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Original question:

TXU0304: txu0104

TXU0104: VCCB increase as data transmission

Yolanda Guan
Prodigy 30 points
Part Number: TXU0104
Other Parts Discussed in Thread: TXU0304,

I notice that the VCCB voltage level increases from 1.2V to 1.6V as I have data transmission to the level shifter

I wonder if is it related to the NC connection at Pin 5?

Thanks, 

  • 0
    TI__Mastermind 26790 points

    Hi Yolanda,

    NC have no electrical significance to the device. Hence, unrelated and most likely correlated to the input signals. I would recommend observing how different factors from the input and output impacts the voltage level i.e. reducing frequency, reducing l or removing load, as well as how stable the power supply is, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 30 points

    Thanks, Michael. There is no load when we find this issue. Signals are GPIOs so not in high freq. Power sources are directly from DMM. We have another part TXU0304 using onboard seems working fine once we disable this TXU0104 part. Is there anything else we could check / try.

  • 0 in reply to Yolanda Guan
    TI__Mastermind 26790 points

    Hi Yolanda,

    Could you help confirm the power supply itself was 1.2 V? Please also help confirm the increase is only when data I/Os transmit the signals by helping to clarify the setup differences between the TXU0304 and TXU0104 setup as they both share similar design. Hence, less likely a TXU issue, thanks.

    Best Regards,

    Michael.

  • 0 in reply to Michael Ikwuyum
    Prodigy 30 points

    Hi Mike, 

    Yes the power itself is 1.2V, coming directly from a Keysight bench power supply. The voltage level stays until we initial the data transmission.

    Correct, the setup difference is just related to data transmission. 

    We find the following after initial the data transmission:

    1) disable TXU0304 and leave TXU0104 on, then initial the data transmission --> VCCB changes from 1.2V to unexpected 1.6V

    2) disable TXU0104 and leave TXU0304 on, then initial the data transmission --> VCCB stays at 1.2V

    Below is our design and the only difference between TXU0304 /TXU0104 is the Vin channel #. That is the reason I was trying to confirm with you on the NC performance. 

    Thanks, 

  • 0 in reply to Yolanda Guan
    Guru 263860 points

    Where exactly are you measuring the 1.6 V? At the VCCB pin, or at the B outputs? (In the latter case, please show an oscilloscope trace.)

    Why are you mentioning that you disable one chip? Are they somehow connected to each other? Are the NC pins connected to anything?

    (TXU inputs have internal pull-downs; leaving them open is fine.)