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PCA9306: Power on sequence (VREF1 and VREF2)

K.Hamamoto
Guru 12155 points
Part Number: PCA9306

Hi

I read some E2E post as the following,

https://e2e.ti.com/support/interface/i2c/f/390/p/420667/1498896#1498896

However I do not understand which one of VREF1 and VREF2 should we startup first. 

In our customer case, 3.3V (this should be VREF2) power on first, then after 10ms the 1.8V(this should be VREF1) start up.

Because the 1.8V is provided from 3.3V rail by DCDC.

Should we start up VREF1 first anyway?

Regards,

Koji Hamamoto

  • 0
    Guru 12155 points
    Hi

    Could you support for this post?

    Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Intellectual 840 points
    Hi Koji,



    It is our recommendation that you start up Vref1 before Vref2, but there is no power sequence requirement for this part. That being said, no damage will occur to the device if you power it up the other way. If you power up Vref2 first you may see the low level on the Vref1 side propagate through to the Vref2 side. If your system can not handle this then you may want to implement the NMos solution in the post you linked.

    Here is another post on this topic that may help also:
    e2e.ti.com/.../1563337


    Regards,
    Daniel Noel
  • 0 in reply to Daniel R Noel
    TI__Genius 17245 points
    Hello Koji,
    Please do NOT implement the NMOS solution in the previous post. That circuit will not work. I will correct the post later.

    As long as you don't try to do I2C communications during the startup sequence than you should be fine either way that you power sequence.
    -Francis Houde
  • 0 in reply to fhoude
    Guru 12155 points
    Hi Daniel-san,Francis-san,

    Thank you for your support.

    I understood there is no any sequence between VREF and VREF2.

    Please correct me if my understanding is not correct.

    Regards,
    Koji Hamamoto