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TPS51222: Combine two outputs to one single output with larger current

inwave
Prodigy 10 points
Part Number: TPS51222
Other Parts Discussed in Thread: LM2642, TPS51220

I note that the TPS51222 has two outputs with 180 degrees of phase difference. I wonder if we can combine the two outputs together to generate a larger current output. I failed to find the description in the datasheet.

By the way, I am using LM2642 which can combine two outputs together to generate a single output with larger current. I want to evalute TPS51222 which has smaller footprint.

Regards,

Frank

  • 0
    TI__Guru 50515 points

     

    Since the TPS51222 uses fixed frequency, edge synchronized peak current mode control, it can, in theory, be used to generate a 2-phase converter like this by feeding the resistor divider feedback into both FB pins and connecting both COMP pins to the same C-RC compensation network.

    Since the channel 1 to channel 2 mismatch for both COMP to sensed current and FB reference voltages are not trimmed or characterized, we do not guarantee channel to channel mismatch (typically called current share) between the two phases when used in this configuration.

    If the converters are not run in Auto-skip mode, there is a risk that at light load currents, one phase will sink current from the output and boost it back to the input, creating a steady state cyclical current in the power stage, even under no load.

    If the converters are run in Auto-skip mode, it is likely that only 1 device will be switching while the other device remains in a high-Z state for an extended period of time.  Depending on the output voltage, this could affect the charge on the BOOT to SW capacitor when the load current increases and current is demanded from both phases.

  • 0 in reply to Peter James Miller
    Prodigy 10 points

    Any reference design or evaluation board design files for tps51222?

  • 0 in reply to inwave
    TI__Expert 7500 points

    Hi Inwave,

    As Peter said, it can, in theory, be used to generate a 2-phase converter. But actually we don't recommend to use as 2-phase since there are channel to channel mismatch and what's more, we don't have such reference design.

    Thanks,

    Lishuang

  • 0 in reply to inwave
    TI__Guru 50515 points

     

    I do not see an active evaluation board, or design files for one.

    If we have a reference design, it will not be fore a 2-phase, single output design, but two separate outputs.

  • 0 in reply to inwave
    TI__Guru 50515 points

     

    We do not have a TPS51222 reference design, however the TPS51220 is very similar, with a similar pin-out.  You can evaluate the TPS51222 on the TPS51220 evaluation board with some modifications.

    In addition to switching out the controller ICs, the TPS51222 replaces the FUNC (Function) pin of the TPS51220 with the IMON1 pin, and the TRIP pin with the IMON2 pin.

    For the TRIP to IMON2 pin, you'll want to remove R38 (zero-ohm resistor) and populate R27 / C31 for the IMON2 output R-C filter.

    For the FUNC to IMON1 pin, you'll want to remove R39 (zero-ohm resistor) and populate R32 / C28 for the IMON 1 output R-C filter.

    This provides for a 5.0V @ 6A output on channel 1 and 3.3V @ 6A output on channel 2.