This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

LM3478: The circuit gives me unstable output

Part Number: LM3478

Hi Ti community,

I posted my circuit previously and I solved the problem(Layout problem on FET) because of you guys.

I am thankful for that.

However, I came across with different issue. The circuit below provides me stable 10V output with no load. 

With 400mA load, the circuit gives me output below(The circuit draws 30mA with no load on LM3478). The output voltage measured on oscilloscope is not stable. 

The problem I am facing now is that

- The output voltage is unstable when load is applied.

- What I expected from the circuit is to draw about 1A because the power drawn by LM3478 draws 400mA with 10V.

Any feedback will be welcomed and will help me a lot!

Thank you for your help in adavance!!

  • Hi BonJae Koo,

    Thank you for posting.  It seems the circuit may high cycle by cycle peak current limit.  Can you increase C23 from 10pF to 1nF? which can filter out the leading edge current spike and avoid trigger cycle by cycle current limit.

    Thanks,

    Youhao Xi, Applications Engineering

  • Thank you Youhao.

    I changed C23 to 1nF and changed output capacitor to 220uF and it became stable.

    Now I face another problem. It turns on the LED load fine with 4V or higher input voltage. However, LEDs(which are C.C controlled) are dim and turned off  with 3.5V to 3.9V. The circuit is originally designed to have 3.5~4.2V input and 10V/1A output.

    Do you have any suggestion can solve this problem?

  • Hi,

    It still look like hitting the cycle by cycle peak limit.  Can you reduce R9 by 50% and see if you can extend the operation to a lower input voltage (3.5V?)

    Thanks,

    Youhao

  • May I assume the issue is resolved and I can close this thread?  You are welcome to re-open this thread by adding a new post or creating a new thread.

    Thanks,

    Youhao