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LMR14203: about flywheel diode

Guru 11150 points
Part Number: LMR14203

Hello E2E,

When it used the FRD for flywheel, the power supply circuit output voltage has unstable at low temperature (Ta=-20 deg-C).
When it used the SBD, the output voltage has stable at low temp too.
I know the FRD has drift -2mV/deg-c for Vf.

Question;
We believe that fluctuations in Vf affect stability.
Can TI explain this reason?

Regards,
ACGUY

  • Hi ACGUY,

    Do you check the reverse recovery time of FRD you used?  

    Normally FRD is not suggested to use with converters whose working freq over MHz.

    Vf should not impact loop stability over temperature.

    B R

    Andy 

  • Hello Andy,

    The question is not whether the use of FRD is appropriate, but whether the characteristics of FRD at low temperatures can affect the stability of the power supply.

    Can you tell us which FRD parameters affect the stability of the power circuit at low temperatures?

    Regards,
    ACGUY

  • Hi ACGUY,

    the Vf increase only 90mV from Ta=25C to -20C as FRD has drift -2mV/deg-c for Vf,  I don't think this will impact loop stability.

    Suppose this maybe caused by the recovery time changed at low temp, smaller recovery time and higher recovery peak current at low temp will generate big ringing on SW node and noise on VIN pin, and then cause the unstable switching and output

    You may try to place 0.1uF 100V X7R cap very close to VIN pin and FRD ground, also measure SW waveform at low temp.

    B R

    Andy