User Guide

NHM-8NX
System Module & UI PAMS Technical Documentation
Page 22 ãNokia Corporation Issue 1 05/02
Charge Control
In active mode charging is controlled by UEM’s digital part. Charging voltage and current
monitoring is used to limit charge into safe area. For that reason UEM has programmable
charging cut-off limits VBATLim
1,2L,2H
(3.6V / 5.0V / 5.25V). Maximum charging current
is limited to 1.2 A. Default for VBATLim is 3.6V (used for Initial charging of empty bat-
tery).
VBATLim
1,2L,2H
are designed with hysteresis. When the voltage rises above
VBATLim
1,2L,2H
+ charging is stopped by turning charging switch OFF. No change in oper-
ational mode is done. After voltage has decreased below VBATLim
-
charging re-starts.
If VBAT is detected to rise above the programmed limit, the output signal OVV is set to ‘1’
by CHACON. If charging current limit is reached OVC output is set ‘1’ by CHACON.
Pulse-width-Modulated (PWM) control signals PWM1 and PWM32 are generated by
UEM’s digital part to CHACON block.
In principle there are two PWM frequencies in use depending on the type of the charger
(standard charger 1Hz, fast charger 32Hz. Duty cycle range is 0% to 100%), but in NHM-
8NX only the 1Hz mode will be used, as all charger will be treated as standard charges
(2-wire types).
Supported Chargers
Supported chargers are:
• 2-wire chargers: ACP-7, ACP-8 and ACP-12.
• 3-wire chargers: PPH-1, ACP-9,, ACT-1, LCH-8 and LCH-9.
The 3-wire chargers have a 3 wire interface to the phone, 2 power and 1 control. The
control wire carries the 32Hz digital pulse width modulated signal which must be gener-
ated by the phone to control the charger output voltage. In NHM-8NX the 32Hz PWM
for the charger is connected to GND inside the bottom connector. This sets full charger
output voltage and equals 0% PWM from charger point of view.
Charger Interface Protection
In order to ensure safe operation with all chargers and in misuse/fail situations charger
interface is protected using transient voltage suppressor (TVS) and 1.5A fuse. TVS used in
NHM-8NX is 16V@175W device.