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TCA9538: TCA9538

Part Number: TCA9538
Other Parts Discussed in Thread: TCA9406

Hi 

I am using a I2C LT which is connects processor I2C bus to TCA9538 PW I/O expander IC .Processor  12C side is 1.8V and TCA9538PW side is 3.3.The power to the IC TCA9538PW  is provided through a Switch .By default the I2C line is connected to the I/O ex pander(and pullup on this lines is also connected )  but power is not connected to the IC by default .The power pin of the IC is reading 0.4 V even if the power line is completely disconnected the 0.4V is appearing between power pin and GND pin of the IC 

 

  • AGXIN,

    Is there any way you can share a schematic or a portion of a schematic that would give a little more information as to where the rest of these voltage sources and signals are going? From what you've described it seems like a leakage path is happening somewhere. There's absolutely nothing on the VCC pin when the switch is open, correct?

    Regards,
  • Hi Eric 

    Thanks for the quick response 

    I am herewith attaching the schematics having the information about the devices connected to the bus 

    TI_ALS_I2C_BUS.zip

  • AGXIN,

    Leakage paths can be present on the voltage translator and Mux devices if the right conditions are present, I'm thinking the pullups on the I2C bus or on the Reset pin might be causing the 0.4V to show up on the VCC pin. Can the pull ups on these pins be removed and then checked to see if the 0.4V is present on VCC? Start with the Reset pin first, then if that doesn't change anything, move to the SCL and SDA pins and remove those pull ups as well.

    You mentioned in the previous post that VCC is provided through a switch, does that mean the "VCC_3V3" is provided to the rest of the board through that switch, or just to the TCA9538 device?

    Regards,

  • Hi Eric,

    Thanks for the reply

    Pullup on the bus is present internal to the processor and the power to the devices on the bus is provided through the switch

    for reset and address pin detection the switched power is used for pull up

    only I2C pull up will be enabled before the device is powered on

  • AGXIN,

    I just want to make sure I understand the system setup, the net names on the schematic are a bit confusing.

    So there is a Processor connected to the TCA9406 level translator, to feed into the TCA9538 IO expander. Is this correct? I ask because on the schematic I see the following:

    In the red circles are all the same net, which look like the net of the output of the processor. And then on the level translator I see two separate nets, neither of which go into the IO expander or the light sensor.

    And then to clarify your previous post, only the pulls on the processor side are connected internall (1.8V), the pull ups on the IO expander side of the translator are not connected unless the 3.3V switch is in the correct position. Is this understanding correct?

    It's clear there's a leakage path being created by something connected to the TCA9538, and the only pins that are supplied in this condition where 0.4V is seen on VCC, are SDA and SCL, correct?

    I know you'd rather see answers and not more questions from me, I just want to make sure I understand the connections when this voltage is present.

    Regards,