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UCD9248: Some questions about UCD9248

Minqiu Xie
Mastermind 21565 points
Part Number: UCD9248

Hi team:

There are some doubts about UCD9248.

1) UCD9248 has DPWM outputs. Is DPWM-1A necessarily the same as DPWM-1B? Are their phases related? Does DPWM-1A and DPWM-2A have independent frequencies?

2) Datasheet Page 12 “The UCD9248 contains four fusion power peripherals (FPP). Each FPP can be configured to regulate up to four DC/DC converter outputs.” This sentence means that the UCD9248 has 4 control channels. Each control channel can carry up to 4 power stages. For example, DPWM-1A and DPWM-1B are the output of one control channel, each with two power stages, for a total of four.
I guess my understanding is wrong. Can you draw a sketch to show me the exact meaning of this sentence?



3) Page 12:"The UCD9248 can control up to four rails, each of which can comprise a programmable number of power stages."
My understanding is that each power channel can be made up of several power stages. For example, in Figure 4 on page 9, the first rail has eight power stages. Is this understanding correct?

Thank you

  • 0
    TI__Genius 13700 points

    There are four Fusion Digital Power Peripherals in the UCD9248, each FPP controls two phases, A and B, and each phase supports a single Power Stage.  Since both phases are controlled by the same error signal they will both have the same switching frequency and duty cycle, the B phase will be 180 degrees out of phase with the A output.  The A and B phases of each FPP must be used by the same rail, they cannot be split between rails.  The B phase can be left Unassigned to allow for rails with odd numbers of phases (1,3,5,7).  See Fig. 4 of the datasheet which shows a single Power Stage for each phase output.

    Each FPP has access to its own PWM outputs and to the PWM outputs of the FPPs above it depending on the configuration.

    From Fig. 2 of the datasheet, FPP1 can be seen to have access to the A and B phases generated by its Digital High Res PWM and also the Digital High Res PWMs of the other three FPPs. Therefore, Rail number 1 could be configured to use FPP1 to operate anywhere from a single phase rail or up to 8 phase rail.  (FPP2 in the drawing was missing access to the Digital High Res PWMs of the upper peripherals which I have included in green).

    While FPP2 can be seen to have access to its PWM outputs and the outputs of FPP3 and FPP4.

    FPP3 has access to its PWM outputs and FPP4

    And FPP4 only has access to its own PWM outputs.

    Multiphase rails will have all its phases running at the same frequency and the phases will be spaced evenly across the rails switching period by default.

    Each rail can have its own separate switching frequency but I find it best to make all the rails operate at a single frequency (or at least multiples of the same frequency).

     

    The Fusion Digital Power Designer (FDPD) controls how the phases are split between the FPP sections and should not allow an invalid configuration, see below examples.

    First I attempted to create an invalid configuration with 2 three phase rails and a dual phase rail, but I tried to split the A and B phases of FPP2. As you can see the GUI has flagged the error and will not let me proceed.  It is not possible to create 2 three phase rails and a single dual phase rail even though there are eight phases on the UCD9248.

    Below I have changed the rail/phase configuration to a valid phase breakdown of a single three phase rail and two dual phase rails, only then will the GUI allow me to move forward.  Here Phase 2B has been Unassigned because the 2A phase was used for Rail#1.  Notice that the GUI provides information on how to connect the rails to the FPP error amps on the right hand side of the window, this will depend on the rail/phase breakdown as well.

    This is one example, the UCD9248 can be configured in a number of rail/phase combinations:

    4 - single/dual phase rails (single/dual relates to A/B phases of each FPP, a single phase rail assigned to an A phase will result in the B phase for that FPP to be unassigned)

    2 - three/four phase rails

    1 - three/four phase rail and 2 - single/dual phase rails

    1 - five/six phase rail and 1 - single/dual phase rail

    1 - seven/eight phase rail