User Guide

NHB–3

Technical Documentation

PAMS

Desktop Charger CHH–2

Original 26/97 Page 8

AN5/CHVOL Charger voltage detection

AN7/LIREF Lithium reference voltage input

• range: 0...5 V

• resolution: 19.5 mV/bit

Charging the Spare Battery

Charging current for the spare battery is fed in via switching transistor V130

and Schottky diode V131. The transistor is controlled by the processor (BSW

line). When the transistor is on, a constant current is supplied to the battery.

This is the rapid charging mode. In the pulsed charging mode, charging current

is adjusted by pulsing this rapid charge current.

Battery voltage is measured through resistor divider R143/R144 (100/121

kohm). The range measured is 0 to 11 V; a voltage variation of 43 mV can be

detected. For improved resolution, i.e. rapid charge cut off, operational amplifier

N140 is added. This amplifies the battery voltage by a factor of (1 + 100

kohm/56 kΩ) and compares the result to a +5 V reference supply. The A/D con-

verter receives a battery voltage range of 7.0 to 11 V; a better resolution of 16

mV results.

Battery size is determined by reading the BSI line state. This is pulled to +5 V

reference voltage by R147 (100 kΩ). In the battery pack a ”size” resistor is con-

nected between BSI and GND.

Temperature is measured over the BTEMP line. This line is pulled to +5 V refer-

ence voltage by R145 (27 kΩ). In the battery pack an NTC resistor is connected

between BTEMP and GND.

Because the phone and the spare battery cannot be charged at the same time

the charging current of the phone must be detected. This is done at the A/D in-

put AN2 (PDET). The charging current for the phone is directed through series

diode V114. If the voltage drop across the diode is higher than 100 mV (corre-

sponds to A/D value of 5), charging current is flowing to the phone.

The CHH–2 desktop charger has two dual–colour LEDs to indicate the charging

states of the phone and the spare battery.

Discharging the Spare Battery

The desktop charger is also provided with a discharge function. This is acti-

vated by pressing a discharge switch on top of the charger. The spare battery is

then discharged before charging. Resistors R181–R188 determines the dis-

charge current which is fed through switching transistor V134 controlled by pro-

cessor over the DISW line (pin 64). The battery is discharged to 5 V and there-

after charged normally. The state of the discharge switch is read via the DBIN

line (pin 63).