THVD1450: Pull-up voltages for D, R, DE and RE pin

Shunsuke-san,

THVD1450 has internal pull up resistors on D, REB pins and pull down on DE pin. R pin doesn't have any since it's output only.

I attach an app note about 3V MCU to 5V transceiver connection for your reference.

Please let me know if you have more questions.

Regards,

Hao

3000.3V MCU to 5V XCVR Interface.pdf

Hi, Hao -san,

The attached file is for the connection in RxD only. In this connection RE, DE and D connect to 5V through pull-up register. this mean is MCU O/P1, O/P2 and TxD may get 5V which is out of specification, and damaged.

Do you have alternative solution or device ?

Regards,
Nagata.

Hi, Hao -san,

If user add the pull-down register at system side to keep 3.3V for D, R, DE and RE pin. is it possilbe not to take damage to FPGA/MCU?
Could you please review my idea?

Btw, I'm interesting in the THVD1520, too. Does it have pull-up register?

Regards,
Nagata.

Shunsuke-san,

I guess adding external pull down resistor might work, which is equivalent to having a resistor divider in the input. One thing you may want to pay attention is that if the bias point of the input circuitry is close to middle, it might make both PMOS and NMOS on therefore generate a through current from Vcc to GND. In application, please keep an eye on the RS-485 power dissipation (disabled) by comparing it with the data sheet spec.

Talking about THVD1520, it also has similar internal pull up / pull down. The reason is that we want the transceiver to have a determined state when it's powered up. Please let me know if you have more questions.

Regards,
Hao

Hao -san,

Thank you for your support.

Could you please let me know min/max internal pull up register data?

Regards,

Nagata.