OSHW LM22676MR-5 DC_DC_Module Review/Feedback - Page 1
Forum section: electronics / general

author: Davon322
author_rank: Newbie
timestamp: July 07, 2025, 11:30:17 am
content: Hi All,I've been messing about designing a wide input DC-DC converter, trying to get back into design work and wanted to get some feedback on this,I have ordered the board from JLCPCB and the parts from Mouser to build it up and test it. in the mean time please see attached schematics, BOM and layout.Spec is quite vague as I'm learning as I go along with this Ti part.6-36VDC in5V 2A outI'm planning on making a info page on how this experiment and what I learnt from this project/process.any feedback much appreciated.Regards,D

author: Swake
author_rank: Frequent Contributor
timestamp: July 08, 2025, 05:33:40 pm
content: Input protection: yeah !Mounting holes are grounded. It is a choice but I wouldn't do it unless there is a specific need, but again it is a choice.Input and output are GND connected, this means there is no isolation when using several of these. Does not matter if you don't care about such a feature of course.The regulator is a 3A version, why are you limiting to 2A?Is the pad big enough too cool the chip? Might put a field of vias there.Nice big components that are still hand solderable but SMD nevertheless. The diode might be somewhat small.My personal choice for test points (when real estate permits) is to us 2 pads, 2.54mm apart, header style. It is more flexible. When I'm not using a jumper wire I usually end up soldering a high bridge wire allowing clamping probes. You're using those beads, I feel these are bigger and always out of stock when I need some. Even on full SMD boards I prefer drilled test points as the hole avoid slipping with the probe.I cannot comment on the implementation as I have no experience with this chip.You could make a 3 legged 7805 replacement with this. And other voltages and a variable voltage one if the chip comes in these configurations.Curious about your measurements on stability, rise time, ripple. Temperature influence. Push it to and over its limits. Give it a dirty input. Overloading and more. challenge the spec sheet

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 10, 2025, 09:56:13 am
content: You need to limit the gate voltage on Q1, or else the FET will be destroyed when the input voltage gets above (almost always) 20V. You can do this by for example replacing D2 with a 12V zener.The single row headers for the input and output voltages are quite flimsy. Modules like this are usually made in two different versions. Some are made as a module to be soldered onto a bigger PCB. Other modules are made to be mounded elsewhere and then have mounting holes, but also have bigger / stronger (screw) connectors.Schematic has been drawn properly and neatly, with "signal" flow from left to right and voltages from top to bottom. Except for J1 and J2. Why did you not just draw them on the input and output of the schematic?It has advantages to make the enable pin accessible from the outside. This allows the module to be turned on and off by an external source (switch, microcontroller). But the input is pretty high impedance, ans thus susceptible to picking up noise, and a long unterminated track is not good here, but adding a test point close to the pin is nice, and costs nothing.Maybe add a resistor to GND also for the enable pin. This generates an option to turn the output on/off, depending on the input voltage. It costs nothing to just add a footprint, and it does not have to be populated if the function is not needed.I would also remove the thermal reliefs from the mounting holes. This helps preventing the copper from getting loose if the screws are tightened (too much), and also remove the thermal reliefs from the output pin U1 (I.e. U1, L1, D3). This net very easily generates a lot of EMI, and the smaller it is the better.L1 is quite small. Have you verified it's big enough so it won't saturate? (I have not verified it).

author: Doctorandus_P
author_rank: Super Contributor
timestamp: July 10, 2025, 11:45:10 am
content: Also: (Separate sub topic).I also wanted to design a few modules like this, but I was unpleasantly surprised by the prices of (western) SMPS IC's in SOIC packages. The IC you choose costs over EUR 4 (one up) and this is completely out of proportion with it's smaller brothers and sisters. I searched for this thread again, because I happened to look up the price of an TLV62569APDRLR This one is 20ct (one up) and 9ct (1000+). This one only has a quite low input voltage (only 5V5) but there are very many small SMPS IC's in small packages that can have a higher input voltage.The vast majority of applications these days is to create a low voltage rails for some microcontroller, and 100mA or thereabouts is often plenty, and these small chips can often already deliver > 1A, and that puts the SOIC chips in a quite small niche, with the "high current with external switches" circuits on the other end of the spectrum.

