Charging The Spare Battery; Discharging The Spare Battery; Watchdog Circuit - Nokia 2160 Technical Documentation Manual

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Technical Documentation
AN5/CHVOL
AN7/LIREF

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 proces-
sor (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 sup-
ply. The A/D converter 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" re-
sistor is connected between BSI and GND.
Temperature is measured over the BTEMP line. This line is pulled to +5 V
reference 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 input 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 (corresponds 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
activated by pressing a discharge switch on top of the charger. The spare
battery is then discharged before charging. Resistors R181–R188 deter-
mines the discharge current which is fed through switching transistor
V134 controlled by processor over the DISW line (pin 64). The battery is
discharged to 5 V and thereafter charged normally. The state of the dis-
charge switch is read via the DBIN line (pin 63).

Watchdog Circuit

The processor generates positive pulses to output PC7 (pin 18). These
pulses are received by transistor V201 discharging capacitor C161. The
Original 50/96
Charger voltage detection
Lithium reference voltage input
range: 0...5 V
resolution: 19.5 mV/bit
Desktop Charger CHH–2
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