Author Topic: AP63203WU-7 layout review  (Read 1777 times)

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Online k0ckaTopic starter

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AP63203WU-7 layout review
« on: April 21, 2024, 12:24:30 pm »
Hello everyone!

I just finished my first buck converter layout and I would really appreciate some feedback. I wasn't sure if I should post this in the beginners category or here, so I hope I chose the right place.
I decided to use the AP63203WU-7 because it seemed like the best and easiest option for me. My input voltage will be 12V or 24V, output voltage 3.3V and the maximum output current 1A. I'm not sure about the GND vias below the inductor, I added them for heat dissipation but I don't know if they are necessary or if I should remove them.

Components I used in the layout:

Thermal fuse - https://www.lcsc.com/product-detail/Resettable-Fuses_BHFUSE-BSMD1206-100-30V_C5358568.html (U1)

Protection diode - https://www.lcsc.com/product-detail/Diodes-General-Purpose_TWGMC-1N4001_C727079.html (D2)

Input capacitors - https://www.lcsc.com/product-detail/Aluminum-Electrolytic-Capacitors-SMD_ROQANG-CK1A470M-CRC54_C3001223.html (C5),
                        - https://www.lcsc.com/product-detail/Multilayer-Ceramic-Capacitors-MLCC-SMD-SMT_Samsung-Electro-Mechanics-CL31A106KBHNNNE_C13585.html (C1)

Buck IC - https://www.lcsc.com/product-detail/DC-DC-Converters_Diodes-Incorporated-AP63203WU-7_C780769.html (U3)

BST capacitor - https://www.lcsc.com/product-detail/Multilayer-Ceramic-Capacitors-MLCC-SMD-SMT_Samsung-Electro-Mechanics-CL10B104KB8NNNC_C1591.html (C3)

Inductor - https://www.lcsc.com/product-detail/Power-Inductors_cjiang-Changjiang-Microelectronics-Tech-FXL0530-4R7-M_C177246.html (L2)

Output capacitors - https://www.lcsc.com/product-detail/Multilayer-Ceramic-Capacitors-MLCC-SMD-SMT_Samsung-Electro-Mechanics-CL31A226KOHNNNE_C90146.html (C2,C4)

2132894-0
 

Offline mariush

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Re: AP63203WU-7 layout review
« Reply #1 on: April 21, 2024, 12:45:08 pm »
Negative  on C5 ...  47uF 10v rated from a noname chinese brand ... first of all it's lower voltage rating than 12v or 24v, so your be damaged right away.. second its specs are crap

Try something like https://www.lcsc.com/product-detail/Solid-Capacitors_AISHI-Aihua-Group-SPZ1VM101E08O00RAXXX_C122240.html  or https://www.lcsc.com/product-detail/Solid-Capacitors_AISHI-Aihua-Group-SPZ1HM101F09O00RAXXX_C171434.html  or if you insist on surface mount, this apaq 47uF 35v rated one that's slightly bigger at D6.3xL5.8mm  : https://www.lcsc.com/product-detail/Solid-Capacitors_APAQ-Tech-350AVCA470M0606E38_C494513.html

The fuse is kinda high current... I mean .. 3.3v at 1A is 3.3w ... 3.3v/12v = 0.275a ... so probably even a 0.5A fuse would do, but if you want to support wider input voltage range I guess it's fine.

The rest ... some people say it's best to not have ground copper pour under the inductor (on the other side of the pcb is fine) ... I don't think it matters that much but I wouldn't put vias right under the inductor.

The output capacitors are good enough.  Consider adding a through hole footprint just in case you'd want to add a small through hole polymer cap there... it's free, you have space, and you can just leave it unpopulated if you don't feel it's needed.
 
