THS4532: Can you help confirm the circuit design?

Hello Bo-Wei,

The design looks good overall; I did want to ask about the load on the outputs: were you able to consider the ADC input structure when you selected the output loading for the FDA?  I can review what I can find on the TMS320F28388 datasheet, I may have some recommendations.

The input RG resistors are quite larger (I understand why, you need attenuation).  This may present a larger input offset current: do you know if your design requirements are sensitive to voltage and current offset?

I can spend some more time reviewing the ADC and how to best pair this FDA to the converter.

Please send any updates as you have them.

Best,

Alec

hi

We have not considered the impact of RG. Maybe we have neglected it. I would like to ask you to explain to me the impact of RG. What is your suggestion?

Any updates?
It can help us learn from your thoughts.

HI Alec

Got it. Thank you for your guidance. This is something we should pay attention to when doing OPA-related designs in the future. It is a very valuable lesson!

But my colleague has some issues when using the same OPA. I hope you can help. The following is his design. The expected Gain value is 5.1, but it is always around 4.59.

 

Hello Bo-Wei,

Please allow me time this week to check on this; overall I do not see any issues with your colleague's schematic.

Best,

Alec

Hello Bo-Wei,

Please allow me time this week to check on this; overall I do not see any issues with your colleague's schematic.

Best,

Alec

We will continue to test whether the accuracy of R or C causes any problems.
We have done some experiments.

1. Remove the OPA backend load. But the result is still the same
2. Disconnect the power supply of OCM. But the result is still the same

TKS.

Hello Bo-Wei,

Thank you for sharing your debugging steps and results.

I can provide an update by the end of this week, but likely sooner.

Best,

Alec

HI Alec

Thank you for your positive response!

We really don't have any ideas at the moment, and we look forward to your confirmation.

Hello Bo-Wei,

I am working on a solution for you.

Does the gain accuracy to the expected value improve if the VREF voltage is changed to mid-supply (1.65V)?

Could you also share if there is a load on the outputs of the fully-differential amplifier?  From the shared circuit I only see the net names & feedback loop.

Best,

Alec

HI Alec

Thank you for your suggestion.we will try to adjust the voltage

I will provide you with some of my backend load.After we output from opa, we will go to two places

1. TMS320F28388D ADC
2. After passing through TLV3202AIDR, convert the sine wave into a square wave and then enter the EQEP function pin of TMS320F28388D


TKS.

HI Alec

Sorry, I'll add that a more complete attachment should be as follows, and it also includes a MAX1198ATE ADC

Hello Bo-Wei,

Thank you for providing the updated and full circuit schematic.  I am following up on some thoughts I have about the circuit design tomorrow, so I can provide a response.

Thank you for communicating and sharing the details.

Best,

Alec

HI Alec

Do you have any ideas or updates?

Hello Bo-Wei,

I was unable to look into more details last week; I do have time tomorrow to review this for you.

Thank you.

Best,

Alec

Thanks，

Any updates?

Thanks，

Any updates?

Any updates?

Hello Bo-Wei,

Can you try changing the passive components which connect the output of the THS4532 to the internal ADC of the TMS320F28388?

I am concerned about this 100 Ohm impedance compared to the much higher impedance seen at the TLV3202 inputs.

This could affect gain performance.

Best,

Alec