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TPS65251 Efficiency

Steve Hinshaw
Intellectual 515 points
Other Parts Discussed in Thread: TPS65251, TPS65251EVM

I purchased a TPS65251EVM eval board for verification of this part for a new design, but I’m not measuring efficiencies anywhere near what’s show in the TPS65251 datasheet.

For example, buck 3 of the EVM is setup for 3.3V output and the datasheet shows in fig 17 that the efficiency should be about 95% for output currents of 0.2 – 0.3A yet I measure efficiencies in the range of 87% to 91%.

Buck 1 is setup for 1.2V and fig 6 shows an efficiency of 88 – 90% for currents of 0.2 – 0.3A but I measure efficiencies of 71 – 76%.

How were the efficiency plots in the TPS65251 datasheet measured?

The eval board draws about 27mA @ 5V with all 3 switchers enabled but no loads, so how can this part provide the low-current (0.1 – 0.2A) efficiencies shown in the datasheet?

Is there a better part to look at for higher efficiencies for 3.3V, 2.5V and 1.2V outputs from 5V for output currents in the range of 0.2 – 0.4A?

Thanks,

Steve

  • 0
    TI__Guru**** 191445 points

    It is important to accurately measure VIN, VOUT, IIN and IOUT.  You will need to monitor VIN at the input capacitor VOUT directly at the point of regulation (where the FB trace is connected to Vout).  You can measure the currents with DMMs or using current shunts.  The published data should be accurate.

    You can get more info here:

    http://e2e.ti.com/blogs_/b/powerhouse/archive/2013/04/08/draft-blog-from-bob-hanrahan.aspx?keyMatch=measuring%20efficiency&tisearch=Search-EN

    and here:

    http://www.ti.com/lit/an/slva236/slva236.pdf?keyMatch=measuring%20efficiency&tisearch=Search-EN

    Let me know if you have additional questions.