 
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Online k0ckaTopic starter

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Re: AP63203WU-7 layout review
« Reply #2 on: April 21, 2024, 01:41:30 pm »
Quote
Negative  on C5 ...  47uF 10v rated from a noname chinese brand ... first of all it's lower voltage rating than 12v or 24v, so your be damaged right away.. second its specs are crap
I must have overseen it, I thought it's 100V. Thank you for pointing it out! I will go with the third option. Can I ask, how do you select components like capacitors? (except from voltage rating and capacitance)

Quote
The fuse is kinda high current... I mean .. 3.3v at 1A is 3.3w ... 3.3v/12v = 0.275a ... so probably even a 0.5A fuse would do, but if you want to support wider input voltage range I guess it's fine.
Oh of course, I didn't consider the voltage drop, so the 1A fuse would be more suitable for the output side right? But I think I will just replace the one on the input for 0.5A as you mentioned.

Quote
The rest ... some people say it's best to not have ground copper pour under the inductor (on the other side of the pcb is fine) ... I don't think it matters that much but I wouldn't put vias right under the inductor.
Ok I will remove the vias, thank you for clarifying.

Quote
Consider adding a through hole footprint just in case you'd want to add a small through hole polymer cap there...
Yeah I can add the footprint for sure -  could you explain why is it needed though?
 

Offline mariush

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Re: AP63203WU-7 layout review
« Reply #3 on: April 21, 2024, 03:00:47 pm »

I must have overseen it, I thought it's 100V. Thank you for pointing it out! I will go with the third option. Can I ask, how do you select components like capacitors? (except from voltage rating and capacitance)

I'm not an expert on capacitor selection. Basically what I do is carefully read datasheets and try to understand what they're saying, and by what I learned from repairing electronics, seeing other designers do pcb layouts for switching regulators etc etc 

Your 10uF ceramic capacitors satisfy the minimum input capacitance requirement of the regulator, but they're all very low ESR and when you power such circuits through long leads the inductance of such leads can cause issues, so it's a good practice to add a capacitor with higher ESR.  The polymer capacitors I recommended are not ideal, because it's still quite low ESR at 40-50 mOhm (but still 25-50x higher than ceramic capacitors), I think around 100-200 mOhm would be better ... but to get that with electrolytic capacitors you'd need to go up to around 100-270uF 35v and those get kinda big... I feel what I suggested is fine. 

See also the notes in the datasheet at page 13: https://www.diodes.com/assets/Datasheets/AP63200-AP63201-AP63203-AP63205.pdf

Quote
"The input capacitor reduces the surge current drawn from the input supply as well as the switching noise from the device. The input capacitor has
to sustain the ripple current produced during the on time of Q1. It must have a low ESR to minimize the losses.
The RMS current rating of the input capacitor is a critical parameter and must be higher than the RMS input current. As a rule of thumb, select an
input capacitor which has an RMS rating greater than half of the maximum load current.

The ceramic capacitor has the low esr to minimize losses and is adequate. The electrolytic or polymer is in parallel, and can have higher ESR to absorb what the ceramics can't handle, but they must also have that RMS current rating high enough .. as the comment says should be greater than half the load current - yours would be 1A, so the RMS current should be at least 500mA or better ... so your capacitor, even if it was rated for 50v or 100v, is really lousy at RMS current. Polymers are much better in that department , the apaq is good for up to 2.1A ripple current, that's quite a lot.


Quote
The fuse is kinda high current... I mean .. 3.3v at 1A is 3.3w ... 3.3v/12v = 0.275a ... so probably even a 0.5A fuse would do, but if you want to support wider input voltage range I guess it's fine.
Oh of course, I didn't consider the voltage drop, so the 1A fuse would be more suitable for the output side right? But I think I will just replace the one on the input for 0.5A as you mentioned.

Your switching regulator is not 100% efficient and may consume current in bursts, so the way I calculated is overly simplified... I was going by your comment that will be powered by 12v or 24v but 1A setting at the input is reasonable ... you may want to use a 7.5v or 9v adapter and then you'd have higher input currents. 

I'd say leave it at 1A, it's a good choice.


Quote
Consider adding a through hole footprint just in case you'd want to add a small through hole polymer cap there...
Yeah I can add the footprint for sure -  could you explain why is it needed though?

