current in R13, multiplies it by 101 and presents a dc value between 0 and 3.3v for 0 to 33mA through R13,

Can anybody recommend an op amp for the jobAux In.pdf

over 4 years ago

0 Raymond Zhang1 over 4 years ago

TI__Guru 54111 points

Hi Anthony,

Are there any slew rate requirements? TI has many such selections to meet the above requirements, such as OPA192, OPA191, OPA188, OPA189, OPA333, TVL333, that come to mind. I see that your BW is low in the attached schematic.

Best,

Raymond

0 Anthony Smith57 over 4 years ago in reply to Raymond Zhang1

Prodigy 60 points

Thanks, the TLV2333 looks ideal

0 kai klaas69 over 4 years ago in reply to Anthony Smith57

Guru 140200 points

Hi Anthony,

I would remove C40 :-)

Kai

0 Anthony Smith57 over 4 years ago in reply to kai klaas69

Prodigy 60 points

why? it lowers bandwidth and provides immunity to emc?

0 kai klaas69 over 4 years ago in reply to Anthony Smith57

Guru 140200 points

Hi Anthony,

Your scheme shows this non-inerting amplifier:

anthony_tlv333.TSC

C2 (in the simulation) introduces a massive phase lag in the feedback loop which erodes the phase margin of OPAmp. This causes instability and oscillation.

Kai

0 Anthony Smith57 over 4 years ago in reply to kai klaas69

Prodigy 60 points

Thanks, I had been obsessed with band width and stable measurements, I completely ignored phase margin!

0 kai klaas69 over 4 years ago in reply to Anthony Smith57

Guru 140200 points

Good luck, Anthony :-)

Kai

0 Anthony Smith57 over 4 years ago in reply to kai klaas69

Prodigy 60 points

Thanks- its all working!

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Accurate OP AMP at DC with low offset