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Is PCA9539 Failsafe?

Nabeel Khan
Intellectual 1455 points
Other Parts Discussed in Thread: PCA9539, TCA9539

Hi Team,

Are the IOs on the PCA9539 failsafe, meaning when the device is powered off do the IOs have very low leakage (i.e. hi-z state)?

Thanks!

Nabeel

  • 0
    TI__Genius 16510 points
    Hello Nabeel,

    These devices do NOT have a guaranteed powered off state. We recommend that no voltages be applied to the devices IOS when unpowered.

    also, we recommend using the TCA9539 which is p2p with the PCA9539, but is newer and has a power on errata bug fixed and has lower voltage support.
  • 0 in reply to Jonathan Valdez
    TI__Intellectual 1455 points
    Would applying a voltage to IOs when the device is unpowered damage the part? If so, is there a current limit at which damage would occur? Let’s say we have a 4.7KΩ pull-up to 3.3V on the IO, is that ok since it’s current limited?
  • 0 in reply to Nabeel Khan
    TI__Genius 16510 points
    Hello Nabeel,

    The main concern is that any voltage applied to an IO when unpowered has the potential of back flowing through the IO pins and pulling the VCCP rail up. We have seen where this is enough to power the device.

    4.7k to a 3.3V IO will not damage the port, but does have the potential of pulling the VCC pin up if the power supply does not short to ground when turned off. You will want to have the customer check the operation of their power supply when it is disabled or powered off (short to ground or high-z)