Well if you look at the datasheet again at page 14, it says
Quote
The output capacitor keeps the output voltage ripple small, ensures feedback loop stability, and reduces the overshoot/undershoot of the output
voltage during load transients. During the first few milliseconds of a load transient, the output capacitor supplies the current to the load. The
converter recognizes the load transient and sets the duty cycle to maximum but the current slope is limited by the inductor value.
..
An output capacitor with large capacitance and low ESR is the best option. For most applications, a 22μF to 68μF ceramic capacitor is sufficient.

So 22-68uF is SUFFICIENT,  as in you'll satisfy the minimum recommended of 22uF with 2 ceramic capacitors in parallel (because the actual capacitance varies with voltage and temperature in ceramic capacitors) and the voltage fluctuations on output will be minimal, good enough, but there's no rule against adding a bit of capacitance to get extra smooth output voltage, less overshoot/undershoot if whatever you have connected to the regulator pulls sudden bursts of power from the regulator. IF you find you don't need it, you can simply leave the footprint unpopulated.


 
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Online k0ckaTopic starter

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Re: AP63203WU-7 layout review
« Reply #4 on: April 21, 2024, 07:18:12 pm »
Thank you for your detailed reply, I appreciate it!

Based on your suggestions, I replaced the C5 with 350AVCA470M0606E38, added footprint for C6 polymer capacitor and removed the vias below the inductor as shown in the attachment.

One more thing I wanted to ask about is the reverse polarity protection in my circuit - on another forum I was told that the diode I used is not the right fit for my purpose and that I should use P-channel mosfet in combination with zener diode. I went for the solution with the 1N4001 diode because I tried to keep it as small as possible and I found it mentioned on another forum. Do you think I should go for the mosfet or can I stick with the diode?

« Last Edit: April 21, 2024, 07:21:14 pm by k0cka »
 

Offline HwAoRrDk

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Re: AP63203WU-7 layout review
« Reply #5 on: April 21, 2024, 10:48:50 pm »
One more thing I wanted to ask about is the reverse polarity protection in my circuit - on another forum I was told that the diode I used is not the right fit for my purpose and that I should use P-channel mosfet in combination with zener diode. I went for the solution with the 1N4001 diode because I tried to keep it as small as possible and I found it mentioned on another forum. Do you think I should go for the mosfet or can I stick with the diode?

Your polarity protection is fine, but with the caveat that the fuse will be blown when a reverse polarity event occurs. That's how it works: the diode essentially forms a short circuit between ground and power (but not in normal polarity), and relies on enough current to flow to blow the fuse and break the circuit. The other thing is to ensure the diode can withstand the current necessary to blow the fuse - otherwise your diode becomes the fuse. :)

Maybe you could consider using a PTC resettable fuse instead, so your board isn't dead after someone accidentally reverses polarity.

A 1N4001 should be fine if you have a 0.5A fuse, because most 1N400x are 1A continuous rated, and higher for surge current.

A P-ch MOSFET is a different kind of polarity protection. It non-destructively prevents current flow in the reverse direction in the first place. The FET is placed in series with the positive, drain on the supply side, source on the load side. Gate is connected to negative via a resistor. Zener diode is placed between source and gate to protect from overvoltage damaging the FET.

In normal polarity the FET effectively turns itself on through current flowing via the parasitic body diode, forming a low-resistance path with minimal voltage drop. In reverse, the FET is held off, never completing the circuit.

https://hackaday.com/2011/12/06/reverse-voltage-protection-with-a-p-fet/
« Last Edit: April 21, 2024, 10:59:57 pm by HwAoRrDk »
 
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Online k0ckaTopic starter

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Re: AP63203WU-7 layout review
« Reply #6 on: April 21, 2024, 11:19:00 pm »
I would like to keep the 1A fuse, so I think I will replace the diode. What about this one for example - https://www.lcsc.com/mobile/product-detail/Diodes-General-Purpose_MSKSEMI-SK34_C5140034.html

And isn’t the fuse I have chosen also resettable?
 

