SN65HVD379: What purpose of output side pull up/down resistor?

Paul Yeh

Part Number: SN65HVD379

Tool/software:

Hi team,

See an article on TI Forum. Someone add pull up resistor(4.7kohm) and pull down resistor(2.7kohm) over the differential signal.

What are these resistors for?

https://e2e.ti.com/support/interface-group/interface/f/interface-forum/742224/sn65hvd379-sn65hvd379-interfacing-diagram

Thanks

over 1 year ago

0 Clemens Ladisch over 1 year ago

Guru 327050 points

These fail-safe resistors generate a differential bus voltage of +44 mV when the driver is inactive (disconnected or powered down). These resistors are too weak; the datasheet requires a voltage of at least 200 mV.

(Only one set of fail-safe resistors is needed on a bus. With RS-422, the termination resistor should be present only at the receiver, i.e., R24 should be removed.)

+1 Ethan Sempsrott over 1 year ago

TI__Mastermind 29632 points

Hi Paul,

I agree with Clemens. Here is this article on failsafe resistors for more information: https://www.ti.com/lit/an/slyt324/slyt324.pdf

Let us know if you have any other questions!

-Ethan

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SN65HVD379: What purpose of output side pull up/down resistor?