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AMC7836: DAC timing for clear and re-enabling

Lucas Pucheta
Intellectual 2468 points
Part Number: AMC7836
Other Parts Discussed in Thread: AMC7904, AFE10004

We are investigating a method of fast turn on and fast turn off the high power LDMOS transistors on the radio and I would like to know some information about the timing of the DAC Clear Alarm feature (7.3.1.3 below) of the chip. Specifically, I would like to know the timing of the DAC clear (switching to zero code) and DAC re-enabling (time to restore DAC output to previous value). I would like to know the timing relative to the ALARMIN GPIO trigger. Do you know of a document that has this information?

 

All I could find in the DS was a output voltage settling time of 10uS but when we tested this feature it was several hundred milliseconds we seen.

  • 0
    TI__Guru 52683 points

    Hi Lucas,

    You might see hundreds of microseconds if there is a capacitive load on the DAC output.  Is there?

    The delay from CLEAR or the alarm status getting removed to the DAC starting to update should only be a microsecond or two (assuming no cap load).  Then we should see normal slewing and settle in some time around the ~10 to 15µs.  If there is a cap load, then you cannot expect fast settling.  In most cases, if a customer want to implement fast switching, we recommend a device like the AMC7904 or AFE10004.  Email me if you would like more detail on the AMC7904. 

    Otherwise, the customer can use an external SPDT analog switch to toggle between a steady Vgs-on voltage and ground.

    Thanks,

    Paul