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TXS0108E: issue check

Shu-Cheng LIN
Guru 11785 points
Part Number: TXS0108E

Hi Sirs,

Sorry to bother you.

As title, we found TXS0108E have wrong phenomenon on A4 pin.

Schematic:

If we disconnect all input /output, 

A4 pin as below

VCCA = VCCB = OE = 3.3V, we could found I2C CLK had 12.54MHZ waveform, after disconnect OE level the waveform is gone (The OE have original pull down resistor).

VCCA = 1.8V,  VCCB = OE = 3.3V, we could found I2C CLK had 8.8MHZ waveform, after disconnect OE level the waveform is gone (The OE have original pull down resistor). 

A4 pin as below

 Actually the CLK will connect with our light sensor, if it's always send these waveform that will effect our light sensor and EC communication.

We check our impedance/ x-ray, we don't saw any different between good and fail units.

The fail rate around 40/2600=1.5%

So, this waveform is normal? Could you help us explain it?

Thanks!!

  • 0
    TI__Guru 58600 points
    Hi Shu-Cheng Lin,

    I trying to understand the issue here.
    I see that the A4 pin is actually the A6 pin of the device which is I2C Clk, correct?
    Is disconnecting OE level and waveform gone an issue?
    Are there missing pulses in the 1.8V level which causes the freq to come down from 12Mhz to 8Mhz? I do not see an input freq on the scope shot.
    why is the SCL clock at such high speeds? For open drain signaling, the data rate is guaranteed up to 2Mbps.
    Also, OE pin is referenced to Vcca supply. Please connect OE to Vcca and not Vccb.
  • 0 in reply to ShreyasRao
    Guru 11785 points

    Hi ShreyasRao,

    My reply as below.

    I trying to understand the issue here. 

    Thanks!!


    I see that the A4 pin is actually the A6 pin of the device which is I2C Clk, correct? 

    a4 pin is IC pinout, A6 is for IC A side number six channel.


    Is disconnecting OE level and waveform gone an issue? 

    No, The issue is why we don't connected input/output, but still have a waveform (12.54M/8.8M) in Pin A4?

    Removed OE pin, the waveform will gone.


    Are there missing pulses in the 1.8V level which causes the freq to come down from 12Mhz to 8Mhz? I do not see an input freq on the scope shot.

    No any clock input, we just connect VCCA/B and OE. Only touch Pin A4 then we saw the 12.54M/6.6M waveform.


    why is the SCL clock at such high speeds? For open drain signaling, the data rate is guaranteed up to 2Mbps.

    We know, but we don't know where the CLK from, because we don't connected anything.

    Also, OE pin is referenced to Vcca supply. Please connect OE to Vcca and not Vccb.

    Understand, just for test not for final design.

  • 0 in reply to Shu-Cheng LIN
    TI__Guru 58600 points
    Hi Shu-Cheng,

    Thanks for the explanation provided.
    Now, I understand the issue that there is Clk signal being measured on A6 channel of the device even without any connection on the B6 channel of the device.
    What other channels are being connected and have signals on them? Even with crosstalk, there should not be any signal on unconnected channels when there is no active signal input on the other corresponding channel. Please disconnect all the channel signals while measuring again.
    When measuring the channel, is the scope ground probe connected to gnd or left floating?
    I havent come across this issue before where the signal is reaching the Vcca / Vccb levels.
  • 0 in reply to ShreyasRao
    TI__Guru 58600 points
    I will close this for now and if you have any more inputs, the thread will open up automatically.