(All-in-one DC-DC Buck converter) MPM3630 burns at startup. Layout error? - Page 1
Forum section: electronics / projects

author: alirabarber
author_rank: Newbie
timestamp: June 01, 2024, 10:53:21 am
content: Hi,I am struggling with a working layout for the MPM3630 from MPS.The input voltage is 16 V (4S LiPo Battery) and the desired output voltage is 6 V.There is no load connected.When I connect VCC it works fine at first.However, when I try disconnecting and reconnecting the Battery multiple times, then eventually the MPM3630 burns at the VIN pin.I am relatively sure that the internal MOSFET power stage burns.It actually lights up and burns really beautifully.I did the same experiment with the corresponding Eval-Board: It works fine.Also with additional input capacitance as I have it in my design.So, I am pretty sure, that I have made a significant layout error.But I cannot seem to find it.And I am quite lost about what is actually happening here and causing this fail.Does anyone have a hint as to what might be the error, or what is happening here?I attached screenshots of my design and a picture of the burned circuit.Thanks!Alex

author: Psi
author_rank: Super Contributor
timestamp: June 01, 2024, 11:20:35 am
content: Putting 16.8V (4.2*4) into an 18V switchmode chip is playing it way to close.Switchmode converters can generate a lot of ringing/noise. And you only have 1.2V before it's at 18V.See if you get the issue with a 3S lipo

author: alirabarber
author_rank: Newbie
timestamp: June 01, 2024, 11:41:47 am
content: That's a good hint, thanks!The actual ringing should not be influenced by the board layout, correct?I thought, that the entire commutation loop of the power stage was inside the package.I can imagine, that the actual U_DS_max voltages of the MOSFETs vary from part to part.In that case, the eval board would have a "lucky" part.What could have an influence, is the different cable length to the battery between the two setups.The eval board setup has a significantly longer cable length.It is a much bigger board and I did not solder the cables to it.I will repeat the experiment with a 3S battery.

author: Phoenix
author_rank: Frequent Contributor
timestamp: June 01, 2024, 12:00:28 pm
content: Quote from: alirabarber on June 01, 2024, 10:53:21 amThis might be causing lots of arcing and voltage spiking.

author: alirabarber
author_rank: Newbie
timestamp: June 01, 2024, 12:45:42 pm
content: I just tried it again, first with 2S and then with 3S.It works fine.The ringing as explanation makes sense for me.It seems, that the eval-board layout somehow works better to suppress ringing than my layout.I suppose the big VCC and GND areas can have something to do with it.When I connect and disconnect VCC multiple times, there are for sure a lot of arcs and current spikes.I am not completely sure about voltage spikes - because of the input capacitors.To solve the issue I will limit the max voltage of VCC to a 3S LiPo.If anyone has ideas on how to reduce the ringing, I am open for suggestions.Other than that I consider the problem as solved and am really relieved.Thanks for your time and effort!

author: RiZsho
author_rank: Contributor
timestamp: June 01, 2024, 04:46:07 pm
content: Hi!Voltage ringing on input destroying DC DC converters is nothing new and limited to this chip only. I know LT had an app not, but can't remember the title. The jist of it is the following: Long leads on input can have some inductance to them, so when you connect them to the input of the DC DC they tend to form a LC tank with the input caps (low esr helps ringing a lot in this case) and can cause massive spikes upon connecting. The app note tested three configurations: only ceramic, ceramic+electrolytic and finally ceramic+RC snubber in paralell (1uF||4.7Ohm). Basically keeping the ringing damped by increasing series resistance seen on empty caps. Almost all solutions helped a lot in some form or other ie. lowering the spike significantly.Hope this helps

author: mikerj
author_rank: Super Contributor
timestamp: June 01, 2024, 04:59:53 pm
content: This is a classic failure mode caused by the ceramic decoupling capacitors on the input to your circuit. Have a look at this application note:https://www.analog.com/media/en/technical-documentation/application-notes/an88f.pdf

author: RiZsho
author_rank: Contributor
timestamp: June 01, 2024, 06:23:11 pm
content: That's the one!

author: alirabarber
author_rank: Newbie
timestamp: June 01, 2024, 07:56:48 pm
content: Oh, very cool!That definitely helps!Now that I think about it, it absolutely makes sense.I will take a minute and read it in detail.Thanks alot!