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I designed the circuit as follows. I used a 2.2uH inductor with a 19mohm DCR and a 4.9A Isat, and added a 220pF capacitor to the feed forward path for stability. However, it cannot provide a 5V, 1A output at a 2.7V input; the output drops to zero. It can only output a maximum of 800mA, which is significantly lower than the efficiency shown in the datasheet. The output capacitor is 100uF, and it's all integrated into the IC, making it difficult to debug. Please help me figure out what the problem might be.
Furthermore, when I gradually increase the load at a 2V input (around 400mA), it switches at 1MHz initially but then drops to 700kHz, and again the output falls to zero. Please help me.
We use 100uF ceramic cap and have changed it to 20uF but the problem was not resolved.
I include the layout.
Hi Junghyun,
It seems like to due to the poor layout. As I said, please place the output cap as close as VOUT pin, so the area of SW-COUT-VOUT-GND loop (so called critical, red one below) is as much as small.
You can take this layout as reference.
You can also take this app note for more detailed info about layout.
Regards,
Nathan
Thanks for your reply
I think the output cap is not too far from VOUT pin in my layout.
Is this small difference such a critical?
Hi Junghyun,
Yes the loop is the most important loop for our IC, you can refer to the app notes I mentioned above.
And the loop in your board is double the size of the recommend one, and more I suggest that you can use a small cap, like 10uF or 22uF paralleled with the big 100 cap, and place the small cap as close as VOUT pin.
Regards,
Nathan
