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AD5421 current impulses on SPI writes


I cyclically write to Control register with values 0x75A0 or 0x74A0. Right after that I write a new DAC code. 

I alway see current impulse on the HCF_TOOL-31 output during "Noise during silence" test conditions (see picture below) right after SPI exchange to DAC finished.

If I switch off internal ADC (writing 0x7520 or 0x7420 to Control register), the first impulse doesn't appear. The second impulse

is always in place.  Have anyone faced this?

SCH added
[edited by: zhenyasun at 1:43 PM (GMT 0) on 8 Jul 2019]