DAC108S085: Output random value

Part Number: DAC108S085

Hi,

i've the following issue, the output is not able to execute commands, the output value is random. i attach the SPI image.

Yellow trace is CLK, Cyan trace is Din, Magenta trace is SYNC anf the Green trace is the output of zero channel, the programmaed value is 0x1ff = 6V. If i use the 0xA00F command the output value run in random mode. I haven't any idea about this issue.

The dac init sequence is the following: Broadcast command to zero, Mode to 100k for the channels 4, 5, 6, 7 and WTM mode enabled. Thanks in advance for your support.

Francesco

over 1 year ago

0 Lucas Burnette over 1 year ago

TI__Expert 4590 points

Hi Francesco,

We are reviewing this and will get back to you soon.

Thanks,
Lucas

0 Paul_Frost over 1 year ago in reply to Lucas Burnette

TI__Guru 53773 points

Hi Francesco, can you share your schematic here?

0 FV over 1 year ago in reply to Paul_Frost

Prodigy 20 points

0 Paul_Frost over 1 year ago in reply to FV

TI__Guru 53773 points

It looks like you have some pretty high gain in the schematic (5x)? It is hard to read.

Can you try measuring a few different DAC outputs before and after the output buffer? For example, set the DAC to 1/16th scale, and confirm the output, then 1/4th scale, then 1/2 scale. Is the output really "random", or is there a pattern?

0 FV over 1 year ago in reply to Paul_Frost

Prodigy 20 points

4812.DAC.pdf

Hi Paul,

thank you for your support, the output of teh dac before and after the output amplifier U35 are coherent with the device; my issue is the not controlled output of the dac in function of the data sended via SPI; the output appear "random" because seems that the phenomena caused by a "shifting" of the data from the internal registers of the DAC. My command send data to only one channel for test the firmware routine.

See you soon.

0 Lucas Burnette over 1 year ago in reply to FV

TI__Expert 4590 points

Hi Francesco,

I apologize for the delay.

Can you detail each of your initialization and writing steps? (I'm looking for the hex values specifically to go through them)

If you also have a logic analyzer, you can verify it is being sent correctly.

Thanks,
Lucas

Data converters

Data converters forum

DAC108S085: Output random value