opto isolator IC for DSP

[sandip_]

Hi all,

I am working with DSP interfacing, I need to isolate sensor outputs form the ADC input pins of DSP. Can some one suggest an opto isolator IC for that. I mean that should work in the range below 2v..because the DSP has max capability of 3.3 volts.

thanks a lot

 

[shaiko]

You want to measure the voltage of the pins you're isolating from the ADC?

You'll need a very linear optocoupler...
What accuracy are you looking for?

 

[sandip_]

thanks for the reply
Actually I am new to this opto isolater terminology.
what I need is ..I need to give my voltage sensor output to ADC, so that I can further process it in DSP. my sensor receives the 230v/50hz sine waveform voltage and outputs it, in the range of 0 to 2.2 volts.Since the DSP I am using works for 3.3 volts max, the output values of my sensor will suit for my ADC as inputs( which is an internal part of my DSP(TMS320F28335))..till now everything is fine.

But, my guide asked me to isolate the sensor outputs form DSP. so that, any wrong in my power circuit wont damage the processor.
hence I need an opto isolator IC for that and coming to accuracy, I dont know much.

but in my lab I have MCT2E, I dont know whether this will work for that purpose or not.

.. I am a bit lenthy..sorry!!

 

[shaiko]

I'm no analog expert - but using an galvanic isolation on a voltage that you intend to measure accuratly doesn't sound like a very good idea.
Any non linearity of the optocoupler will translate to inaccuracy in the ADC reading...
A transformer may do better - but again I'm not an analog expert.

Anyways, why not simply protect against over voltage?

 

[Nasser750gx]

Dear Sandip,

Even if you use Optocoupler, you must choose a one which is socket compatible, otherwise if the optocoupler burns, it will render the PCB vague (unless you can manually replace the optocoupler, or willing to send the board for RMA and a session of high-temperature exposure).

I would suggest a Capacitor voltage divider (since it's AC you're interested in). In this scenario, the impedance of the capacitors in a resistor-like voltage divider, will ensure good isolation from the power-parts while bringing the voltage range down to an acceptable level (1/200 would be helpful, since it brings 230V down to 1.65V. To reach 3.3V, you would need 460V).


Good Luck

 

[pradhan.rachit]

You might consider using the IL300 which is a linear opto-isolator IC.
You will require 2 isolated supplies to power it up. A normal opto-coupler such as the MCT2E will fail in your application due to it's non-linear nature.
I have used the IL300 in the positive unipolar photo-conductive mode given in Vishay's application note 50 which is interfaced with a TMS320F28027 Piccolo Launchpad.

You can find more details on:

www.vishay.com/docs/83708/appn50.pdf

Regards

Rachit