AD5429: DAC not responding to sending of serial word

Document created by analog-archivist Employee on Feb 23, 2016
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Being about to evaluate a design with an AD5429, I have not succeded
establishing the SPI communication.

Detailed configuration:
  variable-gain amp
  SPI active SCK edge: H-to-L transition
  update mode: asynchronous
  Fsck<10MHz

Test failed:
  starting the frame with SYNC\ H-L
  transition
  sending the sequence 0x8000 for
  loading with zero
  frame end by SYNC\ L-H
  subsequent
  update with LDAC\ H-L transition.

No gain-changing reaction can be observed.

 

There are several possible reasons why you might not be seeing any reaction
from the AD5429.

Firstly, the DAC is loaded with zero scale when the part is powered on, so if
you again load zero into the DAC refgisters you will not see any changes. Try
loading with a different value to see if you get a reaction.

Digital Interface
Are the DAC and the ucontroller referenced to the same ground? (i.e. do the DAC
inputs see the same signal that the uC transmits?) Are the SCLK signals clean
and free of glitches?  Extra "clock pulses" due to noise can cause the SPI
interface to lose synchronisation.
Have you respected the 13ns timing between the SYNC H-L and the SCLK H-L?
Do you apply 16 full SCLK cycles to fill the input register?
Do you write (intentionally or by accident) to the control mode of the part -
Control bits = 1101

Analog problems
Is the output op amp powwered from a bipolar (+/-) supply?
Have you connected the DAC similar to figure 37 page 15 of the REVA datasheet?
Is an input signal present at Vref? (if not you won't see anything change when
you change the gain)

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