Content originally posted in LPCWare by bavarian on Wed Dec 03 06:32:43 MST 2014
You can't really avoid these effect on systems running with high speed signals. You can only try to limit them to an acceptable level.
A generic microcontroller is always a compromise between performance and price, any focus on specific aspects will either increase the price or limit the performance on another part of the system. Or both.
As we are not going to change the system and increase the price 8-) , you need to try the second option: limit the coupling effects.
For noise on the power supply domains:
[list]
[*] Use more than one decoupling capacitor on each pin to reduce ESR
[*] Use filter circuits to get rid of specific frequencies
[/list]
For crosstalking problems and frequency related problems
[list]
[*] Reduce the on-chip frequencies as much as you can. There is no need to run the CPU on 204MHz if you only need a 120MHz performance
[*] Reduce the current consumption of the MCU by switching off all blocks which are not needed
[*] Take care of the routing of the high speed signals (for example EMC) on the PCB
[*] Implement series resistors in the EMC signals (and maybe other fast digital interfaces) to reduce frequency responses
[*] Don't configure pins to high speed mode if not really required
[/list]
Another quite tricky hint: in the LPC4350 LQFP package definitions you can see on which side of the silicon die the AD converter(s) are located. The signals nearby the AD pins are the most suspicious to couple "noise" into the analog ports. On the BGA package these suspicious pins can normally also be founded in the same section of the chip, also the bondwires from the die to the ball locations are structures the same way. So, if you can, try to avoid using these pins by finding the required function on another pin (if available).
Regards,
NXP Support Team
