Nokia 3105 Servicehandbuch

CCS Technical Documentation

Troubleshooting — BB

RH-48

Issue 1 11/2003

© 2003 Nokia Corporation         Confidential 

Page 21

Connecting a charger creates voltage on VCHAR input of the UEM. When VCHAR input 
voltage level is detected to rise above 2 V (VCHdet+ 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 three steps:

1 Check that the charger output (voltage and current) is within safety limits.

2 Identify the charger as a two-wire or three-wire charger.

3 Check that the charger is within the charger window (voltage and current).

If the charger is accepted and identified, the appropriate charging algorithm is initiated.

In active mode, charging is controlled by UEM’s digital part. Charging voltage and cur-
rent monitoring is used to limit charging into safe area. For that reason UEM has pro-
grammable charging cut-off limits:

VBATLim1=3.6 V (Default)

VBATLim2L=5.0 V and

VBATLim2H=5.25 V.

VBATLim1, 2L, 2H are designed with hystereses. When the voltage rises above VBATLim1, 
2L, 2H+ charging is stopped by turning charging switch OFF. No change in operational 
mode is done. After voltage has decreased below VBATLim- charging re-starts. 

There are two PWM frequencies in use depending on the type of the charger: two-wire 
charger uses a 1Hz and a three-wire charger uses a 32Hz. Duty cycle range is 0% to 
100%. Maximum charging current is limited to 1.2 A.

________

F100

0

2

1.5A

L100

2

X102

1

42R/100MHz

"VCHARIN"

CHARGER(4:0)

V100

C106

1n0