STM32G474VET6 ADC2_IN5 PC4 impendence issue

[Spam4tea]

Problem with input impendence on ADC2_IN5 / PC4 / pin 30 (100pin)

I have a high speed buffer video signal from a CCD device for high speed conversion - 5 signals going to ADC1,2,3,4,5

(Our first prototype based on STM32G474RET6 used ADC1->4 - no problems with a smaller part )

 

Upgraded to a 100 pin part - connecting the signal to ADC2_IN5 now overloads the video signal and pulls it down - same signal behaves properly when routed to ADC1,3,4,5. No pin stacking, no input multiplexing - always converting on the same channel:

VIDEO1 - ADC3_IN3 - PE13 p44 WORKS

VIDEO2 - ADC5_IN2 - PA9 p70 WORKS

VIDEO3 – ADC4_IN4 - PB14 p53 WORKS

VIDEO4 – ADC1_IN1 - PA0 p20 WORKS

VIDEO5 – ADC2_IN5 – PC4 p30 - PROBLEMS

 

Signal is driver with a high speed op-amp with 50 ohm matching.

DC part of the signal attenuated as well as the AC part.

[mƎALLEm]

Hello,

You need to give more details about the issue. 

How to write your question to maximize your chances to find a solution

Your schematics + probing each of ADC input screenshots + found results vs expected results

VIDEO5 – ADC2_IN5 – PC4 p30 - PROBLEMS

→ You need to be factual and describe the problem and its symptoms. 

[Spam4tea]

See images - I have also tried driving the signal harder by passing R20 - no real improvement

[mƎALLEm]

Thank you for updating your post by adding the screenshots.

But the legend is missing in the screenshots. Need to highlight the problem and describe it in details.

What is the part number used for U10?

[Andrew Neil]

input impendence (sic?) on ADC2_IN5

You mean impedance ?