• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 47 subscribers
  • Views 959 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

Original question:

ADS1299: ADS1299 VCAP1 appear -1.1V , SPI doesn't work

ADS1299: VCAP values

John N
Prodigy 20 points

Part Number: ADS1299

Tool/software:

Hello, I am doing board bring up for the above design and have noticed that the VCAP values are off. In addition I am having trouble communicating with the device. These are the measurements I have taken:

VCAP1 = 1.2V

VCAP2 = 2.5V

VCAP3 = 6.8V

VCAP4 = 0.3V

VREFP = 0.2V

VREFN = -2.5V

AVDD = 2.5V

AVSS = -2.5V

DVDD = 3.3V

If someone can verify my design and check if these voltage values normal that would be great.

Thank you!

  • 0
    TI__Guru 68676 points

    Hello John,

    Thank you for your post.

    Some of these voltages appear to be measured with respect to GND, others with respect to AVSS. Can you confirm?

    We have listed some FAQ topics on our E2E BIOFAQ page, which cover the expected VCAPx voltages and basic initialization debug. Please take a look and let me know if this helps.

  • 0 in reply to Ryan Andrews
    Prodigy 20 points

    Hi Ryan, 

    VCAP1, VCAP2, VCAP3, VCAP4, VREFP, and VREFN are all referenced to AVSS. AVDD, AVSS, and DVDD are referenced to ground. I did take a look at the E2E BIOFAQ page, and it looks like VCAP1, VCAP2, and VCAP3 are correct. However, there could potentially be an issue with VCAP4 or the internal buffer that feeds VREFP and VREFN pins. 

    Also, I tried to just get the device ID, but am reading 0. Any thoughts on this?

    Thanks,

    Brandon

  • 0 in reply to John N
    TI__Guru 68676 points

    Hi John,

    Thanks for checking. 

    By default, the internal reference buffer is powered down. This would explain why VREFP and VCAP4 (VREF / 2) are not measuring correctly.

    Have you followed the initialization steps outlined in sections 10.1.1 and 11.1? After power up, it is important to follow the power-on reset steps in section 11.1 to ensure the device initializes in a known state. You should see /DRDY toggle at the default data rate to know that the device is operating as expected (assuming START = 1). Then, in order to read the Device ID register, you'll need to first send the SDATAC command to exit RDATAC mode.

    Regards,

    Ryan

  • +1 in reply to Ryan Andrews
    Prodigy 20 points

    Hi Ryan,

    Thanks for the information. After some more troubleshooting, we were able to communicate with the device and read values. It turned out to be an issue with our buffer size. Initially we had a buffer size of 3 bytes, when it should be 4 bytes. We are able to write and read registers now.

    uint8_t config1_command[4]; // config1 command

    HAL_SPI_Transmit(&hspi1, config1_command, 4, HAL_MAX_DELAY);

    Thanks,

    Brandon