DAC122S085: DAC Seems to be Resetting in Cold Temperatures

Jacob Hays

Part Number: DAC122S085

I have a design in which I use the DAC122S085 to set the current limit for a motor drive.

The design seemed to work great but I have been running into issues when testing at -40C. Basically, the DAC is commanded an output on boot up, thus setting the current limit. This current limit is set at boot up and never really touched again. What is odd is the DAC output drops to 0V after attempting the first move from a cold start. If I command the DAC with a new output value after it has an output of 0V it seems to maintain that output.

At first was thinking it may be a software error but no evidence of that. Then I thought the DAC may be rebooting if the 3.3V was drooping at all, but it appears to be rock solid.

I have attached a capture (albeit a bad noisy capture as my measurement setup is non-ideal), may try to make a better setup for tomorrow.

Thought I would post on here to see if there are any other ideas of what may be going wrong. I am hitting a wall in the debugging process. I am going to get better captures later today or tomorrow.

Yellow: 3.3V Rail (Across the DACs Capacitor)

Green: Chip Select Line

Blue: DAC Output

Pink: CLK

Thanks.

over 3 years ago

0 Jacob Hays over 3 years ago

Prodigy 30 points

Attached is a higher Res capture.

0 Akhilesh K over 3 years ago in reply to Jacob Hays

TI__Mastermind 19086 points

Hi,

what is the DAC output you are setting to at power up?

Did you monitor reference voltage also?

Please share schematics including output stage

Regards,

0 Jacob Hays over 3 years ago in reply to Akhilesh K

Prodigy 30 points

The DAC Output I am setting it to is shown in the second capture more clearly. Approximately 950mV, I have tried a handful of different values and they all have the same behavior after soaking for some time.

I did look at the reference voltage but do not have a capture as it was pretty solid at 2.5V, I had the thought that a droop in the reference could cause an issue but saw that when the output was 0V the reference voltage was at 2.5V still.

To elaborate after the above capture if I resend the command to set the DAC the DAC goes to the commanded output. If there was an issue with the reference voltage the output would still remain at 0V correct?

Here are the relevant snippets from schematics.

0 Jacob Hays over 3 years ago in reply to Jacob Hays

Prodigy 30 points

I have tried to replicate the motor stalling within our lab in ambient temperatures. The DAC operates fine in ambient temperature conditions, when trying to move the motor while its stalled the DAC output maintains its output in ambient conditions.

0 Akhilesh K over 3 years ago in reply to Jacob Hays

TI__Mastermind 19086 points

Hi,

Can you probe SPI signals at cold start and verify that frames are OK?

Regards,

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DAC122S085: DAC Seems to be Resetting in Cold Temperatures