double/dual 4-20 mA output with µController

Erik,

As far as fully integrated options go the available products from TI include the DAC8760 family (DAC8760, DAC7760, DAC8750, DAC7750) which includes 16-bit and 12-bit variants as well as options with or without a voltage output as well. These devices implement both a DAC and a high-side voltage-to-current converter. These parts are not sink architectures nor loop powered architectures like the XTR115 - these are sources intended for 3-wire or 4-wire analog output architectures.

There is another device with 4-channels, an integrated buck-boost converter, and a current output stage which can both source and sink current called DAC8775 which has recent entered preview status. Similar to the DAC8760 family, though, this is targeted for 3-wire or 4-wire applications, not a loop powered application like the XTR115.

You could use a discrete op-amp design like what is shown in TIPD101 or TIPD102 for each high-side and low-side current structures for 3-wire applications, but yet again this is not exactly a loop powered design like XTR115.

TIPD158 shows a discrete op-amp based design that is basically equivalent to the XTR115 along with a discrete DAC which you could replace with a PWM-based solution. The XTR115 has sibling devices in the XTR116 and XTR117, these variants are according to the reference voltage value and/or presence of a reference voltage.

Based on your post, I'm not totally certain of exactly what you're looking for. If you could describe the terminal connections you would expect your end design to have, perhaps I can help better.

Hey Kevin,

thanks for this fast reply! It already helped me a lot. I was wrong, XTR115 is already a sink type signal transmitter. Just to repeat: the DAC8760 family is completely source type, so I cannot use them. DAC8775 looks really good, but it is not a finished product yet?

So the best posibility is XTR115 (or 116/117)?!

I want to read a sensor signal (not yet definied; 0,5 - 4,5V; 0 - 10V; 4-10 mA) with AI of a µController (Arduino). These signal shall be transformed to a dual/double 4-20 mA signal. At least one of the outputs needs to be passive/ sink type. So I can smooth the PWM signal of µController and use this signal to control XTR115.

Erik,

DAC8775 releases tomorrow.

XTR115 or the others in that family are good choices for integrated voltage-to-current converter solutions. I did forget to mention DAC161S997 in my previous post, this is basically a PWM DAC + XTR115.

A dual-channel structure using XTR115 or DAC161S997 (or the TIPD158 approach I mentioned) will require channel-to-channel isolation. These devices control loop current basically through their ground planes. It is not possible to have two channels without isolation.

Hi Kevin,

thanks again for fast reply! What is/will be the price for a DAC8775?

Excuse me I am not that good in electrotechnics :) what means channel to channel isolation in this case? Would it be okay, to use 2 seperate PWM output pins of a µController with the same ground pin? Or do I have to use 2 seperate µControllers with seperate power supply? Or do I have to use an optocoupler?

Or do you mean, the power supply for each current loop (4-20mA) needs to be independet?

Erik,

A 2-wire design like what you would realize with the XTR115 regulates the current flowing into the design's ground. Therefore a dual-channel design would require two separate ground loops. You could use the same MCU to provide a PWM, but there would need to be digital isolation on this PWM line as well as an isolated power solution to completely separate the two loops.

My colleague wrote a multi-part blog series on 2-wire transmitters that might help clarify this some. I picked a few particular blogs that I think would help you with this particular topic: