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Original question:

AMC7904 Dac

AMC7904 interfacing

Louis Sankoorikal
Expert 2345 points
Other Parts Discussed in Thread: AMC7904, AMC7924

We are evaluating the TI AMC7904 for our TDD application where we require to control Gate Bias of 8 FETs. We were considering use of two TI AMC7904 devices to control the 8 GAN FETs.

To Save Space in RF section, we are evaluating if the two Drain Supply Switches (High current PMOS switch) which are controlled with the PA_ON signal of the AMC7904, can be replaced with a single Drain Supply Switch common to all 8 PA GAN FETs.

  • Need to understand if the above configuration will be supported by the two AMC7904 devices?
  • Can we combine the PA_ON control outputs of the two AMC7904 to control single Drain Supply Switch for the 8 PA GAN FETs?
  • In this case will the Power up and down sequencing of all the 8 PA GAN FET be complied with?
  • Please let us know your suggestion for this?

 We considered the AMC7924. However from checking the datasheet, we do not see support for TDD Switching control which we can see in the AMC7904 device.

  • 0
    TI__Guru 53333 points

    Hi Louis,

    1. Two AMC7904 could be sufficient for this application, depending on your switching requirements.  Note that each 7904 has two OUTx pins.  These pins can have fast Vgs-on to Vgs-pinchoff transitions, as well as fast Vgs-pinchoff to Vgs-on transitions.  The other two channels, DAC0 and DAC3, only have fast Vgs-on to Vgs-pinchoff transitions.

    2. The PA-ON pin is a push-pull design, so you should not short them directly together.  You could implement an AND gate on the two outputs, or you could connect the PA-ON output of one device to the ALARMIN input of the other device.  This would allow for a daisy-chain type configuration.

    3. If the two PA-ON outputs are AND'd, or they are daisy-chained, then it would still be okay for startup.

    The AMC7924 does not feature fast switching for TDD.  You would need external analog switches.

    Thanks,

    Paul