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  • TI Thinks Resolved

ISO7841: Using isolator to SPI lines

Part Number: ISO7841

Hi,

I have a little doubt about isolators and SPI lines. I need to communicate with four different ADS1299 sharing the same SPI line and with a baud rate of 15.6 MHz. I saw different texas isolators and the parameters are confusing me. I´m using 3V3 on both sides.

ISO7241M

Signaling Rate => Up to 150 Mbps 

Propagation delay => 16 ns (MAX), 10.8 ns (typical)

Pulse width distortion => 4.2 ns (MAX), typical 0.7 ns

Part-to-part skew => 4.5 ns (MAX)

Output rise/fall time => 0.8 ns (typical)

ISO7841

Signaling Rate => Up to 100 Mbps

Propagation delay => 32 ns (MAX)

Pulse width distortion => 2 ns (MAX), typical 1 ns

Part-to-part skew => 5 ns (MAX), typical 0 ns

Output rise/fall time => 2 ns (typical)

Both fulfill my requirements of isolation. I´d like to know which parameters I need to see in order to have that baud rate for the SPI. Signaling rate of the 7841 is lower than the other, but I think its parameters are better. 

Best regards,

Enio

Quad Channel, 2/2, 150Mbps, Digital Isolator

  • Hi Enio,

    ISO7841 belongs to one of our latest digital isolator families. It is designed to be a part far superior to the ISO7241. From SPI communication point of view, the data rate/rise fall times should be parameters of interest. As you mentioned, both the parts are capable of meeting said requirements for SPI @ 15.6MHz.

    I would recommend that the ISO7841 be considered for your application.

    Regards,
    Anand Reghunathan

  • In reply to Anand Reghunathan:

    Dear TI

    I have same question about ISOW7841 3.3V interface.

    i designed it with 5v power supply of ISOW7841 then use 3.3V interface voltage level of DSP(example tms320f28335).

    ISO7841W The part , i thinks the 3.3v signal is interfaceable. do you have any other advice for circuit?

    Best regards.

  • In reply to CHOI SEUNG WON:

    Hi Choi,

    Really sorry for the delay in responding to this.

    I understand that ISOW7841 is going to be configured for 5Vin 5Vout configuration. But it is going to be interfaced with 3.3V signal lines?
    Are these signals directly going to be interfaced between the DSP and ISOW7841? If it is direct, this may not work across different operating conditions.
    I recommend having a level translator in between.

    Regards,
    Anand Reghunathan
  • In reply to Anand Reghunathan:

    Hi Choi,

    It's been about a week since you've posted in this thread, so I'm going to assume we've resolved your questions about isolated SPI and ISOW. If this is not the case, please respond to this thread or open up a new thread. Thanks again for your question and have a great day!

    Best regards,
    Dan

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