ISOM8711: Opto-Emulator - "Normally switch"

Ohad Bonneh

Intellectual 1970 points

Part Number: ISOM8711
Other Parts Discussed in Thread: ISOM8110, ISOM8610,

Tool/software:

Hi Team,

I'm looking for an isolation device that will replace a relay,

The opto - emulators can be a good fit here, however, we want to be able to make it switch normally meaning that when we don't drive any current the opto - emulator is closed or logic low

and vice versa, when we drive current on one side, we are getting logic high on the other.

Do we have such a feature?

Thanks!

6 months ago

0 Clemens Ladisch 6 months ago

Guru 317480 points

Relays are slow; why are you trying to use a high-speed device?

Phototransistor optocouplers and their replacements like the ISOM8110 can be used with a pull-down resistor at the emitter.

0 Ohad Bonneh 6 months ago in reply to Clemens Ladisch

TI__Intellectual 1970 points

In terms of speed the ISOM8110 can be good for us,
can you explain in details regarding the pulldown resistor at the emitter? how would that translate to "normal switching" like device?

0 Clemens Ladisch 6 months ago in reply to Ohad Bonneh

Guru 317480 points

0 Varun Kumar 6 months ago in reply to Ohad Bonneh

TI__Expert 8430 points

Hi Ohad,

If you're looking for an opto-emulator as a replacement for relays, then my recommendation would be using ISOM8610 : ISOM8610 data sheet, product information and support | TI.com

This has very good EMC compliance, fast switching, high BW and low COFF.

Regards

Varun

0 Ohad Bonneh 6 months ago in reply to Varun Kumar

TI__Intellectual 1970 points

I need it to be NC without any voltage applied

Also switch should be bi-directional as SSR

0 Clemens Ladisch 6 months ago in reply to Ohad Bonneh

Guru 317480 points

There is no such device.

0 Koteshwar Rao 6 months ago in reply to Ohad Bonneh

TI__Guru 55815 points

Hi Ohad,

As others have responded, we don't have a "Normally Closed" opto-emulator. The closest device to replacing a bidirectional relay is ISOM8610 but this is "Normally Open".

If this question is in relation to your other E2E post (click here) to enable/disable the outputs of a digital isolator, then the circuit that Clemens proposed can work fine with both ISOM8110 and ISOM8711. For your reference, I am copying below the circuit. The OUTPUT pin can be connected to EN pin for enabling/disabling the outputs. The outputs will normally be disabled and need to be enabled by driving ISOM device.

Regards,
Koteshwar Rao

Isolation

Isolation forum

ISOM8711: Opto-Emulator - "Normally switch"