ISO7720: Opto Coupler Replacement

bhupendra suthar

Intellectual 505 points

Part Number: ISO7720
Other Parts Discussed in Thread: ISOM8710, ISO6441, ISO6741, ISO7741, SN74LVC1G34

Tool/software:

TI Team,

Good Day !

Our industrial control board has High Speed Opto Coupler Like HCPL-0631 / TLP2662.

We are Looking to find substitute for it. Going through Research we knew Digital Isolator and Opto-Emulator.

Can you Suggest which is better option to go with ?

Main Focus is : Less Discreet Component and Space without compromising design Robustness.

Also , one concern is Load Driving capacity of the device. Currently it is 15mA.

You can suggest any document to design Robust circuit with Isolator / Opto-Emulator.

Best Regards,

Bsuthar

2 months ago

0 Clemens Ladisch 2 months ago

Guru 316420 points

An opto-emulator has an input that behaves like a IR-LED; it is designed to be a P2P replacement for optocouplers. See the ISOM8710/8711.

A digital isolator requires a separate power supply for the input side, and has logic (high-impedance) inputs. In general, a digital isolator is easier to use if you are designing a new board.

0 Aaditya V. 2 months ago

TI__Genius 17275 points

Hi Bhupendra,

Thanks for reaching out.

Clemens is correct. if you would like to have a pin-to-pin replacement solution, the ISOM8710 or the ISOM8711 are recommended.

As Clemens stated, implementing a digital isolator may take a few extra steps to implement a separate power supply and logic signals. Below are some recommendations of digital isolators:

ISO6441, our newest generation digital isolator, which supports 100Mbps data rate, overvoltage tolerant inputs: https://www.ti.com/product/ISO6441
ISO6741, which support 50Mbps data rate, wide supply range 1.8-5V: https://www.ti.com/product/ISO6741
ISO7741, which supports 100Mbps, various package options: https://www.ti.com/product/ISO7741

Please keep in mind that these digital isolators have many channel count options. To see more digital isolator options, please see https://www.ti.com/isolation/digital-isolators/products.html

For future cross references: https://www.ti.com/cross-reference-search

Regards,
Aaditya V

0 bhupendra suthar 2 months ago in reply to Clemens Ladisch

Intellectual 505 points

Thank you, Clemens

Any thought on Load Driving capacity , which is good one , Isolator vs Opto Emulator ?
Would Opto Emulator need same discreet component like we use for Normal Opto Coupler ?

0 bhupendra suthar 2 months ago in reply to Aaditya V.

Intellectual 505 points

Thank you, Aditya

Data rate with Me is 1 Mbps.

Can you point out any docs/ schematics for Digital isolator based robust design ?

Regards,

Bhupendra

0 Aaditya V. 2 months ago in reply to bhupendra suthar

TI__Genius 17275 points

Hi Bhupendra,

Since you need 15mA, digital isolators may not be a suitable solution for your system. There are 2 options that you can consider:

ISOM8711, which is an open collector opto-emulator, P2P with the competition device you mentioned earlier.
ISO1641, which is essentially a open-collector digital isolator. This is typically meant for I2C applications, but this will allow for your output drive current to be higher and could also be suitable for your application.

Regards,
Aaditya

0 Clemens Ladisch 2 months ago in reply to bhupendra suthar

Guru 316420 points

Digital isolators do not support 15 mA; a typical drive strength is 4 mA.

Where does the 15 mA requirement come from? This is the output capability of an open-collector optocoupler, but this current is usually not used in actual circuits. If you want to replace an optocoupler without redesigning the circuit, use an ISOM device. If you are creating a new circuit, it is unlikely to require 15 mA. (If you really require 15 mA, you can add a buffer like the SN74LVC1G34 after the isolator.)

0 bhupendra suthar 2 months ago in reply to Clemens Ladisch

Intellectual 505 points

Yes, Clemens , It is Open Collector opto Only.

Since , Distance is 1 meter and Datarate ( ~1Mbps ) , Current driving capacity @5VDC is desirable.

Yes, Using Buffer at output works....But space..:)

BTW, Currently we are using Buffer between MCU O/p ( 3.3V ) and Opto-Coupler I/P, Do we need to use buffer IC for the input of the Digital Isolator if we replace ?

Regards,

Bhupendra

0 bhupendra suthar 2 months ago in reply to Aaditya V.

Intellectual 505 points

Okay Aaditya,

We will see implementation.

Can we directly Drive any Digital Isolator directly from MCU Pin ( 3.3V ) ? Any Series RES / Buffer to use....

Regards,

bhupendra

0 Clemens Ladisch 2 months ago in reply to bhupendra suthar

Guru 316420 points

A digital isolator would not need a buffer at its input; it is designed to handle logic signals directly.

If you really need high drive strength at the output, use the ISOM871x. Do you really need an open-collector output? The push/pull output of the ISOM8710 would be more robust.

0 bhupendra suthar 2 months ago in reply to Clemens Ladisch

Intellectual 505 points

Hello Clemens,

Open Collector not necessary. we will tried out with your suggestion.

I believe, Suggested Opto-Emulator can directly drive from 3.3V MCU pin , without buffer IC like you said for digital isolator , Correct ?

Any docs/ Reference design for Digital isolator/Opto Emulator based robust design would be helpful.

Regards,

Bhupendra

0 Clemens Ladisch 2 months ago in reply to bhupendra suthar

Guru 316420 points

The ISOM871x requires an input current of at least 2 mA. Your MCU should be able to drive this.

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ISO7720: Opto Coupler Replacement