DAC9881: DAC Output is not consistent

Jaimanoj Jayaraman

Intellectual 570 points

Part Number: DAC9881

Hi TI team,

We are using DAC9881 for generation voltage as per the requirement .

Generate below voltages by setting DAC count 1 time

1. Generated Voltage 1 using DAC - 2.270 approximately

2. Generated Voltage 2 using DAC - 0.317 approximately

DAC9881_SIGNAL_CAPTURE.zip

Issue Observed:

The DAC output is not consistent. If set the DAC count sometimes i get the expected voltage but sometime i observed lesser voltages.

I attached SPI signal for your reference. To analyze the Data , kindly install the below software from the link

https://www.saleae.com/downloads/

Our Analysis:

If we set the DAC multiple times(10 Times with some delay) frequency of occurence of issue reduces. Means output of DAC is almost expected. Very few times it deviates[Lesser voltage]. But it is not good to set DAC multiple times.

Our expectation --> If we set the DAC one time also, it should provide correct voltage as per the count woithout any deviation

Kindly advice in this situation with high priority.

Thanks and Regards

Manoj

over 5 years ago

0 Uttam Sahu over 5 years ago

TI__Genius 14220 points

Hi Jaimanoj,

Thank you for your query. I will get back by Monday.

Regards,
Uttam Sahu
Applications Engineer, Precision DACs

0 Uttam Sahu over 5 years ago in reply to Uttam Sahu

TI__Genius 14220 points

Hi Manoj,

I couldn't go through all the datasets you had provided. Looked at few of them and them seem ok. The only suspect I have is the USB/BTC pin. Could you please check whether it is floating or toggling?

Regards,
Uttam

0 Jaimanoj Jayaraman over 5 years ago in reply to Uttam Sahu

Intellectual 570 points

Hi Uttam,

Please see our circuit attached. In our case it is not toggling or floating, It is always high.

You mention the captured data seems to be ok but we observed some issue in shared SPI signal captured

Issue Observed:

We are setting the DAC register. correct behavious is when we set DAC value in register, we get return value which is same as value set in register.

But in some captured SPI signal we are not getting correct return DAC value. Means It is not same as what we set

Thanks and Regards

Manoj

0 Paul_Frost over 5 years ago in reply to Jaimanoj Jayaraman

TI__Guru 52683 points

Hi Manoj,

I does not appear the image was attached.

Thanks!
Paul

0 Paul_Frost over 5 years ago in reply to Paul_Frost

TI__Guru 52683 points

Hi Manoj,

What SPI speed are you operating at? Have you verified that your timings are compliant with figure 1?

Generally when issues like this happen it is due to insufficient edge timing or the wrong phase and polarity being used by the SPI Master. In addition an oscilloscope may show if there is significant digital crosstalk from some other source.

Thanks!
Paul

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DAC9881: DAC Output is not consistent