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ISOW7841: using for isolated RS-485

KANJI SHIBATANI
Mastermind 6205 points
Part Number: ISOW7841
Other Parts Discussed in Thread: SN65HVD1781, , ISO3082, ISO3086T

Hello

My customer is designing for DMX /DALI application for lighting FY2019 model.

 

Do you have isolated RS-485 with DC/DC converter?

I am offering   customer as following .

( I like SN65HVD1781 dut to its high bus voltage )

MCU== ISOW7841==SN65HVD1781===> ( RS-485 line  > == termination

 

My concern is output available load current of ISOW7841.

I think it depends on application. But how do you think?

5V  : >130mA 3.3V: >75mA

Do you have any another idea for " RS-485 with DC/DC converter "?

Best Regards

 

  • 0
    TI__Expert 6195 points

    Hi Kanji,

    Thanks for bringing this question to E2E!

    There is actually a TI Design very similar to what you have proposed. This would probably be the smallest combination solution and the simplest design. 

    Another option to consider would be an isolated RS-485 transceiver and a discrete isolated DC-DC. See example below with ISO3082 and SN6505. 

    For an isolated DC-DC you could use a transformer driver like SN6505 and a transformer. The SN6505 can supply 1A with 5V supply, so you'll have plenty of headroom on that supply. You could even power a few other devices. 

    The downside with this solution is that we do not currently offer an isolated RS-485 transceiver with +/-70V bus-pin fault protection. There are discrete ways of implementing this (a combination of TVS diode and PTC fuse for example could accomplish this). 

    We also have a few devices with with a built in transformer driver such as ISO3086T. The transformer driver is integrated inside the device, so only an external transformer and (optional) LDO would be needed. This would again not be +/-70V bus-pin fault tolerant, but a discrete solution could be done. 

    Does this answer your question?

    Best regards, 

    Dan

  • 0 in reply to Dan Kisling
    Mastermind 6205 points

    Dear Dan-san,

    Thank you very much for your answer so immediately!!

    Its so helpful to start design for customer.

    After DIN, I may have futher question .

    Best Regards

  • 0 in reply to KANJI SHIBATANI
    TI__Expert 6195 points
    Hi Kanji-san,
    Glad I could help! This thread may lock by the time you have another question. If that happens, feel free to start a new thread and I would be happy to assist you further!
    Best regards,
    Dan