lpcware

How to reduce effects of induced current noise caused by high in-rush?

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 18, 2016 by lpcware
Content originally posted in LPCWare by jdupre on Wed Jun 01 17:17:06 MST 2016
I am seeing problems that appear to be related to high in-rush current on wires that run under my LPC1517 based controller card.  Although the normal operating load is less than 10 amps, I am measuring very short duration peaks of up to 160 amps.  Reducing inrush by "soft-starting" the loads has shown to be a great improvement, but there are still unexplained issues with IRQ inputs and even what appears to be memory corruption when these big in-rushes happen.

1) What is the best way to deal with unused pins?  On the 1517 the are set as inputs by default.  Is configuring them as outputs with a pull down a better way to go? (My first run of boards have the unused pins pulled out to pads for experimenting...)

2) On pins that are used as inputs, is there a method to filter out induced transients with an RC network or something like that?  [ We have an off-board SPI display driver that was going crazy with this inrush until we terminated the SPI lines at the far end with a series resistor and cap to ground at the recommendation of the manufacturer.  Can a similar method be used on inputs to the CPU? ]

3) Is there something I can do with the board layout?  Currently I have:
   1 Top - Components
   2 Ground
   3 Power (an island of 3.3v under CPU, surrounded by 5V for other parts)
   4 Bottom - Signal
Would it help to bury the traces and have ground on the bottom layer that is closest to the high current wiring?

- Joe

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