DAC8560: Output going to 0V when sharing SPI lines

Andres

Part Number: DAC8560
Other Parts Discussed in Thread: ADC128S102,

I have a DAC8560 and ADC128S102 sharing SCLK and MOSI lines. I can set the DAC output but when I then poll the ADC the output goes to 0V even though the DAC8560 CS is held high.

I can't see why this is happening.

over 2 years ago

+1 Paul_Frost over 2 years ago

TI__Guru 53573 points

Hi Andres,

Is it possible that some other glitch is occurring on the VDD supply during this communication? Can you set up the scope to trigger on the VDAC output change and reduce the time scale to catch any other glitches that might be happen? I see some digital xtalk on the CS line, does that error get more extreme if you zoom in?

Thanks,

Paul

0 Andres over 2 years ago in reply to Paul_Frost

Prodigy 30 points

This has been resolved. There was a glitch on the DAC CS line that I had to filter out.

0 Andres over 2 years ago in reply to Paul_Frost

Prodigy 30 points

One question - why would the glitch on the DAC CS reset the output? Per the datasheet, my understanding is that a CS glitch like that would just be ignored.

0 Paul_Frost over 2 years ago in reply to Andres

TI__Guru 53573 points

I suppose it would depend on the magnitude and the duration of the glitch. Is it possible the line was held below the VIH level during the entire write? Could there be significant ringing on the clock or data line during the event as well?

0 Andres over 2 years ago in reply to Paul_Frost

Prodigy 30 points

I measured the glitch on the DAC CS pin to be <20ns. I will inspect for ringing on the other lines - though initial probing didn't show anything significant.

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DAC8560: Output going to 0V when sharing SPI lines