LM3488: The design issue for LM3488

Hi Zhang,

Thanks for using the e2e forum.
Could you provide me the datasheet of the inductor?

Could you also fill in our quickstart calculator tool for this LM3488 design?
https://www.ti.com/tool/download/LM3478-88-BOOST-CALC

Based on this information, we can look into possible root causes for the strong temperature increase.

Thanks and best regards,
Niklas

Hi Niklas,

Plesae refer to the form and datasheet:

LM3478-88_Quickstart_Calculator_Boost_V1_0_0(1)(3).xlsx

3301.MCPG0565Z4R7M STD(1).pdf

Hi Zhang,

Thanks for providing the files.
Here are my comments:
- For a switching frequency of 200kHz, 4.7uH inductance is rather low. I would recommend to increase fsw to 400kHz to reduce inductor peak current (R78 --> 40kOhm).
- The compensation network might have low stability. I would recommend to adjust the values to increase phase margin.
Example values:
R79: 0.5 kOhm
C80: 500nF
C79: 6nF
- The duty cycle will be above 50%, so subharmonic oscillation is possible. To confirm if this is the root cause for strong heat-up, they would need to take a measurement of the switch node (or Vds of the FET) and check if the duty cycle is constant or oscillates.
To solve it, they would need to increase the slope compensation resistor (R62)

I would go through these changes one by one and check if the behavior improves.
If these changes do not fix the temperature problem, we can look into the layout as well.

Best regards,
Niklas