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PCA9306: Vref 1 Voltage leakage problem

Part Number: PCA9306

At Vref1 , 2.5V measured .  But this port is 1.8V.  I also viewed the simmilar issue at E2E. But I could not fine the correct answer.

I attatched my schematic.  There are 5 block for PCA9306.  At 1.8V point, 2.5V measured.  VREF2 and EN connected to 3.3V via R 220Kohm.

I've done a lot of reviews. But it did not work out.

I would appreciate it if you could tell us why this is happening.


  • Hi SungRok,

    There will be a small amount of leakage from Vref2 to Vref1. The Vref2 pull-up resistor helps to limit this, so you should be sure to double-check its value. Even with a large enough resistance on Vref2, though, it is possible to see a voltage increase on Vref1 if the power supply providing Vref1 is unable to sink current. In this case, a large pull-down resistor (for example, 270 kOhm) on Vref1 should help.

  • Hi Max.

    Thanks for your quick reply.
    I installed the 250kohm Resistor at each Vref1 position. As a result , Vref1 voltage measured 1.9xxVolt. Not 1.8Volt.
    But I 'm OK. This is fine.

    And If you know an I2C Level Shifter that does not have this problem, please recommend it.

    Anyway , Thanks for yoour support.

  • Hello SungRok,
    What else is on the 1.8V rail? Is there no other load on that supply rail? I can't read the image on the schematics, what is the part you are using for generating the 1.8V rail? If you have no load on the 1.8V it is possible it gets into a state that it floats up above 1.8V. You could consider a shunt voltage regulator. That means it can sink current to regulate to keep it at 1.8V. Do you have strict power requirements?

    Also, can you confirm if you have 470 Ohms as pull up resistor values on the SDA1/SCL1? If you are using 470 ohms that that looks like a strong pull-up, do you have a lot of capacitive loading? What frequency are you trying to communicate at? 100kHz, 400kHz???

    I would like to know more about the application, can you elaborate on what you trying to do? This seems like a unique application.
    -Francis Houde