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TPS650864: Question about efficiency

Austin Do
Expert 3335 points
Part Number: TPS650864

Tool/software:

Hello team,

I have questions about efficiency.

1. How do you measure efficiency of Buck 1? Disabled other regulators?

2. In case of 3.3Vout, Why efficiency is low in light load compared to other cases? Also, why efficiency becomes better in high load?

Best Regards,

Austin

  • 0
    TI__Mastermind 22255 points

    Hi Austin,

    1) Efficiency should be measured with the other regulators disabled. You want to isolate the input current so that only BUCK1 power in and power out are considered.

    2) I'm checking internally with one of the old designers to see if he has any insight on the efficiency drop shown on that graph. I'm not sure how busy the team is so I'll let you know what they say when they get a chance to respond.

    Regards,

    James

  • +1 in reply to James Steenbock
    TI__Mastermind 22255 points

    Hi Austin,

    I'll relay what the old design team mentioned about the efficiency:

    "In PFM mode, when the output is very high and headroom is low, the inductor peak current is low and the current will return to 0A very fast (inductor current change slope in function of VOUT), the comparator detection may not be fast enough to detect zero current and shut down the LS FET in time. This resulted in negative inductor current. Negative current will discharge the output and causes additional power loss."

    So the efficiency behavior you are seeing appears to be a combination of the smaller difference between VIN and VOUT along with low load current.

    Regards,

    James