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THVD1424: THVD1424

Cedric Tornesi
Prodigy 40 points
Part Number: THVD1424
Other Parts Discussed in Thread: SN74LVC1G04

Tool/software:

Dear TI Support Team,

Concerning THVD1424 Receiver side:

When the cable is unconnected or driver is unconnected/disabled, the Receiver does output a '1' on R (Open or idle bus failsafe event), Ok. As I want to avoid this effect,

I did put 100k to Ground on each wire of the Receiving pair  but the output "R" is still at '1'. I think it is because the bus is not actively driven as said in the datasheet.

Would I have a '0' on R with lower (around 1k, maybe lower ?) pull-down resistors on each node of hte Receiving pair ? Or do I need to have a higher bias voltage on the signal minus than on the signal plus to have an active driving ? (as an example, with a pull-down on the +, and a pull up on the - ?)

I thank you in advance for your support 

Regards,

Cédric

  • 0
    Guru 316690 points

    To get a low fail-safe output, exchange the A/B pins and add an inverter (e.g., SN74LVC1G04).

    Alternatively, make the bias resistors strong enough that you get more than −200 mV over the termination resistors. With a 3.3 V supply, this should be 2× 390 Ω or lower. (And in a standard RS-485 system, there might be other bias resistors going in the opposite direction at some other place on the bus.)

  • 0 in reply to Clemens Ladisch
    Prodigy 40 points

    Clemens,

    I thank you very much for your answer !

    Regards,

    Cédric