Wrong value of VCAP capacitors in STM32F407VGT board

[LMI2]

I have 10uF (=10uF+100nF)ceramic capacitors for VCAPs in a custom board. Voltage there is 2.7V. Supply voltage is 3.3V

I have problems getting the STlink to accept the board. First I managed to erase the chip, now STLink does not even recognise the chip. A dead CPU already?

Are 2.2uFs really needed, I try keep number of stored values here as small as possible.

[waclawek.jan · Accepted solution]

While the DS is very specific with the 2.2uF, and while some LDO are known to oscillate with higher than specified capacitive load, 10uF doesn't sound to be too far.

Grounds correctly connected to all pins (checked and double-checked by measurement)? Decoupling close to the pins? No excessive voltage or oscillation on 3.3V pins? No >7V on any other pin? No oscillation on VCAPs?

JW

[T J]

I checked my F417 custom board,

one 2.2uFs only on each of those pins, Both reading ~1.31V

[Tesla DeLorean]

Should have 1.25V, expect other issues on board

[LMI2]

Thank you for info. I have tried to check those connections but it is hard when chip is this dense.

I wonder about that 2.7V VCAP voltage. "No oscillation on VCAPs?" I haven't checked with a scope but the voltage looks stable.

Power comes from 7805 type 3.3V switching regulator. Every CPU + pin has 100nF and most have also a 10uF a little further eway. And there are other capacitors between + and ground. This is a test board so I have room.

I have to check further, swapping CPUs is hard I hope it is not that.

[LMI2]

I resoldered all the CPU leads and it helped. Keil does not detect the board but ST link does. I can download a program but it looks like it is not running. More work.

Edit: And the Vcap voltage is now 1.26V

[LMI2]

And it works.

I had to toggle the LED pin and not something else to get it blinking.

And with 10uF Vcaps

[waclawek.jan]

Please mark it as solved.

[LMI2]

Like that?

[waclawek.jan]

Yes thanks.

This forum is horrible in keeping track in what thread did I (or others) start conversation, and this helps at least a little bit to filter out those which don't need attention anymore.

JW