User Guide

CC Technical Documentation System Module
NPM-10 (3595)
Issue 2 03/2004 ©2004 Nokia Corporation Confidential Page 19
The operation of the charging circuit has been specified in such a way as to limit the
power dissipation across the charge switch and to ensure safe operation in all modes.
Figure 2: UEM charging circuitry
Charger Detection
Connecting a charger creates voltage on VCHAR input of the UEM. When VCHAR input
voltage level is detected to rise above VCH
DET+
threshold by UEM charging starts.
VCHARDET signal is generated to indicate the presence of the charger for the SW.
The charger identification/acceptance is controlled by EM SW.
The charger recognition is initiated when the EM SW receives a “charger connected”
interrupt. The algorithm basically consists of the following steps:
1. Check that the charger output (voltage and current) is within safety limits.
2. Identify the charger.
3. Check that the charger is within the charger window.
If the charger is accepted and identified, the appropriate charging algorithm is initiated.
Charge Control
In active mode, charging is controlled by the digital portion of the UEM. Charging volt-
age and current monitoring is used to limit charge into a safe area. For that reason, UEM
has programmable charging cut-off limits VBATLim
1,2L,2H
(3.6 V / 5.0 V / 5.25 V). Maxi-
mum charging current is limited to 1.2 A. Default for VBATLim is 3.6 V (used for initial
charging of empty battery).
+
-
VBATTlim
Comp
Switch
Driver
Ctrl
Logic
Over
Temp.
Detection
VCHARin
VCHARout
VBATT
V
CHAR
VBATT
UEM
Current
Sensing/
Limit
Vmstr
WatchDog
PWM
Generator
PWM