User Guide

NHB–3
Technical Documentation
PAMS
HF Desktop Charger CHH–8P
Original 26/97 Page 16
Watchdog Circuits
Under normal operation the processor is pulsating the WTCHDOG–line to
reseting the ”power off”– and ”software reset”–watchdogs.
If the processor doesn’t run correctly, then the transistor V210 turns off and the
”Software reset”–watchdog V211 gives reset pulse through C211 to the RE-
SET–line. If after this reseting the processor still runs incorrectly, then the ”Pow-
er off”–watchdog (V212, V213) turns off the +5 V regulator N103.
Battery Charging
Charging current for the phone battery is fed in via transistor V311, which is
always on when the phone is connected to the system connector X701 on the
DC4 module. Phone battery charging state is indicated by the red (V344, V345)
and green (V333) leds. Because the phone and the spare battery cannot be
charged at the same time the charging current of the phone must be detected
and this is done with the current mirror V321 and corresponding resistors.
Charging current for the spare battery is fed in via switching transistor V221
and schotky diode V220. The transistor is controlled by the processor (SPARE
CHARGE –line). When the phone battery is not charged and it is allowed to
charge the spare battery, the transistor is on and a constant current is supplied
to the battery (the red led V331 lits). In the pulsed charging mode the charging
current is adjusted by pulsating this charge current (the green led V330 lits).
Spare battery voltage and ∆V–voltage are determined by reading the VBAT line
state. Voltages are measured through resistor divider R250 / R251 and the am-
plifier N250–B.
Spare battery size is determined by reading the BSI line state. This is pulled to
+5 V reference voltage by R243. 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
reference voltage by R242. In the battery pack an NTC resistor is connected
between BTEMP and GND.
Spare Battery Discharging
The desktop charger is also provided with a discharge function. This is
activated by pressing the discharge button S300. Resistors R230–R237
determines the discharge current which is fed through switching transistor V230
controlled by the processor. The discharging is indicated by blinking of the red
led V331. The battery is discharged to +5 V and thereafter charged normally to
full.