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Original question:

AFE20408: Output switch and drain switch control

AFE20408: DAC vs OUT

Ajay Chaitanya T
Prodigy 60 points

Part Number: AFE20408

Tool/software:

In my design, AFE20408 has to drive gates for two GaN Doherty, one LDMOS Doherty devices i.e., 6 gate voltages. I am planning to give VSSA negative voltage and VCCB positive voltage. I want to use {OUTA0, OUTA2}, {DACA1, DACA3} (additional gate biasing in application notes sbaa621) for GaN (4 gates) and {OUTB0, OUTB2} for LDMOS (2 gates).

Can DACA1, A3 drive gates ON/OFF similar to OUTA0, A2? What should i have to take care when i'm using DACA1, A3 for gate biasing along with OUTA0, A2? 

  • 0
    TI__Mastermind 42253 points

    Hi Ajay, 

    Erin will review your use case and respond with some feedback soon. 

    Best,

    Katlynne Jones

  • 0 in reply to Katlynne Jones
    TI__Genius 17110 points

    Hi Ajay,

    When using the DACA1/A3 for additional gate biasing, here are the main points you should be aware of:

    The OUTA0/A2 pins must use VSSA as the "off" voltage in this configuration. You will have the fast on/off switching between DACA0/A2 and VSSA. 

    The DACA1/A3 outputs can turn on and off through the DRVEN pins or bits, similarly to the OUT outputs. This turns on and off the DACA1/A3 buffer, giving you switching between DACA1/A3 and VSSA. Turning the DAC off (to VSSA) will be fast. Turning the DAC back on will be slow (around 3us as opposed to 100ns). You can see this behavior in Figure 3-6 in the application note. I would recommend setting the DACA1/A3 outputs to gates that do not require fast on timing. Additionally, use a small (or no) capacitor on the DACA1/A3 output to assist with fast off switching.

    Let me know if you have any other questions.

    Thanks,
    Erin