TRS3122E: sending signals all the time

Please show the schematic.

Hello,

A schematic would be helpful for us to continue with more detailed support. 

Regards,

Ethan

Thank you for sending that.

The FORCEON and FORCEOFF pins must be connected. If you simply want the device to be always on, please keep both pins high. Page 14 and 15 on the datasheet further detail these pins. 

Additionally the VCC pin and VL pins need to be directly connected to the 5V source. The capacitor must be tied to ground, not in series with the pins. 

Aside from those issues, the schematic looks ok. 

Best,

Ethan

Hello Ethan,

Thank you for your answer. But unfortunately this solution doesn't solve my problem. There is still a signal without sending signals from device.

Regards

What exactly do you mean with "signal"? A negative voltage, or changing voltages?

On the RS-232 bus, the only two valid states are less than −3 V and more than 3 V. For an UART, the idle state is negative. (This corresponds to the high logic state at DIN.) Also note that the DIN pins always must have a valid logic voltage (low or high).

You can disable the outputs by enabling some power-saving mode. In that case, the bus line will be pulled to GND by the pull-down resistor in the receiver (if there is one connected).

Please expand on what you mean by "signal without sending signals." When the TRS3122 is operational and transmitting, is the signal transmitting properly on the outputs still?

Clemens also makes a good point about the DIN pins. These should never be floating. Considering adding a pull-down resistor for these if you think these have chance of being undefined or floating. 

Another idea is that the ISO6742 is in a default high state, which might explain why you have a signal without transmitting on the TRS3122. 

However, I am not qualified on the isolation product line. If you have more isolation related questions, I can add them to this thread.