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TCA9509: pull-up resistor on A side

Hailiang Zhang
Genius 11020 points
Part Number: TCA9509
Other Parts Discussed in Thread: TCA9617B

Tool/software:

Hi Expert，

My customer met an issue on TCA9509 application. From datasheet, port A should have internal current source so that don't need external pull-up to VCCA. But the vendor of the master review and feedback that it is recommend to add the pull-up resistors, and my customer do see on previous design have the pull-up on Port A. So I'd like to confirm that add pull up on Port A should be still workable or not. Is there any risk to add the resistors?

Regards,
Hailiang

  • 0
    TI__Mastermind 40136 points

    Hi Hailiang,

    Yes- external pullups should not be placed on A-side of this buffer due to the internal current source at this side. If the pullups are an absolute requirement, we can look at different buffers like the TCA9617B or the TCA9980x that allow pullups on A-side. 

    If the customer insist on using TCA9509 and the external pullups on A-side, please note that they must be large enough so that devices on A-side must be able to pull the lines below 0.11V. If your driver on A-side is strong enough to sink the current from external pullup and the internal 1mA source of the TCA9509 and maintain VIL into I2C buffer then this can work. 


    Regards,

    Jack