[Solved] Getting desperate with my faulty custom stm32f4 board

[pierre23]

Posted on August 19, 2015 at 20:18

Hello,

I made a PCB with a STM32F429IGT6 (f429 176 pins) and I want to test it but... I cannot flash my stm. I've tried many things and I'm started to think I might have missed something so if some experienced stm32f4 users could take a look at my stuff and tell me if anything's wrong that would be pretty awesome.

Here are some details about my board.

I soldered everything myself but tested many pins and there is no evidence of shorts or whatever. Everything seems fine on the PCB.

I have connected my stm32 to the st link device this way:

 - VCC and GND of course

 - SWCLK on SYS_JTCK-SWCLK (137/PA14)

 - SWDIO on SYS_JTMS-SWDIO (127/PA13)

 - TRACESWO on SYS_JTDO-SWO (161/PB13)

 - NRST on NRST (31) [NB: there's no pull and no pull down on NRST].

About the �C, I have more or less copied the stm32f429i-disco schematics (see below).

Hence, there are:

- 100 nF capacitors on every VDD

- 1.1 uF caps on VDDA and VREF+ with a bead between the caps and VDD

- 1 uF cap at VBAT (+ connection to VDD)

- PDR_ON is connected to VDD

- VCAP1 and VCAP2 are connected to GND with 2.2 uF caps.

All caps are very close to the stm.

Also:

- BOOT0 is connected to GND.

Something important: after powering the board (which delivers a 3.3V signal to the stm), I noticed that both VCAP1 and VCAP2 were at 0V, although I've read somewhere they shouldn't be. All other pins (Vdd, Vbat, etc) have a correct voltage.

Finally, when I try to connect to the �C, st-link tells me ''Can not connect to target!''. I've tried normal and ''connect under reset'' modes (SWD) but nothing works.

Does anybody know what could be wrong?

Many thanks,

Pierre.

#stm32f4-flash-error

[stm32forum]

Posted on August 19, 2015 at 20:35

Don't see the BYPASS_REG pin (pin 48) in you schematic, where is it connected to?

Vcap1 is not pin 71 but 81.

Vcap2 is not pin 106 but 125.

Vref is not pin 32......

Check the rest yourself or post the used schematic.

[pierre23]

Posted on August 19, 2015 at 20:40

Right, sorry, I left Bypass floating. Should I connect it to something?

The piece of schematics you see is extracted from the stm32f429-disco schematics, hence the pin numbers are not correct (but they are correct on my board of course).

[Tesla DeLorean]

Posted on August 19, 2015 at 21:12

Both VCAP pins should be outputting 1.25V, if they are not the internal regulator is not functioning, or you have the part orientated incorrectly.

Without the 1.25V running the core, nothing is going to talk to you or function on the device.

[Tesla DeLorean]

Posted on August 19, 2015 at 21:18

BYPASS_REG should be grounded.

[pierre23]

Posted on August 19, 2015 at 21:42

I'm 99.99% sure my stm is orientated correctly (I double checked just in case).

Ohhhh I'll try to put BYPASS_REG to GND asap and keep you posted (I can't until tomorrow, damn).

''On packages embedding the BYPASS_REG pin, the regulator is enabled by holding BYPASS_REG low.'' How the hell did I miss that... Anyway thanks and see you later!

[pierre23]

Posted on August 20, 2015 at 12:24

It works!! I knew I had missed something...

You can see my crappy solution here hehe:

Anyway thanks a lot everybody. I'll set the thread as solved.