Hello,
I'm trying to use LPC4370FET256 (BGA) device with HSADC for continuous sampling of 4 analog channels with 1MSamples / per seconds (each). While all things regarding data transfer has been successfully managed, I'm struggling now with power supply (VDDIO:3.3V) noise coupling directly into HSADC samples.
My questions are following:
I wish I was wrong, but form my observation, it looks, that HSADC is supplied from digital power supply, and is very prone to digital power supply noise, and this make him practically unusable for some serious applications, as it's almost impossible to protect digital power supply form noise.
Regards,
Irvin
Dear Irvin:
Could you share with us on your experience to use LPC4370 for HSADC and external SDRAM? If the LPC-Link2 comes with a lot of external SDRAM, then it would be very useful.
Hi Irvin,
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.
For noise on the power supply domains:
- Use more than one decoupling capacitor on each pin to reduce ESR
- Use filter circuits to get rid of specific frequencies
For crosstalking problems and frequency related problems
- 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
Another quite tricky hint: in the 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).
Hope it helps!
Best Regards,
Carlos Mendoza
Technical Support Engineer