Buck Converter PCB Layout - Page 1
Forum section: electronics / projects

author: jtexbox
author_rank: Newbie
timestamp: June 20, 2025, 07:35:16 pm
content: Hello, EEVBlog.First post. I am delving into the world of DC/DC converters. Here is an initial stab at a PCB that powers a servo motor at 5.5V down from 24V via TPS54202. I am machining this PCB and hand soldering, which is why you may see a striking lack of vias and other normally included specifics. I am seeking feedback on layout and routing as it relates to having a stable buck converter. I did a lot of study of the datasheet and WEBENCH suggested layout, and I am hoping i am at least in the ballpark, considering my constraints of machining the PCB and hand soldering.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 21, 2025, 01:31:37 pm
content: With limited space/width capabilities, there's not a ton more you can do to improve it.1. Move C1 and the switching node via as close to U1 as possible.2. Put C2 on the bottom side, and move it west. This will allow that path to shrink quite a bit.3. I'd also add more input capacitance as through-hole parts straddling above the other components.

author: mariush
author_rank: Super Contributor
timestamp: June 21, 2025, 03:22:34 pm
content: Not much improvements you could do. Maybe shifting the 100nF ceramic a bit to the left and not have that tiny sliver of ground copper fill through the ceramic capacitor footprint.I wouldn't use this IC, because of the less than optimal pinout that puts the inductor further away from the chip and because of its maximum 28v input voltage - you plan to power it with 24v which is quite close to its maximum voltage. If you happen to have some voltage spikes from a long power cable for example or due to some other reasons, the IC could be damaged. The SOT-23-6 footprint also has a high-ish 90c/w thermal resistance.I'd suggest looking for example at AP63300 / AP63301 (max 3A) :https://www.digikey.com/en/products/detail/diodes-incorporated/AP63301WU-7/10491607There's also AP63200/AP63201 (max 2A) with same pinout, but it has higher Rds(on) mosfets and the 3A version is not that much more expensive.The chips are also available at LCSC for very cheap, here's AP63xxx :https://lcsc.com/products/DC-DC-Converters_484.html?globalKeyword=ap63&s_z=n_ap63Datasheet:https://www.diodes.com/assets/Datasheets/AP63300-AP63301.pdfIt has a bit better pinout by having the BST and SW pin on the same side, you can see a suggested layout on page 19There's also a fixed 5v 2A output version AP63205, but this one and the 3.3v fixed output equivalent AP63203 run at 1.1 Mhz switching frequency, so you'd use smaller inductors with those (if you want) but still need a trace from output to feedback so you're better off just having the circuit board designed for adjustable version (and if you put the fixed version on the board, you can just put a 0 ohm resistor on the feedback path instead of resistor to set the voltage.Richtek RT6283B is another OK option, in SOP-8 package with better 50c/w thermal resistance :https://www.digikey.com/en/products/detail/richtek-usa-inc/RT6283BGSP/16376737or a third of the price at lcsc :https://www.lcsc.com/product-detail/DC-DC-Converters_Richtek-Tech-RT6283BGSP_C3001126.html?s_z=n_ap63Datasheet:https://lcsc.com/datasheet/lcsc_datasheet_2410121914_Richtek-Tech-RT6283BGSP_C3001126.pdfUp to 30v input voltage.... you'd have to add a ceramic capacitor and a resistor for compensation and a resistor to set the current limit, but passives are cheap. BST and SW pins are also close together, for simpler layout, the SW pin is on the corner, making it possible to put the inductor very close to the pin.

author: jtexbox
author_rank: Newbie
timestamp: June 21, 2025, 04:08:28 pm
content: Thank you very much for the feedback on this. Ultimately I built one, (a sloppy one) but it ended up being nowhere near enough for the beefy 25kg servo inrush, even with ramping algorithms and various output capacitances. I really need to get the gear to measure current with my scope so I'm not blind to current transients. I am looking into 5A ICs now.

author: mtwieg
author_rank: Frequent Contributor
timestamp: June 21, 2025, 10:04:15 pm
content: Quote from: mariush on June 21, 2025, 03:22:34 pmOh yeah if you're operating from 24V, I would select a part which can withstand at least 35V. If you intend to operate from a 24V battery, then a 28V part is probably guaranteed to fail (since a 24V battery may have >28V while charging).Quote from: jtexbox on June 21, 2025, 04:08:28 pmIs the 5.5V meant to supply some sort of controller? In principle, even if a motor is only rated for 5V, you don't need a buck converter to step down to 5V first. You can drive it via PWM directly from 24V, so long as you ensure the PWM duty cycle is limited to ~20%.