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SN75HVD3082E dying due to voltage peaks on Data signal.

Michael Pfab4
Prodigy 50 points
Other Parts Discussed in Thread: SN75HVD3082E, SN65HVD1781, SN65HVD1780

Hello,

I have the following application:

I try to send RS485 data signal together with 48V/1A supply Voltage over two wires.

The data signal is electricaly isolated via 680µH inductors and 10µ capacitors.

My Data transceiver modules are connected together in a daisy chan. In every transceiver modul is a relay which can switch the Data/Voltage signal path on and off.

Due to the switching there are spikes at the Data signal (after the capacitors) with about 20V high and 50µs long.

I allredy have varistors (5V) at every data signal against GND and between them.

Stil some SN75HVD3082E are dying after some switching cycles.

Are there RS485 transceiver which a more tough against spikes or can someone recommend external components to protect the transceiver aginst them which are not disturbing the RS485 signal.

Thanks, best regards.

Michael

  • 0
    TI__Guru 62910 points
    Hi Michael,

    Using external transient voltage suppressor (TVS) diodes to clamp the input voltage to the RS-485 transceiver is a common way to protect these circuits. You would just need to choose a diode that could withstand the pulse expected and clamp the bus inputs to within their specified absolute maximum voltage range (-9 V to 14 V). Another solution would be to upgrade to a transceiver that is able to withstand these voltages. You may want to look into SN65HVD1780 or SN65HVD1781 (depending on operating rate needed) - these devices can withstand DC voltages up to 70 V on the bus pins, so the 20 V / 50 us pulse should be no problem.

    I hope this helps! Please let me know if you have any other questions.

    Regards,
    Max