This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

  • TI Thinks Resolved

ADS1248: ADS1248 system monitor

Part Number: ADS1248

Hi,

In my project I have two ADS1248, one adc gives me linear output but other not. I used system monitor control feature to check problem on AVDD, DVDD, REF.

There seems to be difference in offset calibration reading that is (AVDD + AVSS) / 2.

For ADC which works fine I got readings like :

0000000081
0000000034
0000000118
0000000012
0000000050
0000000155
0000000127
0000000181
0000000052
0000000025
0000000061
0000000108
0000000103
0000000030
0000000087

For ADC which fails to give linear output readings are like :

0000065641
0000000000
0000065577
0000065589
0000065595
0000065557
0000065577
0000065641
0000065623
0000065585
0000065559
0000065577
0000000028
0000000018
0000065619
0000065547
0000000002

AVDD : 2.5V

AVSS: -2.5V

DVDD: 3.3V

REF : Internal 2.048V

If there is problem in mid supply (i.e (AVDD + AVSS) / 2) so whether it is AVDD or AVSS or GND?

what does this variation in count signifies?

  • Ritesh,


    If you have both inputs set to (AVDD+AVSS)/2, the input should be close to 0V. Normally, this is where you would want to run the offset calibration. For the ADS1248, a SELFOCAL would set this automatically. If you want, you could read the offset and gain calibrations just to check that these values are properly set.

    Looking at the good data, your values are just on the positive side. In the bad data, the numbers are close to 0, or they are close to 65000. My guess is that the problem is in how you process the data. The bad values are close to FFFFh (65535) and I think that this is a problem in how your code processes negative numbers. Go through your code, but I think the code conversion is off. Normally a -1 would be FFFFFFh, not FFFFh.

    Check the code, but if you don't see anything, I would definitely get a scope shot of the SPI communications when the data read is bad. If you have a logic analyzer, that would be better to get all SPI lines + DRDY.


    Joseph Wu
  • In reply to Joseph Wu:

    Ritesh


    I haven't heard back on this question for a while. Were you able to solve your problem? As I mentioned in my previous post, I thought this might be some code conversion issue, but it would still require some testing to prove that out.

    I'll close this post for now, but if you continue to have problems, post back and we can continue to work on this. If you do post back, let me know what you've tested so we can discuss it.


    Joseph Wu
  • In reply to Joseph Wu:

    Hi Joseph,

    Thanks for your reply, problem was in data read on spi, I was not able to read bit 16 that is why it was showing non linearity.

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.