OPA2192: OPA2192 to replace ADA4077 have testing issue

Chao Fu Chen

Part Number: OPA2192

Hi team,

My customer wonder use our part to replace the ADA4077, but his component test team highlight our part have gap and failed this test cannot to directly to change.

The test is

Following the picture is his Voffset setting test condition , our gap is the secondary output will ringing , but competitor will not to see.

I try to change the Rf value to bigger and lower even add the RC on secondary amps output , but it still have no any help to fix.

I know this setting seems not really for Voffest checking , but our customer wonder to keep this setting to test the Voffset.

Because if we wonder to replace ADI , we also need to pass this setting condition is fair and the same level to compare performance.

Could you have any idea can share for me to turning in this case to fix it ?

Eddie

over 4 years ago

0 kai klaas69 over 4 years ago

Guru 140200 points

Hi Eddie,

I don't like this test circit because it's very hard to make it run stably.

Kai

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

Guru 140200 points

Hi Eddie,

I did some maths. It turns out that the loop amplifier isn't necessary here because the input offset voltage of OPA2192 is ultra low and the DC open loop gain is ultra high. So there is no need to bring the output voltage of OPA2192 fully down to 0V by the help of a loop amplifier :-)

eddie_opa2192.TSC

Kai

0 Tamara M Alani over 4 years ago

TI__Genius 10850 points

Hi Chao,

Thanks for your post. Please let us know if Kai's explanation is sufficient.

0 Michael Steffes over 4 years ago in reply to kai klaas69

Guru 48395 points

However Kai, op amp ATE almost always uses the servo amp technique - it also needs to measure Aol, CMRR, and PSRR - all very small,

0 Michael Steffes over 4 years ago

Guru 48395 points

Well Eddie, let me see if I can rephrase your question -

Apparently, you have a customer that feels like they need to replicate the typical outgoing ATE measurements for 1st the ADA4077 and then the OPA2192 as a possibly replacement in their end system.

The standard servo loop approach used by all op amp manufacturers does indeed have stability issues as it is switched between the different settings to measure the key DC parametrics.

A normal test engineer activity is to stabilize these with snubber networks - these are series RC loads that act to bandlimit the LG for the servo loop and increase phase margin

To realistically evaluate the possible oscillation they are seeing, the TI team would need the exact summing amplifier and test conditions to emulate the bench analysis usually done to set the snubber in simulation. It is unlikely they can go further without more circuit details.

0 Raymond Zhang1 over 4 years ago

TI__Guru* 76601 points

Hi Eddie,

I am going to close this inquiry, since the issues have been resolved over the internal email on 12/28/20.

If you have additional questions, please let us know.

Best,

Raymond

0 kai klaas69 over 4 years ago in reply to Raymond Zhang1

Guru 140200 points

Hi Raymond,

can you give some details on how the issue has been resolved? I'm very curious :-)

Kai

0 Raymond Zhang1 over 4 years ago in reply to kai klaas69

TI__Guru* 76601 points

Hi Kai,

We implemented Type II compensation method shown in figure 3 in the following article. Ccomp value is suggested to be approx. 30pf with approx. 80 degree phase margin.

The "two op-amp servo loop" circuit is mostly used in ATE tester. The customer does not want to change the two op-amp configuration, which the same circuit is used to screen other features in op amps.

https://www.edn.com/the-basics-of-testing-op-amps-part-4testing-op-amps-requires-stable-test-loops/

Best,

Raymond

0 kai klaas69 over 4 years ago in reply to Raymond Zhang1

Guru 140200 points

Thank you :-)

Kai

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OPA2192: OPA2192 to replace ADA4077 have testing issue