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Original question:

AMC7836: DAC Monitor

AMC7836: Switching between Closed and Open Loop

edward tregembo
Prodigy 20 points

Part Number: AMC7836
Other Parts Discussed in Thread: AMC7834

Is there a viable methodology to switch between open and closed loop operation with this device? Looking at implementing an Active Bias (Fixed Drain Current) but would like to disable (go open loop without updating the DAC) while RF is applied to the RF Amplifier. Essentially function as Fixed Gate when RF Applied, but be able to use the Active Bias for slower changes like temperature, aging. It appears viable in the datasheet except a note on page 82 of the datasheet, section 8.3.1, after note 11.

  • 0
    Prodigy 20 points

    My apologies Page 82 of the AMC7834 Datasheet. The part# in the title of this question is incorrect.

  • 0 in reply to edward tregembo
    TI__Guru 56843 points

    Hi Edward,

    This is possible, but might not be necessary.  Ultimately, you should consider if the RF signal being applied would greatly change the current measurement on average.  Note that the CSM inputs can CS-FILTER settings to allow a 25ms average, that might be enough to average out the power shift during the RF transmission period. 

    Otherwise you can disable the closed loop operation, and then restart it.  You do not necessarily need to CLAMP the outputs during this, but you should consider if there is any risks to the PA if the last closed loop update value is not ideal during the transmission. 

    It would also be possible to leave the device in open loop operation, but implement your own closed-loop with your host controller.  The host can monitor the CS values and update the DACs as needed.

    Thanks,

    Paul