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SN65LVDS047: One driver in the quad driver package not working

Trevor Nielsen
Prodigy 20 points
Part Number: SN65LVDS047
Other Parts Discussed in Thread: SN65LVDS048A,

I am using the SN65LVDS047PWR to convert single-ended SPI signals to differential signals that can be sent along on cat5e cable. Each differential output is terminated with a 100-ohm resistor at the end, before being input into an SN65LVDS048A quad LVDS receiver. When I input a test clock signal (about 10kHz) into the inputs of the first and second drivers on the chip I get the expected differential outputs. When I input that same test clock into the third driver the differential outputs are fixed at roughly +2.6V relative to chip ground. The outputs do not change no matter what the input to the third driver is. I am powering the chip with +3.3V, and the input clock swings from 0-3.3V.

I have tried replacing the chip in the circuit, thinking that it might have been damaged by ESD or heat from soldering (even though it was reflowed with the correct profile) but the behavior of the third driver was unchanged between different chips.

Any help in diagnosing this would be greatly appreciated.


P.S. There seems to be an error in the SN65LVDS047 datasheet on the first page in the functional block diagram. The output of the AND gate shouldn't be tied to the input of the fourth driver, it should be tied to the enable line of the third driver.

  • 0
    TI__Mastermind 35130 points

    Hi Trevor,

    Just to clarify, each line on the output of the 3rd LVDS driver is fixed at ~2.6V, and this doesn't change if you swap units out? That's very strange. Have you checked if your board (or anywhere on this data path) has any shorts to power on these lines?

    Regards,

    I.K.  

  • 0 in reply to Ikechukwu Anyiam
    Prodigy 20 points

    Hi I.K.

    I figured out the issue, the footprint for the RJ45 jack I was using had the nets for the 3rd differential output swapped with another net, so I was not actually looking at the output of the 3rd driver when I thought I was. Once I probed the proper outputs the differential output showed up beautifully on the scope.

    I still think there's an error in the functional block diagram in the datasheet for the SN65LVDS047 though, the output of the enable AND gate shouldn't have a connection to the input of the 4th driver.

  • 0 in reply to Trevor Nielsen
    TI__Mastermind 35130 points

    Hi Trevor,

    Glad to see you resolved this issue. And yes there's an error in the functional block diagram. Thanks for pointing that out, I will work on getting that fixed in the datasheet.

    Regards,

    I.K.