ADS7828: ADS7828

Hello,

Can you help clarify the issue? What do you mean by the ADC reading locking up?

Is the ambient temperature around the ADC itself -40°C, or is that the reading of the LM60?

How frequently does this issue occur? Have you only observed one device, or multiple with this same issue?

Regards,
Joel

Please refer to the attached 'Test setup diagram & Description' document.

Test setup Diagram & Description.pdf

Hello,

Thank you for helping to provide more information. I think the issue seems clearer now.

To confirm the issue outside of the reading from the GUI, are you able to take logic captures of the I2C lines during a normal conversion, and while the failure is happening?

As I understand it, you have only seen this happen occasionally on 1 to 3 devices. Are there any conditions you have observed that might cause this? Does the issue happen on the same devices, or does it happen at random on different devices?

Regards,
Joel

Dear Joel Meraz.

- As it is practically difficult to capture the I²C lines, we are instead providing the measured waveforms of the LM60CIM output, ADS7828 Vdd, and analog

  input pin during the abnormal temperature indication.

  We would appreciate it if you could review the attached waveforms and questions and provide your response.

- The issue is not limited to specific devices and occurs randomly on other devices as well.

Voltage waveforms measurement under abnormal temperature indications.pdf

Hello,

Firstly, thank you for the clear document presenting the schematic, issue, and tests you have performed thus far. It is very helpful. 

Seeing that the analog input is applied before the ADS7828 Vdd, that condition might be causing damage to the device. This condition should be prevented and avoided. See the E2E thread linked below.

https://e2e.ti.com/support/data-converters-group/data-converters/f/data-converters-forum/1346907/ads7828-the-max-voltage-range-for-the-analog-input-channels?tisearch=e2e-sitesearch&keymatch=ads7828%252520analog%252520input#

It seems like the spikes in the analog input pin waveform would be due to the charge kickback as a result of the sampling switch opening and closing during operation. The sampling capacitor charges and discharges periodically during the operation of the ADC, and what you are reading is this voltage. After conversion, the voltage on the sampling capacitor is reset. Can you further clarify what is the plot in yellow, and what is the plot in blue? Does this same signature appear during normal operation?

The reasoning for me wanting to see the I2C lines is to determine if the digital output is sent correctly, and if it may be an issue on the firmware/software side. Also to validate signal integrity and timing. 

How frequently does this issue actually occur across the 128 devices, and given a device that does fail, how often does it fail? I think that is still a little bit unclear.

Regards,
Joel