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DAC60508: Too high noise on DAC outputs of DAC60508

user5376422
Prodigy 10 points
Part Number: DAC60508

Hello everyone,

We had some noise on the DAC outputs of DAC60508. 

We are using  this chip with compatible QFN to dip adapter. The CS pin of the chip is pulled up with 10k resistor. Also, a 100pf capacitor is added between CS and ground. The SPI master (STM  Nucleo F746zg) sends 0xCCC0 (approximately 4V) to the DAC2 register. The yellow signal is representing the DAC2 output in the figure. But there is noise on the DAC2 output when the SPI clock (green signal) active. According to the Figure 48 on the datasheet these noise is approximately 1mV. 

Could you have any explanation why the noise level is too high?

The chip configuration registers are settled as follow:

SYNC : 0x0000

CONFIG : 0x0000

GAIN : 0x00FF

  • 0
    TI__Guru 52663 points

    Hi, and welcome to the e2e forum.

    You are seeing digital feedthrough, but it is likely from your board or ground plain.  The problem with dip-adapter boards is that you have long inductive paths in your digital communication that can couple to the other signals.  It is possible that you are not really seeing this high noise on the output, but rather the ground signal that you are connecting the oscilloscope to as well.  I recommend a few things:

    1.  Slow down your digital communication.  You are using an SPI clock of about 5MHz in this configuration.  If it is not necessary, you can reduce that speed.

    2. You could slow down the edges by adding a small cap in parallel and a small resistor in series.

    3. You can improve your ground and power connections.

    Let me know if any of those options help.

    Thanks!

    Paul