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12 of 14

SS8000G

APPLICATION INFORMATION (cont.)

Charge Detection

The SS8000 charger block has a detection circuit that

determines via the CHRIN pin if an adapter has been

connected. 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 from

the SS8000 charges the battery. When the battery

voltage exceeds 2V, the pre-charge current is enabled,

which allows 10mV (typically) across the external cur-

rent sense resistor. This pre-charge current can be cal-

culated:

1

R

mV

10

1

R

V

I

SENSE

CHARGING

_

PRE

=

=

(2)

Constant Current Charging Mode

Once the battery voltage has exceeded the UVLO

threshold, the charger will switch to the constant current

charging mode. The SS8000 allows 160mV (typically)

across the external current sense resistor. This constant

current can be calculated.

1

R

mV

160

1

R

V

I

SENSE

CONSTANT

=

=

(3)

If the battery voltage is below 4.2V when charging a

Li-ion battery (5.1V for a NiMH battery), the constant

current charging mode is used.

Constant Voltage Charging Mode

This mode only applies 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.

This termination of charging is determined by the base-

band chip internally, which will pull the CHRCNTL low to

stop the charger.

Once the battery voltage exceeds 4.3V for a Li-ion bat-

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

protection (OV) should be activated to turn off the

charger block of the SS8000.

Pulsed Charging Algorithm

The SS8000 provide a pulsed top-off charging algo-

rithm via the CHRCNTL pin. The control signal from the

baseband chipset limits 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 Table 2 shows, the relationship between battery

voltage and charger control with the corresponding sig-

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

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

charging is halted.

Table 2. Charger and Voltage Detection

Vbat

Charger_on

Chr_cntl

Chr_Det

Output

-UV

Batuse

Charger

Condition

Any Vbat

L

X

L

X

X

No-Charging

Vbat > 3.2V

X

L

X

X

X

No-Charging

Vbat < UV

H

X

H

L

X

Pre-Charging

3.2V<Vbat<4.2V

H

H

H

H

L

CC mode

Vbat = 4.2V

H

H

H

H

L

CV mode

3.2V<Vbat

H

H

H

H

H

CC mode

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

12/06/2004 Rev.2.10