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TCA9406: TCA9406DCU

AGXIN
Intellectual 510 points
Part Number: TCA9406
Other Parts Discussed in Thread: TMP102,

Hi 

I am using this Device for Level Translation in I2C bus 

The following is the schematic diagram attached 

3.3V is connected to MC and few of the devices (TMP102) and a I/O expander ,ALS chip SI1133

and 1.8V is connector to few image sensor IC 

when this out put pin is enabled and the I/O expander board not powered (disconnected ) we are facing some detection issue in an ALS chip

while debugging if we pull this line OE low their is still voltage available at both ends of the line 

as per the datasheet if the Line is pulled Low their should not be any voltage on both ends It should be floating 

but we are able to see some voltage always 

how can we avoid this we have disconnected pull ups at all the lines but still issue is consistent  

  • 0
    TI__Guru 62920 points
    Hi AGXIN,

    Just to clarify - do you mean that the 3.3-V supply on VCCB is disconnected (meaning that pin is connected to a high impedance but the 1.8-V supply is still present, and you are seeing some voltage on the I2C0_SCL (SCL_B) and I2C0_SDA (SDA_B) nets? What voltage are you observing? Does it change depending on whether or not you have pull-ups installed on the B-side SDA/SCL lines?

    Max
  • 0 in reply to Miguel Robertson
    Intellectual 510 points
    Hi
    no power is connected to VCC3V3 (open) the voltage we are seeing on the 3.3 side is varying between 0.5 to 3.3
  • 0 in reply to AGXIN
    TI__Guru 62920 points
    AGXIN,

    If VCC3V3 is floating and you confirm that the voltage at the VCCB pin is below 3.3 V, then the 3.3-V voltage you are measuring on the I2C lines would have to be coming from somewhere else. I'm still not sure I fully understand the application, though. Do the MCU and the IO expander also share this VCC3V3 rail? Does the MCU share a PCB with the TCA9406, and the IO expander is on a separate board? (If so, is that separate board completely disconnected or simply powered down?) At which locations are there pull-up resistors populated, and what are their values? If you could just describe everything that connects to the I2C lines during this test (or provide a more full schematic) it would be helpful.

    Also, are you observing this voltage with a voltmeter/DMM or an oscilloscope? Is the voltage fairly stable (you mentioned kind of a wide range), or does it vary a lot with time? Do you get different values using different measurement techniques? If so, it may be arising from a very high-impedance leakage path and so the loading of the meter/scope would influence the voltage level. (You could also check this by connecting a large resistance like 100 kOhm from the I2C lines to ground and seeing if this is sufficient to pull the voltage closer to 0 V.)

    Max