SN74LVC1T45: Need help with fully isolating ports A and port B (such as with optocouplers)

Karl Basker

Part Number: SN74LVC1T45
Other Parts Discussed in Thread: ISO7721

Hello,

We use SN74LVC1T45 in a trigger module for bus level translation.
Basically, the way as in datasheet Figure13. (Bidirectional Logic Level-Shifting Application)
In the current design VccA and VccB are not isolated sources. Also, both port A and B go to the ports of the same uC. Now we need to try it in a system that is particularly sensitive to noise and ideally I would need to use optocouplers to avoid transferring noise.

To do that, I need to have an isolated DC-DC converter, separate uCs for port A and port B. And it looks like I can't use SN74LVC1T45 for this tast as A and B share common ground. DIs my understandaing correct? Or maybe there is a simpler way to isolate A and B sides by using SN74LVC1T45 and without much redesign of my circuit?

Otherwise, does TI has other bus-translator ICs with fully isolated (optocoupled?) ports A and B?

Thanks in advance
Karl

over 5 years ago

0 Dylan Hubbard over 5 years ago

TI__Mastermind 45635 points

Hey Karl,

This device doesn't have true isolation, it seems like you need a digital isolator which TI also has. I'm moving your thread over to the appropriate team to help with this.

0 Lucas Schulte9 over 5 years ago

TI__Expert 6955 points

Karl,

The ISO7721 is a digital isolator that may interest you. It does need two seperate(isolated) power supplies for Vcc1 and Vcc2. The "21" in the ISO7721 means it has 2 channels in total with one channel going the oppposite direction of the other. Each channel is only unidirectional so you would have to use each of the 2 channels to achieve a form of bidirectional communication.

Respectfully,

Lucas

0 Karl Basker over 5 years ago in reply to Lucas Schulte9

Intellectual 385 points

Thanks Lucas,

Yes, it looks like I can stick to SN74LVC1T45 bus translator and add ISO7721. For bidirectionality, I can use the same logic that I use to control SN74LVC1T45. I am goind to use a DC-DC isolated converter which will give my 3.3V on the uC side. It seems to solve my issue ;)

Karl

Logic

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SN74LVC1T45: Need help with fully isolating ports A and port B (such as with optocouplers)