Electronics > Microcontrollers

Is anything inherently wrong with thi supply circuit for stm32f103rct6?

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teslinius:
Does anything jump out immediatelly?, or with the supply circuit, because i designed a pcb with stm32f103rct6 and the uc has fried 3 times already and i have no idea why, i powered it with lab bench power supply limited to 50mA and it short circuited, i have no clue what's the problem, all the supply circuit looks fine to me, also there aren't any visible problems on the pcb, this is driving me crazy, can't figure it out, all the reference schematics i watched had same supply circuit. Only thing i notice is the reference schematic is using 100k pullup/pulldown and i'm using 10k, but i don't think that's the problem. |O

thm_w:
What voltage did you supply with the lab power supply, to where?
Did you verify it with a multimeter?
After the uC blew, did you remove it from the PCB, and then power on the power supply and measure what voltage it receives?
Anything externally connected?

bugnate:
Agree with previous poster than you need to provide a lot more debugging info if you are hoping for any help. That said, as far as "jumps out at me", and without hearing your side of things... You might reflect on Q11 being an NMOS part on the high-side. Likewise L3 and L4 may not be a good idea. I'd short all of them out and see what happens.

DavidAlfa:
This looks very wrong, I've never seen anything like this before!


Where did you saw that or got the idea from?
Normally you add capacitors to the LDO output, put the series inductor and then more capacitors.
The LDO output must always have direct connection to a capacitor!
But like that, the output has a high impedance path when dealing with transients, there's no capacitor to properly filter the changes, but a coil that will block these fast current spikes, causing the ldo to do very weird things, or even charge up and oscillate, creating a LC tank circuit.

As they said, short them out and try again.
This is the usual way of using a filtering inductor:

T3sl4co1l:
Only one side of the transformer is fused.

It's a 18VCT transformer, right?

Why ferrite bead supply the MCU?  Do you know you'll need extra filtering between, whatever else is on +3.3V?  Or filtering to, as the case may be?  It can be better without, as the supply is bypassed by everything connected to it.  This is more helpful on 4+ layer inner-plane PCB designs, but doesn't make much difference on 2-layer designs with only stitched ground fill (where +3.3V has to be routed as just any other trace, and so there isn't direct communication between bypass caps on the supply).

As above, large inductors on linear regulators, is just wrong.  Easy fix.

If you're going to the trouble of burning three separate MCUs, why not consider probing the supply voltage with an oscilloscope while you blow one of them?  Set it to rising trigger, 2.5V threshold, single shot acquisition, scales around 1ms/div and 1V/div, and see what's happening.  As thm said, this is probably better done without an MCU (and other chips for that matter) installed, so you aren't burning up your supply of parts...

Tim

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