Lasse Madsen

Reset_b pin oscillating - MK40

Discussion created by Lasse Madsen on Sep 19, 2012
Latest reply on Jul 24, 2017 by Mayra Ramirez

Hi All,


I have two new boards I just build with the MK40.


I measure 3.3V on all power pins powered from an LM1117-3V3 together with 5V on the VREG pin from a LM1117-5.0V regulator.


Both chips are brand new and both exhibits square wave oscillation on the RESET_b pin and I have never managed to program them.


My debugger (UlinkPRO) can connect to the parts alright however I cannot flash any of them without getting a memory error.


I've read on this forum that other people have seen the same problem but I cannot seem to find a cure.


I have lots of decoupling capacitors (1nF // 100pF // 100nF so forth) around the chip as well as good electrolytes which ensures literally no ripple voltage on my supplies (i've tried removing the electrolytes as well to give a faster ramp up on the psu without effect)


I have tried an external 2.5V reset monitor tied directly to the Reset_b pin without luck


I have tried powering the chip via it's own 3.3V regulator (by hacking my pcb) this did not help either


Holding Reset_b low a few seconds while powering up and then releasing it doesnt do anything either so it doesnt seem to be related to POR ramping


Any ideas !?