Offline HwAoRrDk

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Re: AP63203WU-7 layout review
« Reply #7 on: April 22, 2024, 03:33:46 am »
I would like to keep the 1A fuse, so I think I will replace the diode. What about this one for example - https://www.lcsc.com/mobile/product-detail/Diodes-General-Purpose_MSKSEMI-SK34_C5140034.html

Sure, that would be good. Although it does have 20x the leakage current, but it's still only 100 uA, which isn't anything significant for this application. If you have room, a physically larger diode with higher surge rating, something like an SMB or even SMC package, would be belt-n-braces.

And isn’t the fuse I have chosen also resettable?

Oh, so it is. I didn't see the link, sorry.

That fuse datasheet is weird. In the table, the BSMD1206-100-30V is specified to take 300 ms to trip at 8A, but following the time-current graph curve 'J' (for BSMD1206-100) shows around 60 ms @ 8A. Which is correct? Who knows? :-// But either way, contrast to the 80A surge current rating of the diode being for only 8.3 ms.
« Last Edit: April 22, 2024, 03:46:01 am by HwAoRrDk »
 
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Online k0ckaTopic starter

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Re: AP63203WU-7 layout review
« Reply #8 on: April 22, 2024, 01:13:14 pm »
Ok, I have set the filter attributes to SMB package, reverse voltage to 24 or more and rectified current to 3A.(I also selected general purpose diode, or should I go for the schottky?) Which one would you pick from these two?

https://www.lcsc.com/product-detail/Diodes-General-Purpose_BORN-S3A_C19078059.html
https://www.lcsc.com/product-detail/Diodes-General-Purpose_Diodes-Incorporated-S3AB-13-F_C460939.html

I'm not really familiar with which brands are "good quality" in this electronic components field. I've run into Diodes Incorporated several times when I was looking for some component so I believe they're more widespread, but the price in this specific case is noticeably higher then the product from the other manufacturer. Or am I overthinking this? :D

Hmm, I checked other fuses datasheet's and the graph doesnt match the data from table. For example another one which is listed as 300ms, but in the datasheet's graph is 60ms value. - https://www.lcsc.com/product-detail/Resettable-Fuses_LUTE-1206L100-30NR_C7542958.html

And even if so, is 300ms too much?


« Last Edit: April 22, 2024, 02:57:51 pm by k0cka »
 

Offline eugene

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Re: AP63203WU-7 layout review
« Reply #9 on: April 22, 2024, 04:00:41 pm »
The rest ... some people say it's best to not have ground copper pour under the inductor (on the other side of the pcb is fine) ... I don't think it matters that much but I wouldn't put vias right under the inductor.

I'm one of those people. I found through testing with an Agilent LCR meter that a copper plane/pour below the inductor both lowers the inductance and reduces the Q. Just don't do it.
90% of quoted statistics are fictional
 


Offline AnshumanFauzdar

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Re: AP63203WU-7 layout review
« Reply #11 on: June 20, 2024, 07:48:09 am »
I am trying a similar circuit with AP63205WU-7 for 5v output, did you get your PCB fabricated and tested out?
I made mistakes in layout of the PCB and now the AP63205 is emitting smoke due to overheating!
 

Offline T3sl4co1l

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Re: AP63203WU-7 layout review
« Reply #12 on: June 20, 2024, 06:49:37 pm »
The rest ... some people say it's best to not have ground copper pour under the inductor (on the other side of the pcb is fine) ... I don't think it matters that much but I wouldn't put vias right under the inductor.

I'm one of those people. I found through testing with an Agilent LCR meter that a copper plane/pour below the inductor both lowers the inductance and reduces the Q. Just don't do it.

Of which types? How many styles have you tested?

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Bringing a project to life?  Send me a message!
 

