Hi all,

I am attempting to use the power down function (PD) of a fully differential amplifier (THS4552). The power down function works by pulling the PD pin to GND if you are using a single 5V supply OR if you are using a dual 5V supply by pulling the PD pin to the negative power rail. I would like to control the PD function with a PIC microcontroller and wanted to know the simplest options to bring the amplifier pin to GND and to -5V.

After a bit of my own research it seems an optocoupler could work fine for both. I sketched up a couple drawings of how I thought it would work, but I'm not sure if either version is correct. Any help is appreciated.

 

You can use an opto but it's not necessary unless you need galvanic ground isolation.

With a single supply, you can just drive the pin directly from the PIC.

With a plus/minus supply you can use a simple, one PNP transistor, two resistor, level-shifter circuit (below) where "In" is the PIC output and "/PD" is the power down signal to the amp.
/PD is -5V (powered down) with 0V input and ≈+0.6V (powered) with +5V input.
It reaches 0V output at about +2.6V input.

 

Thanks crutzchow. I was definitely overthinking the GND question. And yes that is a very simple way to accomplish the negative power down, exactly what I was looking for.