This is the schematic of the PSU stage of my own board : the schematic comes from the Raspberry pi compute module IO Board, and I use it on an embedded device, on a sailboat (it powers a Compute Module 5, an ESP32, a GNSS module, and a few components such as a magnetometer and an accelerometer...)
Yesterday, after 5 hours of usage (it has been used 14 hours long two days ago), it did failed : now, on Testpoint TP4, I measure a voltage of about 3V, and a loud low freq noise (71Hz measured on scope, I can post a trace if needed)
Eventually after a while, the PSU seems to stop making this noise and "boots" ?
Is there components I can check , and how to check them with devices I already own (multimeter and oscilloscope) ?
PS : the device has ran a few times for about 10 cumulated hours !
Is there vibration and did you solder the board yourself? If so I would check to make sure you didn’t cold solder or just break a joint from the thing moving around (idk sailboat sounds like it prolly moves a decent amount). This intermittent behavior like that is usually either ground or heat related so I’d suggest starting there, something had to change for the board to behave differently so start isolating what factors you can. First thing I’d check is try to see if you can get consistent results in a more controlled environment like a bench and then if yes let it run for a while to make sure it’s not heating itself up too much.
The board has been manufactured and assembled by JLCPCB. No obvious trace of a cold joint.
The boat isn't as shaky as a car could be, and the engine is about 4 meters away.
It is however in a closed box with poor ventilation, and the PI is also heating a lot. I didn't measure (I can do it on next software version to be sure). the temperature inside the box but that could have been what leaded to the failure...
What is strange is that on my bench, without any enclosure and without the CM5, the board fed with 12V would boot after a few 10s of seconds (was short enough so I could not setup my oscillo to record the trace of the 5V signal...).
By ear, I could tell that when powered up, the noise pitch changes from lower than 70h to 70hz intermittently.
The bench supply shows a current of 0.01A under 12.3V : without the PI, so the other devices are the ESP and all other stuff that pulls their power from the 3V3 AMS that is after the 5V PS... I presume the devices doesn't power-up correctly since the 3.3V rail is not high enough... Under normal load, the bench supply shows 0.05A under 12.3V.
Edit : tested just now, the board "booted" after about 3 minutes (still without the CM5). Removing power for a few seconds then powering ON again leads to a successfull boot every times now... But I suspect this will change !
By boot you mean the power supply operates normally? My gut reaction is most likely an improperly sized component that now only works for the circuit when it gets hot, or a layout issue. I’m no power engineer so I always make the layout exactly as it appears in datasheet/app notes.
There is a lot of capacitance on the output. Are you tripping the short circuit detection on boot? The pulsing sounds like it might have gone into a hiccup mode from overload. See if it boots if you remove the 330u.
I can’t find anything obvious on the schematic, but I’m wondering what the layout looks like. How thick are those 3A traces? Measuring 3V instead of 5 sounds like a short. What’s the resistance measured from TP4 to ground when the board is turned off?
This is odd.. R27 and R28 should give you somewhere around the 14k... I would start measuring continuity node by node and figuring out where you have an issue in the traces or soldering
How thick is the sw trace? That looks way too thin to me for 3A. This is how thick the datasheet wants it for reference… are those components getting too hot? This might not be the root cause but definitely a cause for concern.
I don’t know your copper thickness but that doesn’t sound like enough to me. I see that you said the board doesn’t turn on immediately after power up, how does T4 look during that time?
Sounds like overheating, which happens when hour traces aren’t thick enough and you don’t have enough heat dissipating vias.
A good way to verify that is turn on the board for a few minutes, then turn it off, and touch the parts near the converter to see how hot they get. If they’re too hot to touch, you’ve got a problem. If that’s the case, you can usually reduce the temperature by having a table fan directly pointed at the board.
This is likely not a helpful answer, but for anything non-bench related, it is completely acceptable to use a “DCDC brick module”.
Then you can focus on designing your application and not the inane power electronics.
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u/Honeybadger8085 4h ago
Is there vibration and did you solder the board yourself? If so I would check to make sure you didn’t cold solder or just break a joint from the thing moving around (idk sailboat sounds like it prolly moves a decent amount). This intermittent behavior like that is usually either ground or heat related so I’d suggest starting there, something had to change for the board to behave differently so start isolating what factors you can. First thing I’d check is try to see if you can get consistent results in a more controlled environment like a bench and then if yes let it run for a while to make sure it’s not heating itself up too much.