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MCF8329A: Design not using AVDD

Makoto Oka
Prodigy 210 points
Part Number: MCF8329A

I have received question from customer. Can you please comment on this?

We are considering connecting to the external power supply IC 5V instead of using AVDD.
We think that 5V pullup is needed for the parts pulled up by AVDD (FG, nFAULT, SCL, SDA).
When AVDD is not used, we think that the AGND should be connected via 1uF. Is this correct action?

  • 0
    TI__Genius 13195 points

    Hi Makoto,

    Makoto Oka said:
    When AVDD is not used, we think that the AGND should be connected via 1uF. Is this correct action?

    This is correct. Even if AVDD is not used, a 1 uF capacitor rated for at least 6.3 V needs to be placed between AVDD and AGND and as close to the device as possible.

    Makoto Oka said:
    We think that 5V pullup is needed for the parts pulled up by AVDD (FG, nFAULT, SCL, SDA).

    This is correct. FG and nFAULT need to have pullups and we recommend using pull ups on SCL and SDA. This pull-up voltage can be supplied by an external power supply if AVDD is not used. For FG and nFAULT please keep in mind the note found in section 7.3 of the datasheet that these pins need to be pulled high prior to the MCF8329A entering active state.

    Regards,

    Joshua

  • 0 in reply to Joshua Horlander Cruz
    TI__Prodigy 210 points

    Thank you for the answer.

    What should they do for the AVDD pin? Floating? 

  • 0 in reply to Makoto Oka
    TI__Genius 13195 points

    Hi Makoto

    AVDD requires the 1uF cap between AVDD and GND even if not used. Other than the cap, no other connection is required if not used.

    Regards,

    Joshua