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4. Circuit Description
Charger Sub-system
The MT6305 battery charger can be used with
Li-ion and NiMH batteries. BATUSE pin can set
MT6305 to fit the battery type.
When BATUSE is set low, Li-ion battery is
used. When BATUSE is set high, then NiMH
battery is used. MT6305 charges the battery in
three phases: pre-charging, constant current
mode charging, and constant voltage mode
charging. Figure 2 shows the flow chart of
charger behavior. The circuitry of MT6305
combines with a PMOS transistor, diode and
current-sense resistor externally to form a
simple and low cost linear charger shown in
Figure 3.
MT6305 is available pulsed top-off charging
algorithm by the CHRCNTL pin control from
baseband chipset.
Charge Detection
The MT6305 charger block has a detection
circuit that determinates if an adapter has been
applied to the CHRIN pin. If the adapter voltage
exceeds the battery voltage by 3.75%, the
CHRDET output will go high. If the adapter is
then removed and the voltage at the CHRIN pin
drops to only 2.5% above the VBAT pin,
CHRDET goes low.
Pre-Charging mode
When the battery voltage is below the UVLO
threshold, the charge current is in the pre-
charging mode. There are two steps in this
mode. While the battery voltage is deeply
discharged below 2V, a 10mA trickle current of
MT6305 charges the battery internally. When
the battery voltage exceeds 2V, the pre-charge
current is enabled, which allows 10mV
(typically) across the external current sense
resistor. This pre-charge current can be
calculated:
Copyright © 2007 LG Electronics. Inc. All right reserved.
LGE Internal Use Only
- 37 -
Only for training and service purposes
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