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TPS55010 efficiency suggestions

Ed Walker
Prodigy 5 points
Other Parts Discussed in Thread: TPS55010

I have a design using the TPS55010, running at 107KHz, about 42% duty cycle, using transformer Coilcraft p/n JA4650-BL (primaries in series, secondaries in series).

Load current is 8.5mA max nominal, output 6V, input 5V.

All parts selected using TI's single output spreadsheet. I've also tried running up to 350KHz (various component values adjusted, of course).

Load current is 8.5mA max nominal.

I am getting about 76% efficiency, tops (input current ~14mA). I need to squeeze out 90-91% if I can (input current of 11.25mA max). What should I vary to get this? Reduce duty cycle (increase turns ratio)? Or reduce/increase transformer primary inductance? Some other?

Thanks,

  • 0
    TI__Mastermind 35165 points

    Hi Ed,

    You've tried most of the important things to improve the light load efficiency. To reach 90% efficiency the power loss would need to be reduced to 5 mW. At these low currents, most of the power is lost due to the operating current and the gate drive of the FETs. Which contributes to approximately 3mW with 107kHz switching frequency and 5V input. The lowest switching frequency will give the highest efficiency.

    The other big power loss contributor is the rectifying diode. Assuming 0.35V forward voltage with 8.5mA load the power loss is another 3mW. What is the diode you are using?

    A few other things you can do is to float the EN pin if it is not already or increase the resistance in the FB divider.

    Best Regards,
    Anthony

  • 0 in reply to Anthony F
    Prodigy 10 points

    Anthony,

    My name is William Pinson, an EE at NOV.  Ed submitted this question on my behalf.  The diode I am using is the MBR0530 (Fairchild & On Semi.).  I tried a couple of others to try to get the forward voltage drop down (Rohm RB161M-20 and NXP PMEG3010ER), but at switching frequency, the forward voltage of the each of these was worse than the MBR0530.  Apparenly the switching speed of these is such that they never get to their lower forward voltage before the next switching transition.

    Any suggestions on a very fast Schottky with a super-low forward voltage?  (very fast meaning that it will reach its low forward voltage in nanoseconds rather than microseconds)

    Thanks,

    William Pinson

  • 0 in reply to William Pinson
    TI__Mastermind 35165 points

    Hi William,

    Sorry I do not have any suggestions for a better diode at the moment. For this application there's not much more you can do improve the efficiency with the TPS55010 because of the low power. It was targeted more for about a 1W application and as such, the FETs are relatively low Rdson. This is much lower than is needed for low conduction losses in a low power application. This has the effect of increasing the gate charge which limits the maximum efficiency at light loads.

    Let me know if there is anything else we can do to help.

    Best Regards,
    Anthony