Too much current from a Buck Converter

[caspian]

Dear members,

Let us consider the buck-converter circuit of +1.05VS_VCCPP in the PDF. +1.05VS_VCCPP is a 1.05v voltage rail. The schematic says the circuit can provide up to 20A of current. It belongs to a laptop: Lenovo G470. B+ is 19v.
Now assume we connect +1.05VS_VCCPP to many ICs to provide power for them. The laptop works in a way that mostly less than 20A are drawn from +1.05VS_VCCPP but sometimes the required current exceeds 20A. For example, 25A or 30A.
PU702 is the controller IC in the buck-converter circuit. It controls the output voltage according to the feedback in Pin 5.

Please explain what will happen when the connected ICs try to draw more than 20A from this buck-converter circuit?
Does the buck-converter circuit provide the extra current or it just provides 20A?
Does the voltage drops at those times?
Do the Mosfets get hot?
Does any IC get damaged at those times?

Thanks

[eccerr0r]

Re: Too much current from a Buck Converter

inductor gets hot
mosfet gets hot
regulation/ripple/voltage no longer in spec, ICs no longer work properly.

Ideally it was designed with some buffer space past 20A but no guarantees.

I'm surprised that it's bucking 19V to 1.05V, that's a fairly large jump though not out of the world of impossible. 19V seems kind of a waste, lithium ion battery packs usually not 19V, so a boost converter would be necessary...

[caspian]

Re: Too much current from a Buck Converter

The 19v DC voltage is provided by the AC adapter of the laptop.
Here is the datasheet of the controller in the buck-converter circuit. In Page 12, it says RT8209 has cycle-by-cycle current limiting control. then, it explains more.
It is really important to me to know whether the extra required current leads to some damage/degradation to the buck-converter circuit and the connected ICs, or it leads to just a shutdown of the laptop?

[caspian]

Re: Too much current from a Buck Converter

In addition, I have got the following question:
The AC adapter provides 19v 4.5A as the DC power source (B+) for this buck-converter circuit. How come this buck-converter circuit is able to generate 20A? how can the buck-converter circuit generate 15.5A more current compared to its power source?