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PMP21274: PMP21274 reference design with no load testing

Part Number: PMP21274

Hi,

Base on TI PMP21274 reference design schematic, we build PCBA to testing thermal but find out have high Temp issue (~90 degree for Inductor).

But rework MODE pin to GND then got normal temp for inductor (~45 degree).

May I know if have any thermal testing report about no load condition when MODE is VCC?

Or have other suggestion for our check again.

Thanks.

Regards,

Eric

  • Hi Eric,

    Thanks for reaching out to us.

    When Mode pin is tied to VCC, you are running FPWM mode, which means both low side and high side FETs are on alternately for 100% in 1 switching cycle. Which also means the inductor is charging and discharging peak to peak current (a triangle wave, and amplitude is based on Fsw and inductance), in FPWM mode, in general you will see roughly 2 to 3 watts of input power based on your FET and inductor selection.

    When Mode pin is tied to GND, device is running diode emulation mode, which means when the low side FET is off, inductor starts to discharge current, when the current hits zero before the switching cycle ends, the high side FET turns off for the reminder of the switching period to not allow negative current flow, which also helps to save efficiency.

    You can read more about the different modes in the datasheet.

    Best regards,

    Max  

  • Hi Max:

    Thanks your explain about different mode.

    Yes, I can see the input power at FPWM mode then also got heating inductor with no load.

    May I know if have any risk about FPWM mode besides heating?

    If have any possible to add thermal waveform with no load FPWM Mode to datasheet?

    Thanks.

    Regards,

    Eric

  • Hi Eric,

    There is no risk associated with FPWM mode beside high no load power consumption, but it offers advantage such as fix frequency throughout the entire load range. 

    Inductor thermal has to do with inductance, Fsw, DCR of the inductor, core material of the inductor, I can run some thermal on my PMP21274 at 12Vin no load, I expect the inductor should be around 60oC.

    Best regards,

    Max

  • Hi Max,

    Thanks your help and would you also kindly to do 24Vin no load testing?

    BTW, I attach current Inductor spec(SC7236D-110MHF) for your check again.

    If you can provide some suggestion for our check again?

    Thanks.

    SC7236D Series_Rev_A_HF_ITG_160519.pdf

    Regards,

    Eric

  • Hi Eric,

    Please check your switch node using oscilloscope, make sure it is switching properly, amplitude should be Vout, duty cycle should be 1-(Vin/Vout), and the duty on for boost is when switch node is low.

    12Vin

      

    24Vin

    These two thermal plots were taken at no load after thermal equilibrium, on PMP21274 PCB.

    Max

  • Hi Max,

    Thanks your support. We will check it again.

    Thanks.

    Regards,

    Eric