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PCA9306: PCA9306: Question for Pull-high VCCx

GaryC
Expert 3585 points

Part Number: PCA9306

We use remote board insertion to main board as show in below. The remote board use internal 1.8V pull-high I2C, and the main board use 3.3V pull-high I2C. The enable of the PCA9306 is controlled by MCU GPIO. My question is how to decide the VCC2 and VCC1. For example, may I use the same 3.3V for VCC1 and VCC2 for this design? Or it should be 1.8V for VCC1, and 3.3V for VCC2. Or VCC1 can be shorted to ground, since the remote board use internal 1.8V pull-high I2C.

BR,

Gary

  • 0
    TI__Guru* 79531 points

    Hey Gary,

    Vref1 and Vref2 can technically be interchangable but then the GPIO note on the enable must not exceed the lower of the two voltage ranges plus Vth.

    Typically though, Vref2 is the higher side voltage rail and Vref1 is the lower side voltage rail.

    "may I use the same 3.3V for VCC1 and VCC2 for this design?"

    For THIS DESIGN, you can get away with doing this BUT the GPIO controlling the enable pin cannot exceed 1.8V+Vth. <-- this ensures that the level translation feature would still work.

    -Bobby

  • 0 in reply to BOBBY
    TI__Expert 3585 points

    Hi Bobby,

    Thanks for your help.

    May I check again about the "Put the same 3.3V for VCC1 and VCC2"?

    As refer to below, If the VCC1=VCC2, then the enable voltage from the GPIO of the high logic is not exceed Vref + Vth. For my application, If we use the same 3.3V at VCCx, then the enable voltage should not exceed 3.3V + Vth. Is that correct?

    One more question. May I know the Vref1 can be shorted to ground or leave open? Since the remote board will be internal pull high. 

    BR,

    Gary

  • 0 in reply to GaryC
    TI__Guru* 79531 points

    "As refer to below, If the VCC1=VCC2, then the enable voltage from the GPIO of the high logic is not exceed Vref + Vth. For my application, If we use the same 3.3V at VCCx, then the enable voltage should not exceed 3.3V + Vth. Is that correct?"

    Because in your system you are using a low translating voltage of 1.8V (even though your Vref is 3.3V) the new enable voltage rule is Venable cannot be larger than 1.8V+Vth.

    "May I know the Vref1 can be shorted to ground or leave open? Since the remote board will be internal pull high. "

    If you are using Figure 10 set up, it is possible for you to GND Vref1 and keep Vref2 as 3.3V.

     

    Also, before you push your design out for board fabrication. If you like, send me the schematic around PCA9306 at duynguyen@ti.com and I can take one last look to verify that the PCA9306 is correct.

    Thanks,

    -Bobby