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TLK1501 TTL Input Structure

Jeffrey McCasland
Prodigy 140 points
Other Parts Discussed in Thread: TLK1501

Could you please tell me if there are any protection diodes on the TTL inputs of the TLK1501?  I'm curious to know if two of these devices may have its TTL inputs connected in parallel with series resistors  allowing  for a cold spare application.  i.e. one device powered OFF with the other ON.  If so, do you have an application note or reference design indicating this?

Thanks!

Jeffrey

  • 0
    TI__Mastermind 20820 points

    HI Jeff,

    I am researching this with the IC designers. I will reply when I have a suitable answer.

    Regards,

    Mike

  • 0
    TI__Mastermind 20820 points

    Hi Jeff,

    There are protection diodes on the TTL inputs of the TLK1501. You could tie the TTL inputs together between the two devices but care needs to be taken in the design to ensure proper device operation. If device 1 has power and device 2 does not have power you will be driving 3.3V into the VDD node from the TD bus while VDD is essentially 0V. This will cause the diodes in device 2 to be fully on and the TTL node will be sitting at 1.4V with nothing to limit the current in that circuit but your driver.

    If both devices were to have power the Enable pin on the unused device could be pulled low which would keep VDD and the TD bus at a static level. Another approach that could be used would be to power both devices but only supply GTX_CLK to one of the devices at a time. Both of these techniques will protect the TLK1501 devices and keep your overall power consumption down.

    Regards,

    Mike