TCA9803: step voltage in SDAB/SCLB falling edge

Part Number: TCA9803

Hi, team,

I have one question about TCA9803 may need your help.

Customer's application is like below. Master is NXP LS1046A CPU, Slave is EEPROM.

In testing, we found there is a 700~800mV/100ns voltage step in SDAB and SCLB falling edge as shown below. Is it caused by the device internal current source?



2 Replies

  • Hi Johnny,

    This is strange. My initial thoughts is it could be the Master's FET not turning on fully for the initial 100ns. If this partially on impedance ended up being 200-Ohms, the current source could drive this voltage.

    How often is this occurring? Do all of your boards exhibit this behavior or just a few?
    To help narrow down the possibilities, you could try replacing the TCA9803 with a TCA9517 (with the B side towards the Master so the SVO won't interfere) and add pullup resistors to the B side. If the step still appears, its more likely a result of the current source.

  • In reply to Eric Schott48:

    The step is not narrowd when  i  changed the end up resister to 200 ohms ,but after I have replaced the TCA9803 with a PCA9617 ,there is not step on the falling edge.The waveform is below.

    PCA9617/SCLB/falling edge

    PCA9617/SCLB/rising edge