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AD5781 glitch impulse

Category: Hardware
Product Number: AD5781

Hi!

A few questions about the glitch impulse and update of the DAC.

In the datasheet (https://www.analog.com/media/en/technical-documentation/data-sheets/AD5781.pdf) in figure 43-45 the glitch impulses are shown when an RC low-pass filter is used. However, the value or R and C is not given as I can see.

What is the R and C values on the filter?

In figure 45, Cx referees to what capacitor? Where is it located?

In figure 48, where should the output clamp be located and look like?

In our application LDACn is hardwired low and the SPI interface is used to load/output values. In the case the same data is written to the DAC, will the DAC still update the registers and generate the glitch impulse, or only when the data is new from previous state?

Best regards

Joakim

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  • Hi Joakim, 

    The R and C values are given on note 6 under table 3. R=300 ohm and C=143 pF (total cap seen by the buffer, includes lead capacitance etc). 

    The Cx on Figure 45 is added cap load onto the 143 pF inherent one. 

    The output clamp is an internal feature of the AD5781, set by the OPGND bit on the Control Register. This feature is also enabled during POR. Essentially, figure 48 is the effect (to the output) of disabling the output clamp feature.

    Sending the same code will not update the registers and there should be no glitch due to writing the same code. 

    Regards,

    -ian

Reply
  • Hi Joakim, 

    The R and C values are given on note 6 under table 3. R=300 ohm and C=143 pF (total cap seen by the buffer, includes lead capacitance etc). 

    The Cx on Figure 45 is added cap load onto the 143 pF inherent one. 

    The output clamp is an internal feature of the AD5781, set by the OPGND bit on the Control Register. This feature is also enabled during POR. Essentially, figure 48 is the effect (to the output) of disabling the output clamp feature.

    Sending the same code will not update the registers and there should be no glitch due to writing the same code. 

    Regards,

    -ian

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