Yes circuit do have those nets I just hid the labels
Useing several board is a long term solution
I just was just want it variable 
no solid reason
Will make a small revision in few days letâs see how it turns out
1 Like
Yes! In a boost converter, the input current all passes through the inductor, so there is not so much activity at the inductor input. The switching happens at the inductor output, and that is where the âhot loopâ is.
In a buck converter, the hot loop is at the input of the inductor.
Yes I have been doing this for > 40 years but I would greatly prefer to explain it adequately as opposed to asking you to take my word for it.
Solid ground plane as you show ought to be good. I was trying to say that the ground plane ought to at least cover the bottom side copper area underneath the âhot loopâ that I described.
FunnyâŚI google the topic âboost converter hot loopâ and this came up near the top. Maybe because google knew it was me and found my nameâŚ
1 Like
Is that anything like a buckboard?
Makes no sense but funny as heck! 
My âAre you sure?â was about:
In my opinion it goes back to input capacitor and not to IC gnd pin.
Ny two eurocents:
When switch closed:
input (cap) + â inductor â IC switch â IC gnd â input (cap) gnd.
On the output side the output cap. supplies the load independently.
When switch open:
input (cap) + â inductor â diode â output (cap) + â output (cap) gnd â input (cap) gnd.
While everyone is entitled to their opinion, I am giving you electronics theory that has been proven in the lab. Opinions are likely to be right or wrong in such situationsâŚ
Perhaps my use of the term âAC Currentâ is not the best, because I am discussing AC current (or at least the AC component of the current) through the diode for example. Instead of AC, think of rapid changes in current flow = high dI/dt. So really the critical concern is the path of high dI/dt. That certainly passes through the IC, its switchnode pin, and its ground pin when the FET is internal to the IC.
In a boost converter producing 5 Amps of output current, you could get a peak of 12 Amps passing through the switching FET (may be inside the IC) to its ground pin. This current can change to zero in 20 nSec so you get dI/dt = 600 mA/nSec through the FET drain and source, or IC ground pin if we are discussing an IC with internal FET. If you have 10 nH in series with either of these pins, that will produce a 6V spike which could cause a lot of noise or even exceed the FET voltage rating if you did not have much margin to begin with.
The inductor will not have high dI/dt passing through it, and it is an inductor anyway. So layout inductance there just increases the total inductance slightly.
1 Like
That definitely seems right will do some
More layout according to many advice I was given
Seems like having output cap and IC GND to via to ground plane can have consciousness
And yes datasheet do say to keep input loop close as possible
Some what difference questions
Do PCB price differ from different shape to shape? But over all same surface area
If shapes you have in mind are all rectangular with the same area but different side ratio and you think of mass production then you can assume price will be the same.
PCBs are manufactured by putting many of them together at one panel with factory default size (they can use several typical sizes). And I suppose you can assume panel price being the same and the question is how many PCBs are at one panel. Some shapes can force you to waste large areas.
If you are speaking about ordering few PCBs than each companyâs price policy may be different.
I have never ordered in China but I remember some offers that had constant price provided your PCB is under 10x10cm. So price for 3x3cm was the same as for 10x10cm so definitely not the same for area.
1 Like
Nobody is questioning it. IC gnd pin has to have low impedance connection to gnd pin of input capacitor. Diode cathode has to have good connection to output capacitor and output capacitor gnd pin has to have good connection to input capacitor gnd pin.
If both (IC gnd pin and output capacitor gnd pin) have to have good connection to input capacitor gnd pin than as the result they also have good connection between them but it is only âside effectâ.
The current pulses of switching Mosfet flows from IC gnd pin to input capacitor gnd pin. And their AC part (their dI/dt) is also connected with that circuit and not with connection between output capacitor gnd pin and IC gnd pin.
What I was asking was about what you have written:
I supposed that may be you are speaking about something I donât know and my nature is that if I find something (in electronic) I donât know I want to learn it (until it is not too complicated for me). Now I suppose it was just a slight inaccuracy in the statement.
No. The input capacitor does not see severe pulsing because its current is filtered by the inductor. It is the output capacitor that gets the current pulses.
Letâs see if I understand:
The current from the inductor goes through the diode into the output capacitor (+).
The other half of the loop is output capacitor gnd, input capacitor gnd and input capacitor (+) to inductor input side.
The highest dI/dt as well as ripple amplitude is on the mosfet and the diode, as they alternate between zero and a maximum current depending on load, input/output voltages etc. and the transition is fast.
Ripple current on the input capacitor and inductor is less, as there is always some current flowing; either the current delivered to the diode or the current drawn by the mosfet.
That is closer. The fact is that the inductor current CAN go to zero if the converter is operating in Discontinuous Conduction Mode (DCM). But the slope of the inductor current (dI/dt) should be much slower. And inductance in the inductorâŚis expected (the circuit is designed for it.)
The input current goes either into the diode or the MOSFET drain, depending on whether the FET is turned ON or OFF. The point is that those transitions are very rapid in Amperes per nanosecond. The output capacitor and the MOSFET drain and source pins all handle that high dI/dt.
And this is the key argument. You were really speaking about something I didnât took into account. It is probably so obvious for you that you had a problem to understand what I donât understand.
So if we have these 3 elements (input capacitor, output capacitor, IC gnd pin) connected to one point then current from input capacitor is relatively constant and both others switch dramatically fast. So even both these currents flow from input capacitor we really can say that high frequency switching pulses flow from output capacitor to IC gnd pin. So the impedance of connection from input capacitor to that common pint is not so important and both others are much, much more important.
Now I think of it differently than today morning 
1 Like
Ripple current (triangular current shape in inductor) is not important here - can be ignored at all. As the source of high frequency pulses is switching action you can assume input capacitor and inductor current being constant during the whole switch takes place.
Hi, Piotr
While the inductor ripple current (and input ripple current) is much less severe, I think it goes too far to say that it does not matter at all.
But I think that you are now getting my point with regards to the severe dI/dt.
This was a buck regulator, but I once had a failed design due (I think) to the lead inductance in I-pak MOSFETs. Voltage spikes causing device avalanche. The MOSFETs were overheating. I think the leads might have been 5 mm long each. Because the FETs are switching hi dI/dt, minimum inductance in series with MOSFET source and drain lead are critical in (I am thinking all switching power converter topologies.).
https://www.digikey.com/en/products/detail/stmicroelectronics/STU6N90K5/6616053
