ADS131E08EVM-PDK: Weird ADC Output

Hi Richard,

I've asked Naser to ask you to try running the internal test signal of the ADS131E08. Can you do that and then post the result?

Hi Tom,

Thanks for the quick response.

I set "TEST Source" for "Generated Internally" on ADC Register page as well as Channel One Input to "Test Signal" then I got:

Did I set the test signal correctly?

Thanks,

Richard

Hi Richard,

You need a larger sample set, change samples/Ch to at least 8000. You should get something that looks like Figure 16 in the ADS131E08EVM-PDK Users Guide.

Hi Tom,

I changed the sample to 10k and here it is. I didn't see the correct testing signal. 

Thanks,

Richard

Hi Tom,

Here is another one with 50k samples. And I got the correct testing signal. so what could be wrong with my previous testing?

Thanks,

Richard

Thanks Richard,

Something is wrong then, please review the ADS131E08EVM-PDK Users Guide and be sure all the jumpers are correctly set and that you have the proper voltages applied to the MMB0. If everything checks out properly, we can talk about getting you a replacement setup.

Sorry Richard,

I think we crossed paths in the clouds somewhere. The last post looks correct. Check your signal generator output directly on a o'scope and make sure it's output is correct.

Hi Tom,

I just started my evaluation yesterday and everything should be default setting. I confirmed the jumpers by following the user guide and all looks good to me. Can you please advise what I should do next?

Thanks,
Richard

Hi Tom,

Yes, I did check the signal generator on my scope and the output signal was correct, 0.5Vpp, 500Hz continuous sine wave.

Anything else I need to check?

Thanks,
Richard

What about grounding? Can you tell me how you are referencing the signal generator back to the ADS131E08EVM-PDK?

Hi Tom,

The signal generator was powered by a AC/DC adapter and I connected the Ch1 output directly to Ch1 of the ADC.

Thanks,
Richard

Hi Tom,

By default, the EVM shipped with AVDD = 2.5V and AVSS = -2.5V. The result was in my first post. Then I set JP1 so AVDD = 3V and set JP7 so AVSS = 0V. I got the exactly same result. The output of the ADC swung between +/-0.25V for both cases.

On the other hand, U5 on MMB0 board was extremely hot.

Thanks,
Richard

Hi Richard,

What sort of power supply are you using for the MMB0? If you've gone from bipolar +/-2.5V supply on the ADS131E08 to unipolar 0-3V, you need to be sure you are not driving the inputs below ground.

Hi Tom,

I used 12V AC/DC adapter to power MMB0. U5 is always hot no matter the signal generator is connected or not.

I used one 1.5V battery instead of the signal generator and here is what I got. 

Thanks,

Richard

Hi Tom,

From the last result, I really think something is wrong with the EVM.

Is there anything else you would like me to try?

Thanks,
Richard

Hi Richard,

I don't have the Users Guide in front of me at the moment, but when we did ship out power supplies with these boards, we provided a 6V DC wall adapter (center positive) AD/DC source. If the U5 voltage regulator on the MMB0 is getting 'extremely hot' (over 60`C you can't keep your finger on it) then it's dropping too much power. U5 is a 5V regulator so with a 12V source, you should be dropping 7V at a few hundred mill-amp MAX, so that could be a few watts. If the regulator is dropping out due to thermal overload, that might be the problem. Do you have a 5V bench supply to provide an alternate power source for the MMB0?

Hi Tom,

The EVM I received did not include any adapter.

On the page 5 of the user guide, it states the supply to MMB0 board should be 5.5VDC to 15VDC. That is the reason I used 12VDC.

U5 was extremely hot and I cannot put my finger on it for 2 seconds.

I don't have a 6V adapter but I will try to use a bench power supply to power up the MMB0 board tomorrow and will let you know the result.

Thanks,
Richard

Hi Tom,

I got similar result with 5V supply to MMB0 board.

Thanks,

Richard

Hi Richard,

If it's OK with you, I'll contact you though your My.TI e-mail account and try to arrange getting you replacement hardware.

Hi Tom,

Yes, please contact me though myTI email.

Thanks,
Richard