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Original question:

[FAQ] Common MCx Schematic and Layout Q/A

MCF8316A with external 3V3?

Neil
Prodigy 40 points
Other Parts Discussed in Thread: MCF8316A

Looking at the FAQ for the MCF8316A:

https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1236299/faq-common-mcx-schematic-and-layout-q-a

If I already have a 3V3 supply available, can I disable the buck as described, and connect AVDD and FB_BK to this external supply?

That way I am not dissipating any additional power in the device, other than switching the motor.

Thanks,

Neil

  • +1
    TI__Genius 9220 points

    Hi Neil,

    Connecting external 3V3 supply to AVDD and FB_BK is NOT recommended since one section of MCF8316A may be powered while another section will not powered (if external 3V3 is present while Vm is not). When the other section gets powered on, a full device reset would be needed to ensure there is no unexpected device behavior. So, TI does NOT recommend this configuration.

    Instead, TI recommends simply connecting AVDD to FB_BK, which essentially bypasses the buck regulator. In this configuration, VM sources -> AVDD LDO which sources -> DVDD LDO. (DVDD is generated from FB_BK voltage and used to power MCF8316A's digital circuit.) The downside of bypassing the buck regulator this way is that that the power loss from the internal AVDD and DVDD LDOs are dissipated in the IC instead of an external resistor when using buck regulator in resistor mode.

    Regards,
    Eric C.