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TXS0108's low level output issue

Lee, Sam
Expert 6065 points

Hi team

Can you help solve the following issue?

In an application of 1.8V to 2.8V, TXS0108 has an issue that shows 700mV at low level. It seems that the problem is due to an external pull up resistor of 2kohm between TXS0108 and I2C I/O of touch panel IC. If the external 2kohm is removed and the internal pull up of TXS0108 is only used, the I2C line works. However, the touch panel company recommended the external pull up of 2kohm.

In this case, is it okay to remove the external pull up on this I2C line?

 

Thanks,

Sam Lee

  • 0
    TI__Mastermind 30835 points

    Hello Sam,

    The pull-up will affect the Vol level. A 2k may be too strong, we can use the equation below to find the minimum value of pull-up that we can use. 

    Rpu(min) >=  [Vcc-Vol(max)]/Iol(max)

    From the datasheet, if we assume that Iol = 400uA, Vccb = 2.8V, and Vol(max) = 0.55V we find that the minimum pull-up to be roughly 6k ohms. 

    If the touch panel seems to be operating fine without the external pull-up you can probably just use the internal pull-ups. The internal pull-up has a value of 4k. 

  • 0 in reply to aozer
    TI__Expert 6065 points
    Thanks Aozer.