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AFE20408: AFE20408 vs AMC7834 DAC current capacity for GaN Power amplifier

Ajay Chaitanya T
Prodigy 60 points
Part Number: AFE20408
Other Parts Discussed in Thread: AMC7834, , AFE10004

Tool/software:

Hi,

AMC7834 has +/- 10mA (source/sink) typical DAC current capacity whereas AFE20408 has +/-90mA typical DAC current capacity. 

My Doherty GaN amplifier needs max gate current of 50-80mA as per datasheet. But when i tested GaN amplifier in my board with bench power supply, gate current is around 1-2mA only. In this case, which bias controller should i select? Will the low gate current affect the GaN amplifier performance?

How important is gate current capacity for driving GaN vs LDMOS Doherty power amplifier?

  • 0
    TI__Genius 10400 points

    Hi Ajay,

    The high gate current is desired when using the PAs in a saturation mode, where the gate is set to a very high voltage to pulse as much power as possible through the PA. This can drive tens of mA. In general operation many PAs do not require high gate current. Note that the AFE20408 current limit can be set to other values, such as 30mA and 15mA (default). Your choice of controller depends on your design needs. 

    The AMC7834 is an older and larger device. It has a plethora of ADC monitoring inputs, but limited current capability, and only functions with SPI.

    The AFE20408 is newer and smaller, but limited in ADC inputs and no remote temperature sensing. The major inclusion for this device is internal switches for fast output switching. In particular, the output pins can switch between an "on" voltage and "off" voltage within a 400ns. This is desirable for designs that require the PA to be on and off in specific intervals.

    I recommended the AFE10004 in your other thread. This device is similar to the AFE20408. It has half the outputs but includes remote temperature sensing. it also has the internal switches. The biggest draw to this device is the autonomous capability. It has internal EEPROM that, once you program it once, will bias the PA gate according to the measured temperature. This is ideal for situations where you do not want to have a microcontroller on-board to monitor the temperature or PA controller.

    Thanks,
    Erin