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SN65HVD1781D

MEL
Prodigy 10 points
Other Parts Discussed in Thread: SN65HVD1781, THVD2450, THVD2410

For a future development we want to combine the SN65HVD1781D  and another PHY for example another SN65HVD1781D . 

This means both ICs share the same connector and microcontroller UART interface.

 

But the individual power supply of each IC is switched. So only one IC is connected between the supply/connector and to the microcontroller at any time. 

Is this an allowed conditon?

Is it guaranteed, that the unpowered IC won't influence the data transfer of the other IC?

  • 0
    Guru 317360 points

    The bus pin are disabled and have high impedance when powered off; see section 9.3.3 of the SN65HVD1781 datasheet.

  • 0
    TI__Guru 52462 points

    Hi MEL,

    So the R, /RE, DE, and D pins all have an abs max voltage limit of -0.3V to VCC + 0.3V - this means that if VCC = 0V you cannot apply signals to those pins- you will destroy the IC.  So if the devices share the same UART controller interface both devices need to have active VCC to prevent damage. 

    The A/B pins are protected up to +/-70V regardless of VCC. If they are also sharing A/B connections - they will load the bus and will reduce the total number of nodes you can support - but it won't harm communication as the off device should be high impedance on A and B pins when VCC = 0V. 

    The THVD24x0 family of devices is the direct upgrade. 

    If your data rate is <= 500kbps than you could use the THVD2410 which allows its R, /RE, DE, and D pins to handle up to 5.7V on the inputs regardless of VCC; so using our more modern part you can achieve this goal (shared controller interface with only 1 IC powered). If your speed is > 500kbps than the THVD2450 would be the correct choice. 

    Please let me know if you have any other questions!

    Best,

    Parker Dodson