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SN74GTL2010: can't pull down to 0V

Jen Hong Larn
Prodigy 20 points
Part Number: SN74GTL2010

Hi 

our application is 1.8V(FPGA) to 3.3V SPI flash, as below..

On U6 Pin 17 (SPI_DI),,,  It can't pull down to 0V ( about 1.1V) so it can't control SPI flash normally.

Can you tell me how to solve this issue ? thanks a lot

  • 0
    TI__Guru 55970 points
    hi Jen,

    what is the input voltage at pin8 ?
    It seems that the SPI driver is not able to sink all the current generated by the pull up resistor.
    you might have to increase the pullup resistance to 10k(may be on all ports).
  • 0 in reply to ShreyasRao
    Prodigy 20 points

    Hi Shreyas,

    Do you mean increase pull up register on S or D side  to 10k?

    My application :

    SPI frequency about  20MHz.

    the signal driver direction as below. those are my test record

    1. all pull up register=4.7K...   U6  pin 8 always 1.8V.( U8 can't pull it to 0V)

    2. all pull up register=180...    U6  pin 8 ,  U8 can pull it to 1.1V , can't pull to 0V)

  • 0 in reply to Jen Hong Larn
    TI__Guru 55970 points
    Jen ,

    what is the second condition ? is it 180ohm pull up resistor at U6 and U8 can pull down to 1.1V? the GTL is passive translator and the current generated through the pullup resistor has to be sunk by the driver which in this case is U8. Is U8 able to handle the sink current through all the channels and the low voltage can stay below Vol ?
    I would suggest trying 10k on both sides of S and D to see if U8 can stay low , disconnecting rest of the signals.