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MT6305B

GSM Power Management System

MediaTek Inc 

Confidential Information

MT6305B

Charge Detection

The MT6305 charger block has a detection circuit that

determinates if an adapter has been applied to the

CHRIN pin and senses the CHRIN voltage. The

maximum CHRIN voltage can be up to 15V but the

detection circuit will report invalid_CHRIN when

CHRIN>9V to protect the charging system. In other

words, the charger block will do charging when

CHRIN<=9V but stop charging when CHRIN>9V.

However, apply ing 9V<CHRIN<15V won’t damage

the IC. Based on valid_CHRIN, if the adapter voltage

exceeds the battery voltage by 3.0%, the CHRDET

output will go high. If the adapter is then removed and

the voltage at the CHRIN pin drops to only 3.0%

above the VBAT pin, CHRDET goes low.

Pre -Charging mode

When the battery voltage is below the UVLO thresh-

old, 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:

IPRE _ CHARGING

=

VSENSE

R1

= 10mV

R1

(2)

Constant Current Charging Mode

Once the battery voltage has exceeded the UVLO

threshold the charger will switch to the constant cur-

rent charging mode. The MT6305 allows 160mV

(typically) across the external current sense resistor.

This constant current can be calculated.

ICONSTANT

=

VSENSE

R1

=

160m V

R1

(3)

If the battery voltage is below 4. 2V of Li-ion battery

charging (5.1V of NiMH battery charging), the battery

will be in the constant current charging mode.

Constant Voltage Charging Mode

This mode is only applied to Li-ion battery charging. If

the battery has reached the final charge voltage, a

constant voltage is applied to the battery and keeps it

at 4.2V. The charge termination is determined by the

bas eband chip internally, which will pull the

CHRCNTL low to stop the charger.

Once the battery voltage exceeds 4.3V of Li-ion bat-

tery (5.1V of NiMH battery), a hardware over voltage

protection (OV) should be activated and turn off the

charger block of MT6305.

Pulsed Charging Algorithm

MT6305 is available to pulsed top-off charging algo-

rithm by the CHRCNTL pin. The control signal is from

bas eband chipset to limit the charging duty cycle.

This charging algorithm combines the efficiency of

switch-mode chargers with the simplicity and low cost

of linear chargers.

Battery Voltage Monitor

As the Table 2 shown, the relation of battery voltage

and charger control with the responsible signals are

listed. When Vbat <3.2V, an UVLO signal is active

low. When Vbat >= 4.3, an OV signal is active and

terminates charging. The disconnection of battery

could be detected by BATDET pin. BATDET is pulled

high internally when battery disconnected and termi-

nates charging immediately.

Table 2. Charger and Voltage Detection

Vbat

CHRON

CHRCNTL

CHRDET

-UVLO

Any Vbat

L

X

L

X

Vbat > 3.2V

X

L

X

H

Vbat < 3.2V

H

X

L

L

3.2V<Vbat<4.2V

H

H

H

H

Vbat = 4.2V

H

H

H

H

3.2V<Vbat

H

H

H

H

Notes: OV terminates charging at 4.3V for Li-ion battery or 5.1V for NiMH battery.

BATUSE

X

X

X

L

L

H

Charger

Condition

No- Charging

No- Charging

Pre- Charging

CC mode

CV mode

CC mode

MediaTek Confidential

Revision 1.1–Apr. 22, 2005

© 2002 MediaTek Inc.

The information contained in this document can be modified without notice

Page 28 of 33

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