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TXB0104-Q1: Can't realize B->A transfer

Cera Wei
Intellectual 2010 points
Part Number: TXB0104-Q1
Other Parts Discussed in Thread: TDA2, TDA2E, TXB0104

Hi Team

My customer is now using our TXB0104-Q1. It works from A ports to B ports, but it doesn't work when using B ports to A ports.

B ports are from VP (TDA2) GPIO, and A port goes to DS90UB953 GPIO. The level of B ports are 3.3V, but when connected to B ports, the voltage changes to 0.5V. We tried several things:

1. Disconnect B ports with VP GPIO, the output of VP GPIO is 3.3V. When connected GPIO to B ports, the voltage changes to 0.5V

2. Disconnect A ports with 953 GPIO, which means leaving A ports floating, it's still 0.5V

3. When set 953 GPIO (1.8V) to output, we can get 3.3V output on B ports

4. All ports (A1-3 & B1-3) have the same phenomenon, we changed the chip, it still doesn't work.

5. 3.3V and 1.8V VDD1 power supply is good. 

Could you help look into this?

Thanks,

Cera

  • 0
    TI__Intellectual 2010 points
    Hello,

    We also tried to short connect 3.3V to B ports, it works. We tried to use a 10kohm pull-up resistor at port B, the voltage is only 1.3V.

    Thanks
    Cera
  • 0 in reply to Cera Wei
    TI__Guru* 97046 points
    Hi Cera,
    Based on the limited data you gave me, it sounds like the device "vp" has weak output drivers.

    To switch the line 'high,' the Bx pins must be forced 'high' by the driver at "vp", but it sounds like it can only get the voltage up to 0.5V . This allows me to calculate the output impedance of the device as 22.4 kohms.

    They need a driver with at most 1.7kohm output impedance. Can you provide any details on what the 'vp' device is?
  • 0 in reply to Emrys Maier
    TI__Intellectual 2010 points
    Hi Emrys,

    Thanks for your timely help.

    VP is our TDA2E, a processor for ADAS application.
    How did you get the 22.4kohm? I don't think the impedance is so large. Because if we pull up to 3.3V using a 10kohm resistor, the output is 3.3V. Only when we connect that to TXB0104, it turns to 1.3V.

    Thanks,
    Cera
  • 0 in reply to Cera Wei
    TI__Guru* 97046 points
    Hi Cera,
    Try pulling down with a 10kohm. The architecture of the TXB device includes a 4kohm series output resistor, which can act like a pull-up or a pull-down resistor depending on which state the output is in.

    I calculated the output impedance from the voltage you provided and the known output impedance of the TXB, which produces a voltage divider with the processor. Since the line never goes high, I can assume that something is holding the line low, and the only thing there is the TXB (as far as I know).