STM32f401RBT6 not connecting : Vref+ unconnected , low Vcap voltage.
Hi, I'm pretty new into microcontrollers and I have been doing recently a project using stm32f401rbt6. I have made own pcb with this mcu and have issues with connecting to it using SWD pins by using STlink. I have been investigating this problem for a while and quickly came to the conclusion that I have probably made a mistake in terms of making connections. I have connected all VDD pins to +3.3V supply and grounded all VSS pins including VSSA/Vref- pin leaving Vref+ pin floating ( I don't want to use ADC - so I thought that I didn't have to do anything with it ). I have checked all the pins with the multimeter and all VDD pins have +3.3 V . I have also checked the NRST pin ( which has an internal pull-up) and it is in high state as it should be. The BOOT pin is connected to the slide switch so it can be either +3.3V or 0. What caught my attention is that the VCAP pin is around 0.2 V - from what I have read on the internet it should be much closer to the VDD value.
I have seen a thread where a guy had a similar problem with his own project (link). His mcu also didn't work and had on VCAP only 0.4V. For him connecting Vref+ to the VDD worked.
I have looked into my datasheet again and saw that I have probably overlooked smth. The datasheet says that the Vref pins have internal VDD and VSS connections and for PCB design it should be connected like this and like this (page 109/110).
Might the fact that I left Vref+ be the cause of my problem with communicating with my mcu ( problem with starting it)? I havent seen in the document any information that these 2 pins have a crucial impact on the proper work of the rest of mcu .
Also, I am kinda confused about what I actually should do with this pin. Should I connect it to the +3.3V or connect it to the GND through the capacitor next to the Vref- pin? Would anyone have any suggestions on what should I do?
Just to clarify : pcb is manufactered.
