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How to connect SN65HVS885 input serializer to digital isolator

Ersan
Prodigy 90 points

Hi,

according to http://www.ti.com/lit/ds/symlink/sn65hvs885.pdf Figure(18)  an ISO7241 is used to isolate the SPI Pins. In Figure(19) a ISO7242 is used because CE got grounded and HOT (Temp. warning Flag) is a new input.

Why CE is got pulled down? I though its necessary to communicate?

What for an application design should I use now ? Figure 18 or Figure 19 ?  I want to cascade 3x HVS885 for our new PLC Input extension card.

Is it right that  If I use the ISO742x I dont need optocouplers on each input because the whole input part is isolated through it?!

Kind regards

Ersan

  • 0
    TI__Intellectual 970 points

    Hello Ersan,

    /CE is a clock enable "low" pin.  So grounding it will always have the serializer working off the clock source.  As far as the application, it depends on the information you want to communicate back to your controller.  For basic functionality, the /LD, CLK, and SOP are needed for communication.

    You are correct that you can replace opto's with one Isolated device, but you need a minimum 3-channel (or multiple 1 or 2 channel) isolators to get the basic Isolated HVS88x functionality.

    Regards,

    Bryce