I'm trying to get the STM32F446 Cortex M4 microcontroller working on a board which I designed myself (I'm not an expert in this, but I'm learning). When I apply 5V through a current limiting power supply to the 3.3V LDO, the microcontroller uses all the current (max I used was 150 mA as the power supply current limit) and the power supply voltage drops to 3.1V (which means about 2.9 after the LDO), because I have the current limiter on. The power led is still burning nicely because it has 2.9V on it. So something is using up the current. When I change the current limit from 30 mA to 75 mA the power supply output voltage changes from 2.8 V to 3.1 V. When the microcontroller was unsoldered, the voltage after the LDO was nicely 3.3V and the current consumption was < 10 mA. When I added the microntroller, the capacitors and the oscillator, the current consumption goes to the limit I set on the power supply. Using an oscilloscope I measured that the input voltage isn't oscillating, also on the oscillator I don't get anything significant, there seems to be an around 10 mV random noise. The outputs of most of the pins are at 0.4V. For some reason pin 50 (JTAG JTDI) and 56 (JTAG NJTRST) are at the VCC level (2.9 V). The NRST pin was high and the BOOT0 and BOOT1 pins were low (they have a pulldown resistor). When I measure the resistance between 3.3V LDO output and GND it gives me a varying resistance (due to the capacitors) in kiloohms, if there was a short it should show a small resistance. I measured the resistance between all pins and ground and there didn't seem to be an anomaly. I was wondering if someone has experience with these microcontrollers and maybe knows that something is missing in the schematic which causes these problems? There doesn't seem to be a short and for some reason the microcontroller is sinking a lot of current. According to the datasheet (here page 83), it doesn't use more than 100 mA even when all peripherals are enabled. You can find the relevant schematic of my board in the attached pdf on the first page (ignore the motor driver and the UART to USB chip on the second page, those haven't been soldered yet). I also haven't soldered the JTAG connector or the 4 debug leds. Only the oscillator, microcontroller, LDO, PWR led, usb socket with its ESD protection, 3 buttons and the relevant capacitors/resistors.