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AM26LV31E-EP transient supression

Newton
Expert 1125 points
Other Parts Discussed in Thread: AM26LV31E-EP, AM26LV31

For  AM26LV31E-EP line drivers, is it OK to put  a transient voltage suppression diode with a clamping voltage of +/- 13 volts at each conductor of the differential line?

We  need to be protected against Lightning as per RTCA/DO-160E Level XXK33.

 

AM26LV31E-EP is ESD protected upto +/- 15KV.

The  data sheet specs are : absolute maximum ratings in case of input/output is -0.5 Volts to +6 Volts.

 

 

 

regards

  • 0
    TI__Mastermind 28265 points

    Hello there,

    Yes it is okay to put a TVS on each conductor line. For long data lines you might actually connect TVS diodes to the driver as well as the receivers, if the nodes are far aprt.

    Be careful what TVS diode you choose as its capacitance will determine the maximum data rate you can apply.

    Another important parameter is the TVS clamping voltage. Lightning transients are usually long surges and require high power TVS (apprx. 1500W, sometimes even more).

    the clamping voltage can be in the 40V to 60V range. To protect the bus pins, in particluar the driver outputs, you might use 5 ohms to 10 ohms MELF resistor in series to each driver output.

    Would you are to tell me which TVS diode you have in mind?

    Best regards,

    Thomas

  • 0 in reply to Thomas Kugelstadt
    Expert 1125 points

    Thanks Thomas.

    Just to clarify:

    The data sheet says absolute maximum rating at input and output as -0.5 Volts and +6 Volts.  The device has protection against ESD of +/- 15 KV. We want to put a bipolar TVS diodes with a clamping voltage level of +/- 13 Volts on each of the conductor of the RS422 line. Will this violate the maximum limit specified by your data sheet if the lines are held at +/- 13 volts as and when a transient is received by the lines?  

    regards

  • 0 in reply to Newton
    TI__Mastermind 28265 points

    Most transients exceed the maximum specified voltage range. If this happens, internal ESD celles kick in and try to absorb the excess energy by internall bypassing the driver circuit. The AM26LV31 has quite robust ESD protection as you can already see from the data sheet front page. This however are only ESD transients which are very short in duration and small in energy content. Electrical fast transients (EFT or Burst transients), while similar in duration as ESD transients, have a significant higher power content. Finally Surge transients have the highest energy content as they are typically 1000 times longer in pulse duration.

    SEMTECH, Vijay, Protek Devices, all provide transient supressors for all three types of transients. When the transient occurs, the TVS starts clamping. This clamp voltage usually exceeds the maximum specified voltages in the data sheet. Then the device internal protection circuitry must be robust enough to survive the duration of the clamping voltage. A common approach to limit the clamping current into the driver output terminals is to add 5 ohm to 10 ohm MELF resistors in series. MELF therefore because of their low inductance.

    Note: the maximum specified voltage levels in the data sheet apply to constant voltage conditions such as DC. In the case of transients, much higher voltages can be survived . Again, how much depends on the internal protection circuitry.

    Best regards,   Thomas