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SN75176B: what's the apply difference between DS75176B and SN 75176B

Damien Zhang
Intellectual 1175 points
Part Number: SN75176B
Other Parts Discussed in Thread: SN65HVD485E

dear all,

due to DS75176B stop produce, i directly change it with SN75176B in my application. but i found PIN1 will output noice data then A and B no any input or output. my schematic as below pictures, just add an isolation device before RS485 data output from 

i need to know what's the different at the application between SN75176B and DS75176B? could you please recommend a hero part number to replace DS75176B?

thanks so much. :)

  • 0
    TI__Intellectual 1175 points
    i found if i use sn65hvd485E to replace DS75176, it could work normally and no noise data in PIN1. could you please help check may i directly replace and needn't change any design in my schematic?
    thanks so much.
  • 0 in reply to Damien Zhang
    TI__Guru 62920 points
    Hi Damien,

    It is OK to use SN65HVD485E as a drop-in replacement for DS75176 without changing the schematic. It should be OK to drop in SN75176B as well, though, since these two devices have the same function and are very close in parametric performance.

    In this case, when A and B have no input then the differential voltage between them is likely close to 0 V. This results in an undefined output for SN75176B since its high/low switching threshold for the differential input is close to 0 V. I would expect DS75176 to have a similar limitation, although this is something that may vary slightly from unit to unit. The SN65HVD485E has an input switching threshold that is slightly negative so that a disconnected input will reliably be interpreted as a logic high level on the R output. This is often referred to as failsafe biasing, and you can see it reflected in the VIT+ and VIT- specifications of a transceiver. If your application requires a constant high output when no differential signal is present on the input, then using a transceiver like SN65HVD485E with internal failsafe biasing is a good way to go. You could also implement failsafe biasing externally if you wished. Here is some more info on that:

    e2e.ti.com/.../rs-485-basics-two-ways-to-fail-safe-bias-your-network

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    TI__Intellectual 1175 points
    thanks so much for your reply :)