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| MCU - 100nf cap to GND before and/or after the inductor AVCC pin |
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| Psi:
OK, i did some tests, Seems the issue isn't right at switch-on. It's when the MCU timer generates 6khz signal to drive the power on piezo beep. Looks like the 6khz current spikes from driving the piezo maybe causing the inductor to kickback. I'm seeing up to 5.75V on the AVCC pin to GND, but all the other VCC to GND caps on MCU are fine so it's just an AVCC issue. (I'm probing using the spring clip right on GND at the MCU). |
| Psi:
Yep, I just replaced the inductor with 22R resistor. No more overvoltage. Looks like I do have a separate issue with the piezo circuit, it should not be pulling down the 5V rail like that. But at least it proves the overvoltage part of the problem was the 10uH inductor. So something to keep in mind. If you follow the datasheet recommendation of a 100nF cap to GND on AVCC and a 10uH inductor to VCC. Then you run the risk of killing the MCU if your 100nF cap goes open circuit and you have any high frequency noise on the supply rail. |
| T3sl4co1l:
You didn't zoom on the negative spike / ripple? :-\ Tim |
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