DAC80502: the overshoot at DAC output happen when the output setting change from 0V to 2.5V.

Hello Akihisa-san, 

Can you share more details about the output load? I see some resistors in the schematic but I'm not sure what the other blocks are. 

Is there something that changed between the first prototype and this one? Is it possible to do an A-B-A swap between a known bad device/board and a good device/board to see if the issue follows the device or the board? 

How many units were tested in the prototypes, and how many units are seeing the issue?

It's possible that the devices seeing the issue have a negative offset and are seeing excess overshoot due to the op amp needing to drive out of the negative rail (ground), but I am a bit surprised by the magnitude of the overshoot..  

Best,

Katlynne Jones

Katlynne-san,

Thank you for your reply.

Katlynne Jones said:

Can you share more details about the output load? I see some resistors in the schematic but I'm not sure what the other blocks are. 

The customer observe VOUTB waveform as the following circuit. there are 2 resisters as the load, but there are no load when the customer checked the waveform of VOUTB.
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The customer mentioned that they have confirmed that the 110 Ω and 150 k Ω loads are operating normally.

Katlynne Jones said:

Is there something that changed between the first prototype and this one? Is it possible to do an A-B-A swap between a known bad device/board and a good device/board to see if the issue follows the device or the board? 

The customer checked 5 boards. Then they found this phenomenon in the only one board.
They think that  it is highly likely that the reproduction will not be possible if the swap is carried out.
As mentioned below, even though it goes down to 5V at 0V → 2.5V, it does not happen at 0.001V → 2.5V.
Therefore, they believe that the possibility of the impact of the VOUTB connection load is low.


They have one more question. Would you please confirm if there is anything you can think of in the settings for the IC?  If you think that this IC is abnormal one, please let me know.

Your advice is appreciated.

Best Regards,
Akihisa Tamazaki

Hello Akihisa-san, 

It sounds like the device could be damaged then. An A-B-A swap would confirm this and also rule out any potential issues due to bad soldering. If the customer would move forward with a quality return (assuming the device is from an authorized distributor), then we would request them to try the A-B-A swap before shipping us the sample. 

It is typical for a DAC output to see larger overshoot when driving out of the negative (or positive) rail which could explain why the issue is not seen when driving from slightly above the rail, but the magnitude of the overshoot in the customer's scope plot is much more than expected. 

There are no register settings that would cause this type of behavior. 

Best,

Katlynne Jones

Katlynne-san,

Thank you very much for your comment.
The customer also think that this device have damaged.

Katlynne Jones said:

It is typical for a DAC output to see larger overshoot when driving out of the negative (or positive) rail which could explain why the issue is not seen when driving from slightly above the rail, but the magnitude of the overshoot in the customer's scope plot is much more than expected. 

The customer seems to not to a little believe your comment. Because when changing from 0.01V to 2.5V, there will be no overshoot, but when changing from 0V to 2.5V, there will be a large overshoot. Customer wants to know if it is better to think that the buffer part of the DAC output has been damaged than the control part of DAC. so would you please advise us if it is a possibility where in the DAC may have damaged. 

Your help is appreciated.

Best Regards,
Akihisa Tamazaki

Katlynne-san,

Thank you for your comment.
I will discuss with the customer again, then I will ask  you again.

Best Regards,
Akihisa Tamazaki