Circuit Diagram

My question is: Does this circuit isolate the "X Volts" lines from ground (1) If not, how should I implement an opto-coupler to provide isolation between the data lines ("X Volts") and ground? (Question 1 - Main question)

I briefly looked up the datasheets for both the BAW56 and the GL05T

The BAW56 is a high-speed switching diode? Is this for when one line is in use it will close the other line? (Question 2)

and the GL05T is for ESD/groundloop protection is this correct? (Question 3) It looks like Unidirectional Clamping as shown in the datasheet. So this means no current can pass FROM ground, and only current can pass TOWARD ground once the zener is satisfied?

It doesn't seem to be isolated because I don't see any opto-couplers involved.

Further information:

  • "X Volts" lines are data lines pulled up (with resistors) to 3.3v

1 Answer 1


It's simply ESD protection for both of those X data lines. Nothing more.

The GL\$05\$T provides protection against positive transients that exceed the \$5\$V avalanche breakdown of that device, and the BAW\$56\$ signal diodes provide protection for negative transients below the Vf of that diode, which is about \$0.7\$V, so they would start to conduct for any negative transients that exceed \$-0.7\$V.

It's not an isolation circuit, as there is a clear path to ground, therefore it is not isolated, by definition.

how should I implement an opto-coupler to provide isolation between the data lines ("X Volts") and ground

It's not entirely clear to me what you want to do here, since you have provided too little information about the signal on the "X Volts" lines. If you want to isolate a signal, then there are plenty of opto-isolated signal examples to be found on the web, and the signal lines before the opto-isolators might still require the same ESD protection as your post shows, but you would not send transients into the signal ground, they must only go to the protective ground.

For fast differential signals, you will want to use a digital isolator, such as the Analog Devices ADuM\$1100\$ or ADuM\$1200\$ and friends. Optocouplers are generally too slow for this. For a bidirectional bus like USB you must use a specialized isolator like the ADuM\$4160\$.


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