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PCA9548A: back-powering via PullUp PCA9548A

Timo Reinhardt
Prodigy 10 points

Part Number: PCA9548A
Other Parts Discussed in Thread: TCA9548A

Hi,

I got a test setup which utilize a PCA9548A to control 8x DUT (on a test socket). The supply for DUT (VCC) is switchable.
Once I tun off VCC and unselect all channel, I still got a small voltage coming via the PullUps, as PCA9548A (in my understanding) is pulling those lines up in idle/unselect situation. This is preventing my DUT so safely beeing unpowered.

Question: is there a chance to unselect all channels and keep the outputs to Low, so as a result VCC will be 0V as well?

 

Screenshot 2026-08-26 090033.png

  • 0
    Guru 326790 points

    The pins of all unselected channels are high impedance. Are you actually measuring a voltage?

  • 0
    TI__Genius 11670 points

    Hi Timo,

    When the PCA9548A  is off the channels will be in a high impedance state (Meaning that the switch should be open and a signal should not pass through). Where are you measuring the voltage?

    Thank you,
    Arya

  • 0
    Prodigy 10 points

    seems my finding was caused by a completely different reason, as I put pull-ups on SCL/SDA (Pin 22/23) to VCC=3.3 and not to 5V. Note, the drawing above is not correct in respect the VCC Pin 24 is actually connected to 5V not 3.3V (5V for TCA9548A and 3.3V for DUT is correct). Since I changed, it seems to work so thanks for your input! Most important was also the confirmation, the outputs are High-Z once unused.