User Guide

CCS Technical Documentation System Module
NPM-2NX
Issue 1 07/02 ãNokia Corporation Page 25
BB component and control/IO line protection
Keyboard lines
ESD protection for keyboard signals is implemented by using Emifilter Z300 detection
The distance from the A-cover to the PWB is made longer with the spikes in the keymat.
PWB
All edges are grounded from both sides of PWB and solder mask is opened from these
areas. Target is that any ESD pulse faces ground area when entering the phone, for
example between mechanics covers.
All holes in PWB are grounded and plated through holes. Except LED holes, which can
not be grounded.
LCD
ESD protection for LCD is implemented by connecting metal frame of LCD in to ground.
Two clips are used to connect the LCD module to the engine, and those two clips are also
used to make the metal frame ground connection. Software also takes care of the LCD's
crashing in case of ESD pulse.
Microphone
Microphone's metal cover is connected to ground and there are spark gaps on PWB.
Microphone is unsymmetrical circuit, which makes it well protected against EMC.
Earpiece, buzzer and IRDA
These NPM-2NX components are protected by mechanics, this is possible because NPM-
2NX hasn't changeable A-cover.
Bottom connector lines
Table 5: Bottom connector signals with EMC protections
Bottom connector signals that have EMC protection
protection
type
VIN CHRG_
CTRL
MICP XMIC SGND XEAR MBUS FBUS_R
X/TX
ferrite bead
(600_/
100MHz)
x x x x
ferrite bead
(42_/
100MHz)
x
spark gaps x x x x x x x
PWB capaci-
tors
x x x x