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LM5022: Vout drop when increasing the load

Tess Chen
Intellectual 2675 points
Part Number: LM5022
Other Parts Discussed in Thread: TPS23861,

Hi, 

Power rail: 12V->LM5022->54V -> TPS23861(PSE)->PD (54V max 0.5A load) 

Please find the boost schematic in the below,  parameters are referring  to LM5022 12V input, 54V 0.5A output design from WEBENCH.

Issue: The output voltage can be stable 54V when having 1W PD device,  and  Vout has periodical drop when having more than 2W PD load.  With higher load the frequency of drop cycle become higher. The output voltage,  PIn 5 (Out) voltage, U74(Mos) output voltage and COM pin voltage are measured and shown in the following. 

Vout 


OUT PIN 5 VOLTAGE


U72 MOS OUTPUT VOLTAGE


COM PIN VOLTAGE


Could you please  give some suggestion to solve this issue? Thanks a lot.

Best Regards,

Tess Chen

 

  • 0
    TI__Mastermind 25520 points

    Hi Tess,

    Thank you for sharing the images. It looks like your COMP pin is hitting the open circuit voltage, which can happen if FB is low. Can you increase your output capacitance and see if fixes the issue? It is possible that at higher loads, your output capacitance cannot supply the needed current which will pull the output voltage down.

    Thanks,

    Richard