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TCA9509: When disconnect the power supply separately

NAOKI AOYAMA
Guru 11215 points
Part Number: TCA9509


Hello,

Our customer use the TCA9509 with VCCA=1.8V, VCCB=5V.

When the customer disconnect the VCCA, a voltage remain 0.5V at VCCA, SCLA and SDAA pin.

What is the cause of this behavior?

Is that correct operation?

Of cause, there is no termination resistor at A side.

Best Regards,

Naoki Aoyama

  • 0
    TI__Guru* 77381 points
    Hello Naoki-San,

    Can you provide a schematic or block level diagram?

    "Is that correct operation?"
    This doesn't sound normal to me. Our device allows for the power sequencing to occur with either A or B turning on at different times. When VccA is below 0.8V the device should go into high impedance mode.

    The TCA9509 does have a current source on A side, I am wondering if you are somehow biasing an internal diode.

    How many boards do you see this one?
    Does this happen everytime you power down VccA?
    If you apply voltage back to VccA does the problem go away?
    Do you have scopeshots of VccA going low and SDA/SCL/VccA going to 0.5V?
    Is VccA being powered through a lab PSU or using an LDO?

    Thanks,
    -Bobby
  • 0 in reply to BOBBY
    Guru 11215 points
    Hello Bobby,

    Thank you for your reply.

    Sorry, but the customer evaluate it in more detail, the problem is solved.
    There is an MCU in front of the TCA9509. It operates by common power supply.
    It occurred caused by this MCU.

    Thanks,
    Naoki Aoyama