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AMC7834: AMC7834 AUXDAC and DAC port usage

SOORAJ SUNDARAN
Prodigy 20 points
Part Number: AMC7834
Other Parts Discussed in Thread: LM50

We are using the AMC7834 for the TDD application radio unit, 

As per the below block diagram, we will having the requirement od 8 DACs including the 4 AUX DACS,

Could you please provide answers to the following questions,

  1. what is the speed of operation difference for the AUX DAC and the DAC?
  2. Can we dedicate the AUX DAC ports only for the Driver amplifiiers?
  3. Can we use the AUXDAC ports for the PA biasing?
  4. Is there any provision inside the AMC7834 to make the bias voltage for the respective DAC port to 0V suddenly, we need this feature for the RX event 
  5. What is the response time for the DAC upon command input?
  6. What is the response time for the AUXDAC upon command input?
  7. is there any closed loop system can be done withe LM50 tenperature sensor and the AMC7834 as standalone?

  • 0
    TI__Guru 53773 points

    Hi Sooraj,

    1. The settling time for both AUXDACs and DAC outputs are the same.  They have similar AC behavior.

    2. These DACs can be used for any biasing, but the clamp mode only makes the AUXDACs go to GND.  The regular DACs have the VCLAMP inputs  for programmable clamp voltages.

    3. You can for LDMOS type PAs.

    4. The CLAMP functions are somewhat slow as the internal analog switch has some impedance.  We specify about 5µs for CLAMP functions.

    5. The latency updating the DAC is very short.  So consider the LDAC event starts with the rising edge of CS during an update command.  You can expect that to start slewing in a few hundred nanoseconds.  The real delay is the slew rate and settling time.

    6. The DACs and AUXDACs have the same update time.

    7.  The device cannot monitor external temperature sensors for a closed loop operation.  Any closed loop functions would be require the host controller to monitor the ADC inputs and directly update the DACs.

    Thanks,

    Paul