SN65HVD3082E: Bias resistor for the external fail-safe circuit

K.Hamamoto

Guru 12155 points

Part Number: SN65HVD3082E

I would like to know about bias resistor of the external fail-safe circuit such as the following circuit.

We should choose the resistor(above R) to be more than 200mV between A and B. Is my understanding correct?

If it correct , is there any recommend value?

Best Regards,

Koji Hamamoto

over 5 years ago

0 Hao L over 5 years ago

TI__Mastermind 25705 points

Koji,

Your understanding is correct. Basically there are two criteria for choosing pull up/down resistor values. 1) like you have mentioned, the bus have more than 200mV (or 250mV depending how much margin you want to leave) DC voltage between A and B; 2) the equivalent resistance of termination RT and pull up/down is close to the cable impedance. You can refer to this blog for an example of the calculation. Please let me know if you have more questions.

Regards,

Hao

0 K.Hamamoto over 5 years ago in reply to Hao L

Guru 12155 points

Hi Hao,

Thank you for your prompt reply.

I understand. However we don't need the external circuit so that For this device the failsafe circuit is built-in. Is that correct?

Or do we need the external circuit just to be sure?

Best Regards,
Koji Hamamoto

0 Hao L over 5 years ago in reply to K.Hamamoto

TI__Mastermind 25705 points

Koji,

Yes, SN65HVD3082E has internal failsafe circuitry in the receiver, which makes the output keep high during failsafe conditions (idle, open, short). Please let me know if you have more questions.

Regards,

Hao

0 K.Hamamoto over 5 years ago in reply to Hao L

Guru 12155 points

Hi Hao,

Thank you !

Best Regards,
Koji Hamamoto

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SN65HVD3082E: Bias resistor for the external fail-safe circuit