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SN6501: Efficiency is significantly lower than specified in datasheet

Eelco Simonse
Prodigy 125 points
Part Number: SN6501
Other Parts Discussed in Thread: SN6505B

I have a product design with SN6501 transformer driver. I used the reference design specified in the datasheet, from 3V3 to 5V, with 750313769 transformer.

I use the converter with load current in 5 to 10 mA range.

If I compare my measurement results with the efficiency specification in the datasheet (Figure 20), my efficiency is much lower. The datasheet specifies an efficiency between 70 and 80%, but I measure an efficiency between 55 and 70% (i.e. more than 10% lower).

See attached document for more details.

Does someone know where this big difference comes from?

SN6501_analysis.pdf

  • 0
    TI__Genius 17100 points

    Hi Eelco,

    Thank you for posting to E2E and for sharing this detailed document of your system's schematic and measurements.

    Please add a 10uF capacitor to the center tap (pin 2) of 750313769's primary side. This will help further compensate for losses from switching, and C18 can be increased to 4.7uF.

    To maximize efficiency, ensure that routing is completed with short traces and minimal vias between components. There is also a manufacturing tolerance range of expected efficiency from one transformer part to another of the same part number; please allow me to follow up with you regarding this.


    Respectfully,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 125 points

    Hi Manuel,

    Thank your for your quick response and suggestions.

    I just tested the changes proposed by you (adding two capacitors), but this only gives an efficiency increase of 0.2% to 0.3% over the whole 0 to 10 mA load range.

    Do you have any other suggestions?

    Do you know whether an evaluation board of this converter is available, using the 750313769 transformer?

    Kind regards,
    Eelco Simonse

  • 0 in reply to Eelco Simonse
    TI__Genius 17100 points

    Hi Eelco,

    I understand. Thank you for implementing this suggestion and testing.

    Although we do not have a test PCB with this transformer populated, an SN6505B evaluation module can be modified with the SN6501 and 750313769 transformer to capture these measurements. May I contact you via PM or at the email address associated with your myTI account to follow up on this?

    Transformer tolerances in efficiency are not expected to vary by as much as 10%, so it's possible this is layout-dependent. If you can, please share photos of the PCB top and bottom layers for further analysis.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    Prodigy 125 points

    Hi Manel,

    Thank you for your response and offer to follow up.

    Yes, please send me an email at the email address associated with my account, so I can send you more information about my layout.

    Kind regards,

    Eelco Simonse

  • 0 in reply to Eelco Simonse
    TI__Genius 17100 points

    Hi Eelco,

    I have sent you an email and am looking forward to your response.

    At low loads, parasitics in cables, PCB traces, and transformer layout can make a difference in measured efficiency.

    Is it possible for you to re-capture these measurements using 4-wire power supply and meter connections to compensate for losses due to external cables? Please let me know if this is already the case.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Genius 17100 points

    Hi all,

    This conversation has been moved to email. Upon completion of this debug, I will follow up and post a summary.


    Thank you,
    Manuel Chavez

  • 0 in reply to Manuel Chavez
    TI__Genius 17100 points

    Hi Eelco, all,

    This debug activity is ongoing. We are evaluating data using 4-wire measurements and layout differences between this PCB and TI's evaluation modules.

    I am closing this thread before it is automatically locked, but please feel free to use the red and yellow buttons in the top right corner of this window to ask a new or related question.


    Respectfully,
    Manuel Chavez