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LM25180: power supply unstable issue when 12v input

jasonse jia
Prodigy 10 points
Part Number: LM25180

greetings, When the LM25180 chip is used, the output is unstable at 12v input, and the target output voltage (5v) cannot be reached when the load is more than 100mA. The output is basically stable when the input voltage is increased to 24v. The sw pin waveform is first output in bcm mode for about 2 ms, and does not output after the voltage reaches about twice vin, and then cycles in a cycle of about 5 ms. Schematics are shown below.

  • 0
    TI__Mastermind 22280 points

    Hello,

    Your output capacitance looks low when compared to the similar design shown in Section 9.2.1 in the device datasheet. For a 5V, 1A converter, it is recommended to have 100uF. The transformer selection is also far off from what we recommend in the datasheet. In addition to that, the potentially large leakage inductance can negatively impact the performance of a PSR flyback converter. I would verify this by evaluating the device on the 5Vout EVM: https://www.ti.com/tool/LM5180EVM-S05

    The EVM is identical to your design, except for the output capacitance and transformer selection. 

    Best regards,

    Ridge