Online k0ckaTopic starter

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Re: AP63203WU-7 layout review
« Reply #13 on: June 20, 2024, 08:44:30 pm »
Yes I did and it's working fine so far, I hope it helps you.
Can you share your layout by a chance?
 

Offline AnshumanFauzdar

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Re: AP63203WU-7 layout review
« Reply #14 on: June 21, 2024, 09:49:20 am »
Yes I did and it's working fine so far, I hope it helps you.
Can you share your layout by a chance?

Its a total disaster but I will follow your layout design and order new PCBs to test out the new design and hopefully not fry the AP62305s ;D
 


Offline ArdWar

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Re: AP63203WU-7 layout review
« Reply #16 on: June 25, 2024, 06:19:40 am »
I'd like to hear what the verdict is with copper pour below inductors.

My thought was that decent molded inductors usually have very low flux leakage that it should not matter that much. Otherwise it should wreak havoc with those dense multiphase designs.
 

Offline T3sl4co1l

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Re: AP63203WU-7 layout review
« Reply #17 on: June 25, 2024, 07:29:41 am »
Well, put it this way. Power supplies have been made with low-Q inductors for ages. Yellow powdered iron cores for example. Laminated iron going back even further (a number of PDP-11s, etc. were made with somewhat rudimentary SMPS, bipolar switch and laminated choke, low 10s kHz).  Low Q is not strictly a barrier to high efficiency.  The tradeoff is, you need to make reactive power small in relation to DC power, i.e. large inductance / low current ripple fraction.

There are only two effects to nearby copper:
1. Reduced Q of the inductor itself
2. Induced voltage in said copper

#2 we can discard easily by designing it with solid ground plane, so that the induced voltage is mostly shorted out and doesn't wind its way into signals, or common mode in nearby connectors, etc.

That leaves #1, and for typical leakage, like say, well heck let's even go worst-case and say it's an air-core inductor of modest aspect ratio (say 1:2 to 2:1), solenoidal design, and resting flush on the board.  The coupling factor (which because of the shorting plane, is also basically the inductance reduction factor) will be in the 0.2, 0.3 range for such an arrangement, maybe up to 0.5 for a squat inductor with axis normal to the plane.  Easily under 0.1 for some height above the board, and easily under 0.05 for anything with a core (even if the air gap is placed directly against the plane, cooking it by fringing field).  "Shielded" types may be in the 1% range; I think I would be surprised if anything off-the-shelf and not specifically contained (like with a flux (shorting) band around the core) would do much better than 1%; this is because k ~ k_aircore / mu_eff, and mu_eff ~ 50 for typical inductors.

Even if the plane were a perfectly matched resistor, exactly absorbing the incident field and neither reflecting nor passing it, the coil's Q due to plane effect won't be less than 1/k.  And for the real case, where copper is a pretty good reflector of field (even such low impedances as in SMPS coils, fringing field, etc.), the Q will be higher while L_loaded sees a stronger reduction instead.  (That is, as you vary R_load of a nonideal transformer, for R --> infty, you get L = Lm; for R --> 0, you get L = LL; for inbetween values, you get some mix of L (intermediate between these extremes) and reflected R, as the total impedance traces an arc on the Smith chart.)

So the verdict is:

It depends. :P

Namely, it's far more important in high-ripple, high-efficiency designs; peak current mode control, DCM, BCM, or quasi- or fully resonant types, are typical examples.  These will also be applications where litz wire on gapped ferrite are preferable over solid or edgewound wire on powder or composite cores.  Q of hundreds (thousands, even?) might be demanded.  Trying to use an unshielded inductor over solid plane, may unduly affect the Q, and efficiency is lost, operating temp rises, etc.

Low-ripple, high-inductance, average current mode, COT, etc. types can deal with lower Q, and hence the lossier materials and constructions are acceptable, and plane induction is less important.

Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
Bringing a project to life?  Send me a message!
 

Offline AnshumanFauzdar

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Re: AP63203WU-7 layout review
« Reply #18 on: July 02, 2024, 07:06:40 am »
 


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