[Power supply column] No. 9 What is correct component placement? ~A tragedy caused by incorrect placement~

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Basic Power SupplyAnalog Devices

This is Sasaki in charge of power supply dock technology.

In this column, I would like to introduce some examples of problems related to power supplies that I encountered multiple times during various customer support sessions.

One day we received an inquiry saying, "There is no output from the small step-down DC/DC converter."

What Causes Abnormal Fever?

Click here for detailed symptoms

Output (3.3V) can be obtained normally when the load current is small
If you try to increase the load current to the IC rating of 3A, the IC will heat up at about 2A and the output will drop to 0V.
When it gets hot, it becomes so hot that you can't touch it with your hands

Since the heat is so great, could the output have stopped due to thermal shutdown?

The IC is rated at 3A, and even if you calculate it based on the data sheet specifications, it is hard to imagine that the temperature would rise this much.

I thought a small IC would be fine, so I tried using it, but it's useless.

Are there any differences between the manufacturer's evaluation board and the actual device?

The evaluation board outputs (3.3V) without any problems up to 3A.
However, in our actual machine, as explained earlier, the output becomes 0V at 2A or more.

Check with actual machine

The IC surface is certainly hot, and the output has dropped to 0V.
This board has 2 layers, right?

So that's it. I know the reason.
Could you raise the load current slowly from the no-load state again?

The customer and I watching the actual machine...

Ah! Oscillating!