SN65HVD52: open circuit failsafe

Masaoki Koide

Intellectual 580 points

Part Number: SN65HVD52

Dear Sir,

Our customer are using TI RS-485 driver/receiver SN65HVD52 for their application.

Due to the application reason, SN65HVD52 powered 5V is mounted on the board without input and output signal.

How should we treat input/output pins in this situation for failsafe? Is leaving them open OK or not?

Regarding the datasheet, it seems that the device supports "Bus Idle, Open, and Short Circuit Failsafe",

but I can't find out the details about it.

Your kind advice would be really appreciated.

Regards,

Koide

over 6 years ago

0 Hao L over 6 years ago

TI__Mastermind 25705 points

Koide,
There are on-die pull down resistors for RE and D pins, and pull up for DE pin. RX input threshold was designed to be failsafe when the bus is idle - RX output keeps high in this case.
Regards,

0 Masaoki Koide over 6 years ago in reply to Hao L

Intellectual 580 points

Hi Hao,

Thank you very much for the advice. It looks that there's no enable pin in SN74HVD52 (always enabled). In this case, can we treat the same as you mentioned? - A &B : No treatment needed, R : High. How should we treat for Tx input and output (D, Y and Z)?

Regards,
Koide

0 Hao L over 6 years ago in reply to Masaoki Koide

TI__Mastermind 25705 points

Koide,
D has internal pull down by default. Y and Z are output pins, which should not have failsafe concern. When Vcc is provided and Tx input is floating, Z will be pulled high and Y be pulled low.
Regards,

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SN65HVD52: open circuit failsafe