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TXS0108E: About external pull up resistor for TXS0108E

Andrew Xiong
Expert 4630 points
Part Number: TXS0108E

Hi team,

I have two questions about using a small external pull up resistor for TXS0108E.

1. Are there any other disadvantages except for increasing current into integrated MOS and increasing VOL?

2. For the method of calculating the required current sinking ability of the driver in application note SCEA054A: I=VccA/RA+VccB/RB (equation 1). RA and RB are the resistance of external pull up resistor and internal pull-up resistor. Why is VccA mentioned here since the external resistor is pulled up to VccB in the Figure2? Or the VccA is just a symbol which indicates the voltage source connecting with pull up resistor RA?

Thank you very much.

Regards,

Andrew

  • 0
    TI__Mastermind 42640 points

    Hey Andrew,

    The only disadvantage is the DC offset it creates. All of the pull-ups will have to be accounted for and as the app note states the RA and RB values are the equivalent parallel resistance of the internal pull-up and external pull-ups with the assumption they are using the same supply.