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SN74AVC8T245-Q1:

Wayne Liu
Expert 8605 points
Part Number: SN74AVC8T245-Q1
Other Parts Discussed in Thread: SN74AXC8T245-Q1
Hi,
If VCCA ramps up first, whether this power supply goes through to VCCB and port B3? On the other hand, if VCCB ramps up first,  and there are pull up on B port, whether  this power supply goes through to VCCA?
Thanks.
  • 0
    TI__Expert 8605 points

    Both ports have pull up resistors. 

  • 0 in reply to Wayne Liu
    TI__Expert 8605 points

    Datasheet writes:

    The output-enable (OE) input circuit is designed so that it is supplied by VCCA; when the OE input is high, all outputs are placed in the high-impedance state. To ensure the high-impedance state of the outputs during power up or power down, the OE input pin must be tied to VCCA through a pullup resistor and must not be enabled until VCCA and VCCB are fully ramped and stable. The minimum value of the pullup resistor to VCCA is determined by the current-sinking capability of the driver.

    It is a little bit confused, so I'd confirm with you, if I don't need high Z state, OE can be pull to GND, right? Thanks. 

  • 0 in reply to Wayne Liu
    TI__Mastermind 42640 points

    Hey Wayne,

    I'd recommend using the SN74AXC8T245-Q1 here. It will have more robust power sequencing. The device can be left enabled with no issues. Also, ramping up VCCA before VCCB wont mean that the voltage will show up on the B port I/Os.