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TXS0108E-Q1: IO state

Chuqiang Wen
Expert 5825 points
Part Number: TXS0108E-Q1
Other Parts Discussed in Thread: TXS0108E

Hi Expert, 

Customer met some questions on TXS0108E-Q1 in their project. You can find the schematic as below.

In customer system, there have one case that PERIPH_1V8_SW(VCCA of TXS0108) power on later than cluSOC_VRTC_1V8 and cluSOC_VDD_1V8. Their expectation is all the Ax and Bx are under Hi-Z state before VCCA and VCCB completely power up. From the description in datasheet, we should pull down the OE pin. 

Customer modify the OE pin to GND, but found A1 pin is 0.4V before VCCA power up, it is not Hi-Z state. There have cluSOC_VRTC_1V8 pull up on A1, it should be 1.8V at Hi-Z state. You can find the waveform as below. CH3 is A1 pin, CH2  is VCCA. 

Can you help check? 

Thanks!

Ethan Wen

  • 0
    TI__Mastermind 40136 points

    Hey Ethan,

    The TXS0108E does not have the IOFF feature, so the I/Os will not be placed in high-Z if VCCA and/or VCCB is powered down. What is the state of VCCB during this time? 

    From the schematic, a value of >50kohms for the external pullups is recommended to not contend with the internal 10kohm pullups. Similarly, please remove the caps on the signal lines (C7301 and C7300) as the device performs best under 70pF lumped capacitive load.