Question: I have an analog motor controller that has a B10K potentiometer on it. I'd like to be able to swap out the analog potentiometer for a digital one, but I'm not exactly sure what voltage is being sent to the original potentiometer as I don't have the spec sheets for it.

My current specifications, which work as a prototype, are:

```
- Power supply: 48V 4A transformer, connected to...
- Variable speed DC PWM Motor Controller which controls...
- A 130V 1A max DC motor. 

```

I'm fine with the power and speed that 48V gives me, but do I need to specifically look for a digital potentiometer that can handle high voltages, or would a standard 10K digital pot work?

Answer: 
You can increase the voltage drop and use a (very efficient) DC-DC converter to convert the higher voltage drop to a higher current. For example, if you need 3V at 20mA (60mW) you could drop 17V or so and if your DC-DC is efficient enough you will stay under the 4mA. Chances are you will have to design this, most chips and modules use too much quiescent current to make this work. 

Optionally, and this is common practice if you are not even close on the current, is to use an external supply and DC-DC isolation to provide the necessary current. There are many kinds of devices that cannot operate from the small amount of power in a loop-powered instrument. Of course it increases the wiring cost and may make intrinsic safety more complex. 

Another option (probably less popular these days) would be to use a different analog current loop standard such as 10-50mA.
When designing a transmitter with the XTR115/6 your options are limited by the chip specifications. In particular the 5 volt regulator output current is limited to < 12 mA. There is a knee in the voltage output at 1 mA of current where it drops to about 4.5 volts where it remains up to Imax.

You will find that if you are designing industrial 4-20mA devices, this is about the maximum power budget you have available since the loop specifications are made to limit power for intrinsically safe environments.

Note that if instead of using the internal regulator, you add a buck converter to your circuit, for example, you are adding "energy storage" devices to the design which will force you to go through certification if you desire an IS rating. If you already have other "non-simple" devices in your design, this may not be a deciding issue.

Edit:

You may find [this](http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=slyt488) app note from TI regarding harvesting energy from a 4-20 mA loop applicable to your situation. They walk through a design using a TPS62125 to provide a 10 mA supply with some higher peak current capabilities.