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AD5666 bad output voltage

Question asked by ObrechtCh on Sep 3, 2015
Latest reply on Oct 6, 2015 by KenK

I use the AD5666 quad 16bit DAC in my application.

During my calibration routine (to calculate gain and offset error from the circuit) I see curios output voltage.

 

output_voltage.PNG

You see a extract from the calibration solution graph.

X-axis is the set value in Digits and the Y-axis is Output-Voltage in Volt

The incrementing is slowly (>500ms) but the SPI communication is fast.

I've a FPGA for serve all SPI components. The FPGA write every 20µs all channels.

See scope

tek00019.png

The purple signal is the DAC-chip-select

(SPI Clock is 13.5MHz)

The sequence is Ch1 -> Ch2 -> Ch3 -> Ch4 -> Ch1 -> Ch2 -> ...

I write direct the channel with command 0x03 (write and update DAC Channel n)

The Pin LDAC is fix connected with ground.

 

Everybody have a idea, why I have this output characteristic?

I can manipulate this behavior with the update speed but not with the SPI clock speed.


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