5V Synchronous Buck Converter Review

[dindondee]

Hello,

Hope you're well! I have a PCB design assembled but there seems to be not enough current to power some devices on the board. I used a Synchronous Buck Converter and being that it is my first time using one of those devices (normally use LDO) I will like to ask for help on why I cannot seem to get enough current.

Could the inductor or other components around the 5V regulator be the problem? Here is the schematic of the power on the board I appreciate any help with this, thanks.

This is the regulator used https://www.mouser.com/ProductDetail/Diodes-Incorporated/AP63205WU-7?qs=u16ybLDytRZtkj8PzdWCOw%3D%3D
Inductor used https://www.digikey.com/en/products/detail/murata-electronics/1255AY-100M-P3/5271441

[Faranight]

Can you show the PCB layout?
What kind of current are you drawing?

[dindondee]

Can you show the PCB layout?
What kind of current are you drawing?

PSU shows I am drawing less than 0.19A @ 6V. I need to power a Compute module 4 and a bunch of LED's but the rated 5V 2A of the buck converter does not seem to power much even though I have 5V at the output... I have also attached other load to the output with some wiring, and the current draw barely goes up while they are not powered (low current perhaps?)

Here are some pictures, the top layer with and without polygon fill...

[mariush]

I think 10uF is a bit too much.
62305 is running at 1 Mhz so 10uH is probably not needed. Rather go down in inductance and pick something with lower DC resistance

Probably something like this would work : https://www.digikey.com/en/products/detail/sumida-america-inc/CDMC6D28NP-4R7MC/2620811  or https://www.digikey.com/en/products/detail/vishay-dale/IHLP2525CZER4R7M11/1220682  or maybe this 6.8uF one if you want cheaper : https://www.digikey.com/en/products/detail/tdk-corporation/VLS6045EX-6R8M/5287380

I don't like that trace going under the inductor and it's not clear to me if you have some ground fill under the chip or not - check the datasheet and recommended layout for that.
Also not a fan of all those output capacitors using vias .. i'd probably have a thick ground trace connecting those and then have a few vias at the end of the thick trace going to the bottom layer, if you don't want to keep a ground trace on top.

Make sure the ceramic capacitors are rated for the proper voltage, maybe at least 25v rated even though the output is only 5v.
Do you really need 9 capacitors on output? maybe consider  mixing the ceramics with a polymer capacitor ... ex a 0.1uF, a 10uF, a 22uF ceramic and then add a 47uF polymer ex https://www.digikey.com/en/products/detail/aishi-capacitors/SA10JM470A19R25XXX/16536382  ... maybe even just one 0.1uF and the 22uF and the polymer capacitor.

[dindondee]

I think 10uF is a bit too much.
62305 is running at 1 Mhz so 10uH is probably not needed. Rather go down in inductance and pick something with lower DC resistance

Probably something like this would work : https://www.digikey.com/en/products/detail/sumida-america-inc/CDMC6D28NP-4R7MC/2620811  or https://www.digikey.com/en/products/detail/vishay-dale/IHLP2525CZER4R7M11/1220682  or maybe this 6.8uF one if you want cheaper : https://www.digikey.com/en/products/detail/tdk-corporation/VLS6045EX-6R8M/5287380

I don't like that trace going under the inductor and it's not clear to me if you have some ground fill under the chip or not - check the datasheet and recommended layout for that.
Also not a fan of all those output capacitors using vias .. i'd probably have a thick ground trace connecting those and then have a few vias at the end of the thick trace going to the bottom layer, if you don't want to keep a ground trace on top.

Make sure the ceramic capacitors are rated for the proper voltage, maybe at least 25v rated even though the output is only 5v.
Do you really need 9 capacitors on output? maybe consider  mixing the ceramics with a polymer capacitor ... ex a 0.1uF, a 10uF, a 22uF ceramic and then add a 47uF polymer ex https://www.digikey.com/en/products/detail/aishi-capacitors/SA10JM470A19R25XXX/16536382  ... maybe even just one 0.1uF and the 22uF and the polymer capacitor.

