Power and signal over one wire pair!!

Shrikant,

Please check out the XTR110, XTR111 and XTR300. All of these devices are so-called "three-wire transmitters." They are intened for equipment with a power supply (your 24V) and "push" a current output signal to a distant load. It would required two ICs to handle to separate signals.

Regards, Bruce.

Hi Bruce,

Thanks for the reply.

Actually three wires in my case are +24V, and two wires for two current outputs.

I found out that XTR115 can be use for this, but I don't have much experience on developing

Power and Signal on one wire pair so please let me know if I can get any design note for system design using these IC's.

Regards,

Shrikant. 

Hello Shrikant,

I think the above sketch will give you an idea. Hope I have understood your requirement correctly ?

Regards,

JayantD

Hi Jayant sir ,

The block diagram you have posted is exactly what I want to do.

For that I'm thinking of XTR115 but I would like to know how I can use same +24V for the remaining circuit which has DAC and controller.

As the GND required in this example is outside of the system, then how I can get the GND for the remaining circuit or I have to give GND as 4th wire.

If any note on this topic is available then please let me know.

Thanks and Regards,

Shrikant

Let's see what ti has to say..

Afterall, they have people who are paid to respond, isn't it ?

;-)

Please specify the voltage & current requirements of your remaining circuit ( DAC + Microcontroller) e.g. 5V 50mA etc..

Regards,

JayantD

Shrikant,

If Jayant's diagram accurately describes your situation then you want a 2-wire transmitter such as the XTR115. They will share the high-side positive power connection so that only three wires are used to connect to both transmitters.

The "ground" for each transmitter is actually a floating voltage, the Iret pin, that is unique to each transmitter. The Iret pins of each transmitter cannot be connected together. Imagine that all circuitry for each transmitter must be self-contained inside the box JC1 and JC2 respectively, as Jayant has drawn them. No additional power or ground connects to JC1 or JC2. All the additional circuitry inside JC1, for example, gets power from the Vreg or Vref pins of the XTR115. Its Iret pin serves as the floating "ground" of this additional circuitry. The total current consumed by your additional circuitry must be less than 3.5mA.

I hope you find this clear.

Regards, Bruce.

Hi Bruce,

Actually my current requirement is quite higher than you mentioned so I'll try to reduce it and let you know.

Mean while please tell me if there is any documentation on such a system development.

Regards,

Shrikant.

Shrikant,

Here is a link to various application notes and information on 4-20mA loop circuits:

http://www.ti.com/analog/docs/analogtechdoc_hh.tsp?viewType=mostuseful&techDoc=1&rootFamilyId=57&familyId=508&docCategoryId=1&Input3=Go

I think that some general reading in this material will give you some good background.

... and here is one, specifically that adds front-end signal processing ahead of the XTR115.

http://www.ti.com/litv/pdf/sboa107b

Keep in mind as you read this app note that the ground symbols on the left side of the XTR115 are "local grounds" that can only connect to the Iret pin of the XTR115. They cannot connect to ground on the receiving side of the loop (to the right of the XTR115).

Regards, Bruce.

Hi Bruce,

Thanks for the information.

I'm going through these documents and will built prototype for xtr115.

Can you suggest me some of the low power micro-controllers from TI having  inbuilt DAC.

I'll let you know if I get any difficulties.

Thanks and Regards,

Shrikant.

Bruce,

I'm unable to get anything useful from the first link.. it opens a general search page! Will you please look into it ?

In case the external circuitry draws more than 3.5mA, will it help to power this by a battery, with the battery negative connected to IRet ?

Thanks,

JayantD

Shrikant and Jayant,

Here two app notes that may provide some background insights into 4-20mA loop applications:

http://www.ti.com/lit/an/sboa017/sboa017.pdf

http://www.ti.com/lit/an/sboa025/sboa025.pdf

Both of these application notes are older vintage and may refer to products that are not the most modern or cost effective devices. Use them for ideas.

The MSP430 family of micropower microcontrollers offers a wide range of performance and features, including on-board data converters. There is a specific E2E forum supporting these devices and they are the best experts to help you select a product.

Yes, it would be possible to use a battery to power additional circuitry on the input side of the XTR115. For additional positive supply voltage and/or power, the negative battery terminal should connect to the Iret pin.

Regards, Bruce.