FM0+, FM3 & FM4 MCU

[Anonymous]

I'm using the FM3 MCU MB9BF516N for several PCBs.

I have now some PCBs not working.

It seems that the MCU does not start, because I also get no connection with the Debugger using SWD.

What could be the reason?

In the datasheet I found in chapter 12.4.7 Power-on Reset Timing the following:

Power ramp rate dV/dt (Vcc: 0.2V to 2.7V) Min 0.8 mV/µs, Max: 1000 mV/µs

Is this a condition for proper startup of the MCU?

In other words: If the power Ramp on Vcc is slower than 0.8 mV/µs, could startup of the CPU fail?

[ShipingW_81 · Accepted solution]

Yes, it's possible the reason.

Please follow the power-on reset timing spec on Vcc ramp rate, and then let me know if it helps.

[Anonymous]

Yes it's the reason. but I'll use now an microcontroller supervisory circuit for external reset signal to ensure proper startup