SN65HVD485E failsafe circuit

na na78

Other Parts Discussed in Thread: SN65HVD485E

We have a question for SN65HVD485E failsafe features.

We are going to have external open, idle failsafe bias circuit, but SN65HVD485E seems to provide internal biasing feature for open-circuit, bus-idle, or short-circuit failsafe conditions.

Should we have external failsafe bias circuit?

(We want to have up to 32 unit load on bus.)

regards,

over 9 years ago

0 Michael Peffers over 9 years ago

TI__Mastermind 20820 points

Hi Na Na,

It is OK to implement an external failsafe circuit with devices that have an internal failsafe circuits. The bias point will only shift slightly depending on the value of the failsafe resistors that you use. Please let me know if you have any questions?

0 na na78 over 9 years ago in reply to Michael Peffers

Guru 16770 points

Hi Michael

Thank you for your reply.

We have additional questions.

1. How to calculate external failsafe bias resistors (R1, R2)? We assume RT=120ohm and the network like following figure.

2. Does the number of nodes affect the resistor value? We assume the number of node up to 32.

3. SN65HVD485E provides internal biasing for open-circuit, bus-idle, or short-circuit. So, doesn't it be problem without external failsafe bias resistors?