STM32F407's Clock is not working

[rui CHU]

Posted on March 14, 2017 at 12:31

dear. Engineer sir

We are currently working on a project using the STM32F407ie UFBGA176 chip.

After configuring the microcontroller on the PCB and checking the operation of the microcontroller, the external oscillator clock will not work.

We have confirmed that there is no problem with the power pin and reset circuit.

So I checked the circuit and found that nothing was connected to the BYPASS_REG and PDR_ON pins.

In our current PCB, there is no way to connect these two pins because BYPASS_REG pin and PDR_ON pin are not exposed.

What is the default value when nothing is connected to the BYPASS_REG and PDR_ON pins?

When I looked at the data sheet, I noticed that the VCAP_1 and VCAP_2 pins were connected to the out portion of the regulator.

Is it possible to connect from outside through this part?

Or if there is a way to run the clock without using the BYPASS REG and PDR_ON pins

What is the reset controller associated with the PDR_ON pin?

And if there is a way we do not know except for the above method, I would appreciate if you could suggest it. please

Thank you

[Tesla DeLorean]

Posted on March 14, 2017 at 14:47

You need to turn the HSE on in your own code, it does not turn on automatically. Can you download and debug code in your part?

[rui CHU]

Posted on March 15, 2017 at 03:51

thank you  for your reply

but stmf407IE has no external oscillator.

So debugging port does not connect It seems that The hardware problem must be solved first.

[Tesla DeLorean]

Posted on March 15, 2017 at 05:39

Ok, I'm confused, you initially said the external oscillator wasn't working, now that it has no external oscillator. Which is it?

I wouldn't expect the external oscillator to start, it is not need for the part to function, so you can't use it as a sign-of-life.

Doesn't the Data Sheet go over the BYPASS_REG and PDR_ON?

What voltage do you see on the VCAP pins, and NRST?

My expectation is BYPASS_REG normally floats high, and the regulators will be off. You'd likely need to provide 1.25V at the VCAP pins.

[rui CHU]

Posted on March 16, 2017 at 06:13

sorry i made mistake.

I wanted to say that there is no internal oscillator.

I have read the data sheet, but stm32 is bga type, so the pins are not shown on pcb board. So I can not do anything to BYPASS_REG and PDR_ON.

There are our Vcap and NRST Circuit. 

I tried with your advice. provide 1.25V but It still does not work.

Is there any other way?

[Tesla DeLorean]

Posted on March 16, 2017 at 09:43

It is usually a good plan to escape pins you don't understand to test points when using BGA parts for the first time.

I would suggest reviewing the schematic of a working design, like the EVAL board, both as a design and functional reference. 

The core needs to be powered, and not held in reset. One of my signs of life test is to use the System Loader via USART or USB. 

Discuss with the FAE assigned to your business account.