DAC108S085: Analog output value is 4 times the computed value.

stevenh

Guru 20045 points

Part Number: DAC108S085
Other Parts Discussed in Thread: TMS320F28379S,

Tool/software:

Hello,

The DAC108S085 in my design is interfaced to a SPI port on a TMS320F28379S. The SPI's clock polarity and phase is set to SPI_PROT_POL0PHA1.

I am noticing the Analog output value is 4 times the computed value.

What could be causing this issue? The issue also occurs for other clock polarity and phase settings.

Thanks,
Stephen

8 months ago

0 Katlynne Jones 8 months ago

TI__Mastermind 41513 points

Hi Stephen,

What value reference are you using? Can you monitor a SPI write on a scope and share a screenshot? Please share the code you are intending to write, and the resulting voltage output of that write.

Best,

Katlynne Jones

0 stevenh 8 months ago in reply to Katlynne Jones

Guru 20045 points

The reference is 5V. I will try to get some SPI screenshots.

Why are the last two bits shown as Xs in the image below.

+1 Katlynne Jones 8 months ago in reply to stevenh

TI__Mastermind 41513 points

Hi Stephen,

The data field is 12 bits wide so that the same software can support our 12-bit and 10-bit devices in this family. The last two bits in the 12-bit field are X because they are "do not care". Only the left most 10 bits are used.

Best,

Katlynne Jones

0 stevenh 8 months ago in reply to stevenh

Guru 20045 points

Ok, I misspoke earlier. I should have said "In order to get the correct analog output value, the digital input value needs to be multiplied by 4."

This matches what Table 2 is showing. Therefore, there aren't any issues.

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DAC108S085: Analog output value is 4 times the computed value.