ADS7808: Cold temperature failures below -20C

Hello Richard,

No known cold temperature problems with the ADS7808.  I am not aware of any changes to the device after 2009.

The ADS8508 is the newer generation device, and is pin-to-pin drop-in, although there are some differences that may require timing changes to the software.  Application note Upgrading From ADS7808/09 to ADS8508/09 Devices details these differences.

Typically when parts fail at cold temperature extremes for some lots, and no issues with other lot material, it is usually a timing issue.  We have wide margins for setup and hold times to accommodate the full temperature range, as well as lot to lot and part to part variations.  Many times, if a timing spec has been accidentally exceeded, the device will perform fine and the problem will not show up until a different lot of material at cold temperature.

Can you provide some additional details about the design?

Mode of operation:

1. Internal or external clock?

2. Tag mode (daisy-chain of multiple ADCs)?

Can you capture the following waveforms with a scope or logic analyzer over a full data transfer frame? DATACLK, DATA, R/C-CS, BUSY.

Regards,
Keith Nicholas
Precision ADC Applications

Hello Richard,

The ADS7808 changed fab sites in 2009.  It is likely that there is a shift in the typical value for the timing specs, but still within the min/max specified in the datasheet.

Based on your description, I think a timing spec violation is the most likely cause, although it could be something unrelated.  If you would like to share a picture of the SPI waveforms over a full frame, I will take a close look to see if anything looks out of spec.

Regards,
Keith