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PCA9548A: Device behavior after lock up

Johnny Guo
Expert 4910 points
Part Number: PCA9548A
Other Parts Discussed in Thread: TCA9548A

Hi, team,

I have questions about PCA9548A.

In datasheet, it is described as below

"If ramp conditions are outside timing allowances above , POR condition can be missed, causing the device to lock up."

1. Does it mean if Trise is too large, device will not be PORed?

2. What is the behavior after lock up? No output with high impedance?

Thanks.

Johnny

  • 0
    TI__Guru 72751 points
    Hey Johnny,

    "1. Does it mean if Trise is too large, device will not be PORed?"
    The device during normal conditions would start up with all the channels disabled. If you violate the POR requirements then I suspect the device may start up with random channels enabled. Some starts up could produce all channels on while others could produce one or two channels enabled, which would be random each time you violate the POR requirements.

    "2. What is the behavior after lock up? No output with high impedance?"
    When you say after lockup are you saying you reset the device again but your follow the PoR requirements? If so, the device will function normally again.

    The lock up condition is referring to the case where the device could potentially lock up SDA. This could be fixed by sending 9x or 18x SCL pulses to reset the state machine (I would say this should work most of the time).

    We do have the TCA9548A which fixes the PoR errata, is pin to pin with the PCA, is 5V tolerant, has a wider Vcc operating range, and is more cost competitive than the PCA9548A. I would recommend you use our TCA rather than PCA.

    Thanks,
    -Bobby