Desk Top Charger - Samsung SGH-600 Service Manual

Circuit Description

2-10 Desk Top Charger

2-10-1 Charging
The desk-top charger contains switching regulator to charge a lithium battery from an DC/DC adaptor. The
battery type is detected at pin 15 (MPU) through U5 ( front port) and U26 (rear port). Battery charging current
is turned into Vi. Vi is measured at pin 12 (MPU) after R32 and C23 to cancel the noise. When the battery
voltage is too low, the charging circuit turns to trickle mode using Q9 and Q11.
2-10-2 Control Part
This circuit contains 4-bit micro controller (U21), including an I/O port, timer, A/D converter to control battery
charging. This circuit uses a 4 MHz main clock and +5V power.
BATTERY VOLTAGE DETECTION
Battery voltage from the front port is detected at R20, R18 and measured at pin 13 (MPU).
Battery voltage from the rear port is detected at R14, R13 and measured at pin 14 (MPU).
BATTERY TEMPERATURE DETECTION
The charger always detects the battery temperature via NTC thermistor to prevent battery thermal problems.
This circuit is composed of parallel resistors because NTC thermistor has log-scale thermal characteristics. If the
battery temperature exceeds 55 degrees C, charging stops.
AUTONOMOUS TIMER
If MPU has stopped charging and the timer goes to the ÔonÕ state by an external shock, overcharging may occur.
A timer (U7-4) prevents the battery from being overcharged by any unexpected external influence.
2-8 Samsung Electronics