TS5A3166: GPIO controlled RS485 bus termination resistor

Bekir KÖR

Part Number: TS5A3166

Tool/software:

I am trying to design a circuit to control the RS485 bus 120 Ohm termination resistor using 3.3V GPIO from an STM32 MCU. I have never had such an application before.

My RS485 interface works with an isolated 5V supply. When I use TS5A3166DBVR, I think I can enable or disable the RS485 bus 120 Ohm termination resistor directly with GPIO.

Is there something I am missing in the application?

5 months ago

0 Clemens Ladisch 5 months ago

Guru 316440 points

The switch must support all voltages that happen on the bus.

What are the bus voltages that can actually happen in your application? Why are you using ±275 V TVS components?

0 Bekir KÖR 5 months ago in reply to Clemens Ladisch

Prodigy 80 points

Hi Clemens

The bus voltages that can actually occur are 5V. We use ±275 V TVS components for ESD protection and any external faulty connections.

+1 Clemens Ladisch 5 months ago in reply to Bekir KÖR

Guru 316440 points

If the bus voltages cannot be lower than 0 V or higher than 5 V (i.e., if there is no ground shift between the RD-485 nodes), then you can use a 5 V switch like the TS5A3166.

0 Bekir KÖR 5 months ago in reply to Clemens Ladisch

Prodigy 80 points

Thank you Clemens

One last question. I connected the trigger signal from the 3.3V GPIO pin of the MCU directly to pin 4 (IN) of the TS5A3166. Should I put a series resistor in between or is it fine as it is?

+1 Clemens Ladisch 5 months ago in reply to Bekir KÖR

Guru 316440 points

The control pin is a high-impedance input, so a resistor is not needed.

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TS5A3166: GPIO controlled RS485 bus termination resistor