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STM32F446 VCAP/NRST low on custom PCB, can't program


Hello Community,

i am trying to program an STM32F446 on a custom PCB but i am failing to do so:

Info : Target voltage: 3.324064

Error: init mode failed (unable to connect to the target)

In my search for the error i found my VCAP1 to be around 0.2V and VCAP2 to be 0.6V, according to the RM these should both be 1.2V. I'm trying to find the reason for that. The NRST is also at 0.15V. I assume the NRST is permanently low because the VCAPs are low.

As for my PCB im using the STM32F446ZET6 LQFP144, the schematic is based on the HW Design manual (AN4488). A stable 3.3VDC is applied to VDD, VDDA. Ground connection is present, there are no Copper islands. PDR_ON is connected to 3V3. There is no external Pull-Up on the NRST, just a 100nF cap close to the STM. The STM is aligned correctly (Pin1 is in the correct location). Boot0 and Boot1 are both tied to GND, i have tried to pull up Boot0 to 3V3, no change.

This is the third STM32F446 on the Board, i am about to populate another board to rule out any PCB manufacturing issues.

I am happy about any hints. I am also still new to microcontrollers and PCB design, so major (design) mistakes are definitely possible.

I attached the supply part of the schematic. Don't mind Boot1 floating, i've grounded it with a wire in the final design. VCAP1 and VCAP2 are also no longer connected in the final design.




Something is terribly wrong.

Check chip orientation.

Go though all VDD/VSS pins with a continuity tester/ohmmeter and check whether they are connected as supposed, and whether they are not shorted to neighbouring pin or ground. Measure directly on the pins.



Does the 144 pin package have "dot"​ on two corners? The smaller 64pin package does have smaller and bigger dot, and when the text is oriented correctly there should be other of the dots at bottom left corner, that's the pin 1 marker.

It's not once i have soldered the chip 180 degrees rotated when in hurry...​

Associate III

Any Update on this matter? I'm struggling with the exact same issue but on an STM32F405.. did you manage to fix this sir?

I'd hope so FOUR YEARS later...

Illustrate YOUR problem, and let's solve THAT

Lead with a Schematic, and images of part/board as placed. Something high resolution and in-focus

As Jan points out this is likely to be a pretty gross fault, like the orientation of the part is entirely wrong / rotated.

NRST Low is indicative of VDDA/VSSA not being connected. Use of analogue ADC/DAC is irrelevant, and analogue also used for other things, including the POR circuits.

VCAP, single pin 4u7 F cap, two pins 2u2F on each. Should be 1.25V, none suggests part placed wrong.

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