WEBENCH® Tools/LM3488: BOOST circuit not used

Hi Jason,

Can you check your input current limit of your power supply and adjust it higher? I think you are hitting the power supply's current limit.

Thanks,

Richard

Hi, Richard

   The  input current limit is higher enough, The load is connected to a 50 ohm power resistor, and the output power is about 12W. The input is 15V/2A and the power is sufficient. But still pull down to constant current mode.

Hi Jason,

When you say the output voltage is not correct, what voltage are you seeing?

Can you take a picture of your hardware test setup? I'm thinking there may be an issue with either your power supply or the physical board because the circuit schematic seems to be ok.

I would check the board and see if there is a short anywhere. Is your power resistor rated for the appropriate power?

Then I would check the power supply. 

Is your power supply operating in constant voltage, constant current, or constant power mode?

Does this issue still occur if you turn on the power supply and then connect your circuit?

Does this issue occur if you use a different power supply?

If the issue is still repeatable, then this may be a circuit schematic issue.

Does replacing the 330uF input capacitor with a lower capacitance, maybe around 47uF, solve this issue?

When you have a big discharged capacitor, it will seem like a short at startup, which can cause your power supply to source a lot of current to charge this capacitor, which may be the source of the issue you are seeing.

Thanks,

Richard

Hi, Richard

  The DC power I used defaults to constant voltage mode, but is pulled to constant current mode when the current exceeds the maximum current. The input used in this test is set to 16.8V/3.361A. It will also be pulled down to constant current mode when no load is present. there still have the problem when i  replace the 330uf capacitor with 82uf. i check the borad and no short circuit was found.

Hi Jason,

Thanks for showing the photos and giving more information. 

"The input used in this test is set to 16.8V/3.361A. It will also be pulled down to constant current mode when no load is present."

That seems very odd behavior for a power supply. 

Can you verify this behavior with a different power supply? 

Thanks,

Richard

Hi, Richard

  I only have this DC power supply now. This DC power supply works normally. I used it to test other boost modules.and it is working normaly.

Hi Jason,

In that case, can you take a scope shot of the switch node and comp during the non-working conditions? That will help find out where the circuit is not functioning as is.

Thanks,

Richard