Power and STM32s

[Yahya Asl Soleimani]

Posted on March 13, 2017 at 09:08

Hello

Our team is using STM32F103R8T6 and STM32F405R8T6 for a robot and for some reason sometimes when we turn the power on (from battery or a DC power Supply) the MCUs short from the inside and when we change the header board for the MCUs which we designed ourselves, everything is fine. 

here is the schematics for our power supply.

we have also used coupling capacitors as recommended in STM32 datasheets.

What do you suggest? is there anything we have missed?

if anymore information is needed, i'd be happy to provide.

[Nor Sch]

Posted on March 15, 2017 at 14:36

Don't know how you connected all the needed Stuff (Power-Pins of MCU with some 10nF and 100nF Capacitors, nReset-Pin). But you should look with an Oscilloscope on these Pins. Is your Power-Supply stable? Is the Reset-Pin fine?

[Tesla DeLorean]

Posted on March 15, 2017 at 15:11

Unfortunately you need to take a more systemic view, large voltages/currents can be introduced through a variety of routes, and back into the supplies. Review the whole design looking for potential to violate the 'absolute maximum' limits on all pins, especially those controlling motors, relays, etc where large reverse emf pulses might occur, or large voltage/current spikes.

Consider if you need more protection on IO pins.

[AvaTar]

Posted on March 15, 2017 at 16:23

I'd agree with this assessment.

Either you violate some power supply related requirements (perhaps temporarily injecting voltages on GPIOs before Vcc is stable), or you have EMI issues with attached inductive components.

[Dvorak.Peter]

Posted on March 15, 2017 at 22:05

'MCUs short from the inside' sounds a lot like SCR latchup.  

This is caused by injecting IO pins with voltage outside of power pins.

Peter

https://www.google.ca/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiB777CtNnSAhUL0oMKHUFsC_kQFggcMAA&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FLatch-up&usg=AFQjCNE-HdMNajzhUYFSu10djzVHNxiljw&sig2=tF_EMpcxfId5Mf5NHjPLcg

https://community.st.com/external-link.jspa?url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FLatch-up

https://www.google.ca/search?q=SCR+latchup&oq=SCR+latchup&aqs=chrome..69i57&sourceid=chrome&ie=UTF-8

1. https://webcache.googleusercontent.com/search?q=cache:1CZTHJycFTMJ:https://en.wikipedia.org/wiki/Latch-up+&cd=1&hl=en&ct=clnk&gl=ca

2. https://www.google.ca/search?q=related:https://en.wikipedia.org/wiki/Latch-up+SCR+latchup&tbo=1&sa=X&ved=0ahUKEwiB777CtNnSAhUL0oMKHUFsC_kQHwggMAA

[T J]

Posted on March 16, 2017 at 01:20

I think you are getting ground spikes when the switch is bouncing.

i try to use inrush current protection into a larger capacitance, I dont have any trouble.

eg, after the switch before the 5V switcher

but you may feel this is going overboard.

[Yahya Asl Soleimani]

Posted on March 16, 2017 at 11:07

thank you I think this may be it we are monitoring all the voltages to see what's what

[AvaTar]

Posted on March 16, 2017 at 12:07

Older CMOS chips, AFAIK, tended to 'latch-up' at about 15V. Not sure about ST's technology.

However, that seems to point to external, inductive sources (motor coils, switched supplies).