author: Davon322
author_rank: Newbie
timestamp: July 10, 2025, 02:01:28 pm
content: Thank you Doctorandus_P & Swake for the constructive feedback.- Good point on the grounded mounting holes I usually do this to easily attach my test probes but with the a dedicated test pins its kind of pointless (bad habit).- Isolating the GND path could be a good option for the next revision.- Regarding the Vripple please see attached PDF with calculations.- The Inductors Isat is 4A, this circuit is designed for a 2A load and a Iripple of 300mA.- Good point external option to control the enable pin will be added on the next revision.Once I receive the board and components I'll build it up, test it and share my findings.

author: Davon322
author_rank: Newbie
timestamp: July 11, 2025, 04:33:20 pm
content: Got the PCB assembled this morning (it worked first time... usually skeptical if this happens) and did initial testing with a 200mA load. see attached soft start waveform, I have ordered a Variable DC Load should be here over the weekend to do full load testing. The 5V output doesn't stabilise until the Input reaches 6.15V.

author: Swake
author_rank: Frequent Contributor
timestamp: July 11, 2025, 05:19:14 pm
content: Good job making it work the first timeNearly no difference between the 2 input voltages, but what a bumpy start up!No overshoot, that is pretty important as it can fry sensitive electronics quickly.Now I wonder how other shoppers and the good old 7805 behave at start-up with a similar load.

author: Davon322
author_rank: Newbie
timestamp: July 15, 2025, 05:22:52 pm
content: Please see attached Load test results, I haven't analyzed these yet, but have learnt more about the heat dissipation on the DC-DC and Inductor is getting HOT!!!

author: Swake
author_rank: Frequent Contributor
timestamp: July 16, 2025, 06:58:05 am
content: From your measurements 6 V input is too low. It does not reach the 5 V output. See in the datasheet bottom of page 12 - equation 9. Sorry, I'm too lazy to calculate this, I cherish the good old times when 78xx regulators were used and we didn't really care much about the consumption of a device200 mV lowest ripple is high. With 520 mV ripple it clearly doesn't like outputting 1.8 A at 12 V. You'll not be able to feed a digital circuit reliably with this. Unless.... the variable load is the culprit here. It probably is some switching device too.You might want to use simple resistors as load to verify. Something like this:https://www.aliexpress.com/item/1005007944100493.htmlor like thishttps://www.aliexpress.com/item/1005008120557924.htmlWhat 'thing' have you used to generate the input voltage? If it is anything else than a battery or a very stable and reputable lab power supply then it will also have some influence on the results.Please upload pictures directly as images, not zipped files, this makes life soo much more easy.

author: Davon322
author_rank: Newbie
timestamp: July 21, 2025, 09:59:45 pm
content: Hi All,Regarding the output ripple I have noticed that it was relaying onto the Input which made me investiage the DC supply I verified it was not the supply by swapping it out for a 12V Lead Acid Battery,seeing the same ripple as before on both sides was a first for me... I played about swapping in and out various combinations of capacitors I found that 100uF Electroytic on the output smoothed both the inputand output ripple. the worst ripple seen before adding this was approx 500mV, with the addition of this capacitor the worst scenario a mixture of voltages and loads was 50mV a great improvement.I verified the RPP part of the circuit with good results. I have decided to reduce the size of the TVS diode and RPP FET for footprint reasons.I have relaid the PCB into a standard footprint of a 1/16th DOSA BrickI noticed during my testing that the LM22676 and the Inductor seemed to get rather hot when being on for a long period of time I have accounted for this in the new layout... hopefully will help with this.Please see attached Rev A1. Thanks for the help so far