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SN65HVD179: Shorting pin 7

Alpha H
Genius 10855 points
Part Number: SN65HVD179

Hi team,

I was wondering how the SN65HVD179 would respond if pin 8 (A) was shorted to 28V. Specifically, how would pin 7 (B) of the device behave, if the pin was left floating? 

The diagram on page 8 shows a detailed schematic of inputs A/B. It doesn't look like pin 7 would react to changes on pin 8, but I wanted to double check.

Thank you,

Arthur Huang

  • 0
    TI__Guru 62920 points
    Hi Arthur,

    You're right that in general the A and B pins are somewhat independent and voltages on one shouldn't couple through to the other. In the case of a 28-V short-circuit, though, damage to the device would be likely (given that the absolute maximum voltage supported on the A or B pins is just 14 V). When a device is damaged in this way, the effects can be difficult to predict with total certainty - high currents can cause damage to the metal/silicon structures of the chip and create short-circuits where none existed before. This means that a stress on the A pin could cause effects on B (such as a short circuit or additional leakage path to ground, to the A line, to VCC, etc.).

    If these kinds of short-circuits are expected in your application, you may want to consider an RS-485 transceiver with wider voltage tolerances on the A/B lines such as SN65HVD1791.

    Regards,
    Max
  • 0 in reply to Miguel Robertson
    TI__Genius 10855 points
    Thanks for the reply Max!