PWM control of XTR115U to get 4-20mA

shivakumar L V67

Other Parts Discussed in Thread: XTR117, XTR115

I would like to interface the XTR115 to a standard 3.3V or 5V MCU pin with PWM(isolation required). can any one provide working circuitary?

over 9 years ago

0 Michael Peffers over 9 years ago

TI__Mastermind 20820 points

Hi Shiv,

I am moving this post to the amplifiers forum as they have answered questions related to the XTR117 in the past.

0 Collin Wells over 9 years ago in reply to Michael Peffers

TI__Guru 62915 points

Hello,

See parts 4 and 5 of a recent blog series we published on 2-wire 4-20mA transmitters. Both blogs show a solution using the ISO7310 to properly isolate a PWM input signal for use with 2-wire 4-20mA transmitters such as the XTR115.

0 Collin Wells over 9 years ago in reply to Collin Wells

TI__Guru 62915 points

One more thing, you'll need a buffer amplifier between the Rin resistor and the Ros/Iin connection to prevent interactions between the PWM filter and the input impedance of the XTR115.

0 Willem van Peet over 7 years ago in reply to Collin Wells

Prodigy 30 points

Hi Collin

What is the minimum impedance required after a pwm filter, to be sure not to interfere with the XTR115 input impedance?

Furthermore I'am having trouble with our XTR115 it gives an 31mA output, when trying to give it a input on Iin, if Iin pin is left floting the XTR115 output is normal. When the input on Iin is only 40µA from a 60k ohm resistor connected to Vref it also outputs 31mA?

Kind regards Willem

0 Collin Wells over 7 years ago in reply to Willem van Peet

TI__Guru 62915 points

As shown in the blog and mentioned in some other posts you'll need to buffer the output of the passive PWM filter otherwise it will alter the input impedance of the XTR circuitry.

Also, please open a new thread for your other XTR115 questions.

0 gaston vallasciani over 7 years ago in reply to Collin Wells

Prodigy 95 points

Hello Collin,

I use those documents you write to design a 4to 20mA loop transmitter , but those documents aren't in the page anymore. Can you send them to me ?

Regards,
Gastón

0 Collin Wells over 7 years ago in reply to gaston vallasciani

TI__Guru 62915 points

The blogs are linked three or four posts back in this thread. Here's an example schematic that's been shared on a few other forum threads that you can search for and locate.

Because of the holidays, TI E2E™ design support forum responses will be delayed from Dec. 25 through Jan. 2. Thank you for your patience.

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PWM control of XTR115U to get 4-20mA