STM32F427 does not boot after power on

[Bogdan]

Posted on April 26, 2018 at 17:16

Hello,

i  am using a design with a STM32F427  100pin package, and notice after leaving the board unpowered for several hours if i power up again, the software its not starting.

If i retry the restat the power it will stil not work, only after 3-4 retries. 

If i have the change to get starting  the software, then if i power off/on   it still works.

Boot1 - pin is left floating 

Boot0 pin - is tied to ground trough a 4K7 resistor

Reset pin - is tied to 3.3V trough 4k7 resistor.

Capacitors from pins 49,73  ( V_CAP) are 100nf X7R smd type

What is causing this strange behaviour?

[waclawek.jan]

Posted on April 26, 2018 at 17:35

Analog supply/ground pins not connected?

Software issue?

JW

[Tesla DeLorean]

Posted on April 26, 2018 at 20:16

Sure it is not starting?

Try adding an effective POR circuit (MCP120 type device with >100ms clamping of NRST)

Add code tight into Reset_Handler to provide signs of life immediately, before it gets stuck in loops waiting for HSE, PLL, etc to spin up.

Make sure Hard Fault reports.

[Bogdan]

Posted on April 26, 2018 at 19:10

The power supply pins are all connected,  the ground pins the same.

I am wondering if this is a software issue, since once the software starts everything seems to work perfectly.

[T J]

Posted on April 27, 2018 at 01:44

Definitely sounds like a Reset Issue.

this is my solution, I never have startup issues.

[Bogdan]

Posted on April 27, 2018 at 01:48

Honestly i work with stm32f4 as a hobby for some years now,  and never used dedicated POR ic for thss, never had such problems like this.

Also each power pin is bufferd by a 1uf tantal cap

I wil double check the resistor on the reset pin,  is there any typical value for this?

[T J]

Posted on April 27, 2018 at 02:06

Do you have a weak power supply ?

if the Vdd rail is slow to come up, this will

exacerbate

the reset issues.

Do you have a scope ?

you could trigger on the reset pulse going high, but check the rails ramping up time.

The Reset pin needs a resistor and a Cap.

You mentioned the 4k7, but you didn't mention the cap.

I use a 10k pullup and a 0.1uF on the reset pin as a minimum, but its not 100% reliable, depending on the brown out duration.

For 100% reliable startup, use the reset chip.

[AvaTar]

Posted on April 27, 2018 at 09:14

Could be a temperature-related clock problem as well.

You could try to heat it up after a long power off, before turning on.

If the startup problems are gone, I would check the clock setup and timings.

Power supply circuitry could create the same symptoms, but IMHO less likely.

[Bogdan]

Posted on April 27, 2018 at 16:27

Hello,

Bellow is a scope image,   yellow is the 3.3V supply line,  and purple is the reset pin.

The measurements where taken at 500uS/1V division.

I dont have capacitor on the reset pin

What do you think?

[T J]

Posted on April 28, 2018 at 02:06

I would say you definitely need a cap, is that 1uSec from power supply at 2.5v to Reset up ?

did you check the reference manual ?

page 29 of the F427 data sheet, VACAP has to be stable before Reset, can you check that ?

you should check pages 25-29

Page 97, NRST Pin

page 138:   You need a 0.1uF, and no resistor ??

Table 59. NRST pin characteristics shows:

Time of NRST_OUT Generated reset pulse duration Internal Reset source 20 - - μs

I can't see this 20uS running on your scope.

page 222

Appendix A Recommendations when using internal reset OFF