TMS320F28235-Q1: ADC internal reference

Some other doubt:

1) If internal reference is used, 2.2uF capacitor should be used. If a cap with lower value, like 1uF, what happend?

2) How is ADCREFP and ADCREFM generated?

Thanks a lot.

Br, Jordan

Hi Jordan,

Please allow me a day to discuss this with some coworkers. Did this only happen once, since you said it is not possible to reproduce? Also, I would not expect anything like this to happen from using a capacitor value of 1uF, since this is just a bypass capacitor for filtering noise on ADCREFP and ADCREFM. I would only expect a change in the noise on the pin. 

Best Regards,

Ben Collier

Hi Jordan,

I have a few more questions about this design. How long has this design been in production? Or is it yet to go into production? In how many boards is this problem seen? In a board where the problem is seen, is the problem intermittent or permanent? If the problem is intermittent, how often is it seen? Was it just seen once? 

Also are you able to send me the schematic for this design in a private message? I have sent you a friend request on E2E. If you are not able to send me the complete schematic, it would be good to see the connections to the F28235 device, especially the connections on the analog pins.

Best Regards,

Ben Collier

Collier,

This is a product, already MP for more than 3 years. And this issue never happened before.

It's not possible to reproduce, even change the supply power from 3.15v to 3.6V. 

ADC sch, I'll send you soon.

Thanks a lot.

Br, Jordan

Collier,

After discuss with customer, they can't provide the sch, except these:

1) ADDLO to GND, whitch is connected VSS directly;

2) ADCRESEXT, 22.1K to VSS

3) VDDREFP/VDDREFM 2.2uF to VSS.

4) All of the ADC input signal less than 3V.

Br, Jordan

Hi Jordan,

Thank you for your responses. I will look into this, and I will try to get back to you before our planned call for next week.

Best Regards,

Ben Collier

Hi,

Any feedback?

Br, Jordan

Hi Jordan,

I think this issue would be better supported offline. I will email you with a status update.

Best Regards,

Ben Collier