Thank you mariush, your reply is quite insightful. Yes, there is a ground fill under the chip and those capacitors are actually connected to a ground plane as well. I just added the vias for thermal mass distribution when I was using a LDO on a previous revision. It is my understanding that the capacitors would help with filtering as seen in the schematic of the RPi CM4 I/O board. Those caps are rated 16v I believe...

In the next board revision, I will stick with your recommendations. Before then, I will place order for the inductors and provide feedback on the 5v output. Thank you again!

[Faranight]

I wonder... any chance you could test just the PSU part of the board by hooking up a DC load or at least a variable resistor on the output and see the current drain on input/output and the output voltage while you slowly lower the resistance? Don't exceed the maximum spec though.

[Ice-Tea]

PSU shows I am drawing less than 0.19A @ 6V. I need to power a Compute module 4 and a bunch of LED's but the rated 5V 2A of the buck converter does not seem to power much even though I have 5V at the output... I have also attached other load to the output with some wiring, and the current draw barely goes up while they are not powered (low current perhaps?)

Here are some pictures, the top layer with and without polygon fill...

This is a somewhat confusing statement... If you have 5V at the output, it would seem the converter is doing its job just fine? Unless the output colapses under load, it would seem your gizmo is just not drawing as much power as you thought it would?

[Siwastaja]

Remove that mess of different capacitors in parallel. Use only one value. Some prefer 1206 or 1210 package, but I usually use 0805 and just more of them in parallel to get the desired capacity.

Of course, if Vin and Vout are significantly different, then the input caps will be different part than output caps, and that's fine.

Layout: make the input and output side-by-side, not "from left to right" like it is now. You can get all the capacitors closer to each other.

[dindondee]

Remove that mess of different capacitors in parallel. Use only one value. Some prefer 1206 or 1210 package, but I usually use 0805 and just more of them in parallel to get the desired capacity.

Of course, if Vin and Vout are significantly different, then the input caps will be different part than output caps, and that's fine.

Layout: make the input and output side-by-side, not "from left to right" like it is now. You can get all the capacitors closer to each other.

I don't like that trace going under the inductor and it's not clear to me if you have some ground fill under the chip or not - check the datasheet and recommended layout for that.
Also not a fan of all those output capacitors using vias .. i'd probably have a thick ground trace connecting those and then have a few vias at the end of the thick trace going to the bottom layer, if you don't want to keep a ground trace on top.

Make sure the ceramic capacitors are rated for the proper voltage, maybe at least 25v rated even though the output is only 5v.
Do you really need 9 capacitors on output? maybe consider  mixing the ceramics with a polymer capacitor ... ex a 0.1uF, a 10uF, a 22uF ceramic and then add a 47uF polymer ex https://www.digikey.com/en/products/detail/aishi-capacitors/SA10JM470A19R25XXX/16536382  ... maybe even just one 0.1uF and the 22uF and the polymer capacitor.

Can you show the PCB layout?
What kind of current are you drawing?

Thank you all for your suggestions. I decided to start afresh. This time, I have taken all the recommendations and redesigned the layout- there are less output capacitors and more polygon pours. There will be via's for the ground pads and another ground pour over the top layer that will connect all ground pads.

I am also using a new Buck IC : https://www.digikey.com/en/products/detail/diodes-incorporated/AP62301Z6-7/12349219
and the inductor : https://www.digikey.com/en/products/detail/panasonic-electronic-components/ETQ-P3M3R3KVN/6134785

Here is the new layout. Thanks again!

[Wolfram]

Is there a way to show both the components and the planes interconnecting them? The layout images are very hard to read when one shows only pads and traces without any planes or component outlines, and the other one only shows copper planes without any indication of where the component pads are.

[dindondee]

Is there a way to show both the components and the planes interconnecting them? The layout images are very hard to read when one shows only pads and traces without any planes or component outlines, and the other one only shows copper planes without any indication of where the component pads are.

Yes, here they are..