[FAQ] ADS129x: How do I verify that my ADS129x device is still functional?

When most ADCs appear unresponsive, a few basic debugging techniques can help verify whether or not the device is still functional. Below are some basic steps to take when an ADS129x device appears unresponsive:

1. Apply power to the device. Then probe the device supply pins or nearest decoupling capacitors to verify that analog and digital supplies are reaching the part as intended.
2. Probe any internal voltage pins or their respective decoupling capacitors. These voltages may include the internal reference and multiple VCAPx supplies. The internal VCAPx supplies vary from one ADS129x device to another. Check as many internal voltage nodes as you have available on your device.
   1. VREF = VREFP – VREFN (Note: internal reference buffer must be enabled)
   2. VCAP1 = AVSS + 1.2 V
   3. VCAP2 = (AVDD + AVSS) / 2
   4. VCAP3 = AVDD + 1.9 V
   5. VCAP4 = AVSS + (VREFP + VREFN) / 2

   For ADS1x91/2,

   1. VCAP1 = AVSS + 1.2 V
   2. VCAP2 = AVDD +1.9 V
3. Enable the internal master clock or provide an external master clock per the data sheet specifications.
4. Pull the START pin high or send the START SPI command.
5. Probe the /DRDY pin with an oscilloscope. If the device is converting, you will observe pulses on the /DRDY pin with a period between falling edges equal to the device’s default data rate. ___|___|___|___ ...+
6. As noted in Figure 93. Initial Flow at Power Up in the datasheet, the /RESET pulse after tPOR is essential for bringing up the digital core in the correct state.
7. Send the SDATAC command to exit Read-Data Continuous (RDATAC) mode.
8. Read the ID register. Confirm that the device ID corresponds to the correct device and channel count. If the ID register does not read back correctly, most likely there is an issue with the power-up timing.
9. Attempt to write registers and correctly read them back.
10. Attempt to read data from a known input signal to confirm correct communication and code to voltage conversion.

If you are unable to compete all of the steps above, try resetting the device while the analog and digital supplies remain present. Make sure that the power supplies have had sufficient time to power up and the Power-On Reset (POR) timing has be followed (section 11.1 Power-Up Sequencing in datasheet) before attempting to communicate with the device. For more information, check the device data sheet for an example Initial Power-Up Sequence routine and Power-On-Reset (POR) timing.

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This post applies to ADS1191, ADS1192, ADS1291, ADS1292, ADS1292R, ADS1294, ADS1294R, ADS1296, ADS1296R, ADS1298,   ADS1298R, ADS1299-4, ADS1299-6, and ADS1299.