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TPS55010 EVM measured efficiency does not match documentation

Jonathan Guy1
Prodigy 90 points
Other Parts Discussed in Thread: TPS55010EVM-009, TPS55010

Hi,

Before making modifications to the TPS55010EVM-009, I ran a set of bench tests to compare efficiency to the curve provided in the documentation.  The problem is I'm consistently seeing efficiency lower than expected - by a large margin.

Here are three data points from my data-set (all at 5V, with default switching frequency):

42mA output: Actual 56%, EVM Spec ~80%

112mA output: Actual 73%, EVM Spec ~87%

218mA output: Actual 77%, EVM Spec ~85%

My only other observation is that the duty cycle is varying less over the load range than I would have expected (from 54% to 58%).

Any ideas why EVM measured efficiency does not match the EVM documentation?

-- Jon

 

  • 0
    TI__Mastermind 35135 points

    Hi Jon,

    The duty cycle should not vary much over the load range because this is a synchronous converter allowing the low-side FET to sink current. The reason the duty cycle changes is mainly due to voltage drops across the FETs and primary winding of the transformer.

    As for the difference in efficiency measurements. One important thing to get accurate measurements is that the input voltage is measured near the DC/DC converter. Voltage drops across cables from a power supply can make it appear less efficient than it actually is. The same goes for measuring the output voltage.

    Can you share your raw data used to calculate the efficiency?

    Best Regards,
    Anthony 

  • 0 in reply to Anthony F
    Prodigy 90 points

     Anthony,

     

    Thanks for the input. The shunt in the Agilent 34401A was dropping a little more than I expected on the input stage in some ranges.  Unfortunately that just makes the data look worse.  I'm not too worried about the 10mA efficiency, but the other data points are a concern. I've crossed checked my meters, so I'm confident my measurements are accurate.

    TPS55010 Evaluation using TPS55010EVM-009

    Default board configuration

    Vin (V)

    Iin (mA)

    Pin (mW)

    Vout (V)

    Rload

    Iout (mA)

    Pout (mW)

    Efficiency %

    4.69

    67

    314.2

    5.22

    500

    10.4

    54.5

    17%

    4.94

    179

    884.3

    4.94

    44

    112.3

    554.6

    63%

    5.38

    280

    1506.4

    4.83

    22

    219.5

    1060.4

    70%

    Current measurements: Agilent 34401A

    Voltage measurements: Fluke 70 series

      -- Jon

  • 0 in reply to Jonathan Guy1
    TI__Mastermind 35135 points

    Thanks Jon.

    How come the Vin voltage varied so much across the load conditions? Is the Iout actually calculated based on Rload and Vout? It is best to measure the real current.

    My first thought is the switching frequency of this part is in the high range of the variation. Can you measure the switching frequency?

    Anthony