ISO7742: Isolating bidirectional signals

HS FAE Germany

Part Number: ISO7742
Other Parts Discussed in Thread: TUSB2551A,

Hello,
is it possible to isolate bidirectional signals with the ISO7742? Customer wants to isolate signals (VP, VM) between MPU and USB PHY (TUSB2551A). Direction signal OE^ is available.

Regards, Holger

over 9 years ago

0 Anand Reghunathan over 9 years ago

TI__Intellectual 2900 points

Hi Holger,

Yes, it is possible to use a digital isolator to isolate bidirectional signals. Please refer to Designing an isolated I²C Bus^® interface by using digital isolators.
Two digital isolator channels would be required to realize one bidirectional channel. ISO7742 can be used to realize two bidirectional channels using this approach.

What is the data rate you are planning to operate at? ISO7742 is capable of operating at a maximum speed of 100Mbps.

Regards,
Anand Reghunathan

0 HS FAE Germany over 9 years ago in reply to Anand Reghunathan

TI__Mastermind 32930 points

USB FB is 12Mbit/s.
I think I don't need the workaround with the transistor if I have a direction signal? I could connect it to EN1 and EN2, right?

Regards, Holger

0 Anand Reghunathan over 9 years ago in reply to HS FAE Germany

TI__Intellectual 2900 points

Hi Holger,

I am not clear on how this is going to be achieved.
I'm assuming that the OE signal is coming from the MPU to the USBPHY, which would also require an isolated channel for communication.
In order to ensure this communication is uninterrupted even when the digital isolator is disabled, it would have to be routed through a separate isolator. Please see example image below.

Could you please confirm if this is the methodology you had in mind?

Regards,
Anand Reghunathan

0 HS FAE Germany over 9 years ago in reply to Anand Reghunathan

TI__Mastermind 32930 points

Hello Anand,
yes, this is what I had in mind. I will discuss this with my customer.

Regards, Holger

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ISO7742: Isolating bidirectional signals