NJW4100
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Ver.2006-08-03
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FEATURE DESCRIPTION
1. Voltage Detection Block (VS pin)
The VS pin determines charge voltage, low voltage, over voltage, and re-charge voltage. Battery voltage conditions are
constantly monitored. (Figure 1)
1-1. Charge Voltage (VS pin)
Charge voltage V
BAT
is set using the VS pin external
resistors R
B1
and R
B2
and the following equation:
V
BAT
=
2B
2B1B
R
RR +
x V
REF-CV (4.2V)
Using the following settings makes it easy to support
applications for one or two cells: for one cell, R
B1
= short,
and R
B2
= open; for two cells, R
B1
=R
B2
.
If you use a high resistance, the VS pin's bias current will
cause incorrect values. Use as low a resistance as
possible.
1-2. Overcharge Detection Block (VS pin)
The overcharge detection block stops charging when a
high voltage is detected at the VS pin.
The overcharge detection voltage is obtained with the following equation:
V
OV
=V
BAT
× 1.025 (typ.)
When overcharge is detected, charging is prohibited and LED-R blinks. After that, charge will continue to be prohibited, even
after battery voltage drops to a normal value. Turning the power off to release UVLO, battery connection detection, or
CHG-SW switching will enable the charge sequence to restart.
1-3. Low Voltage Detection (2mA charge) Block (VS pin, CS1 pin)
The low voltage detection block detects an
over-discharged battery, or an open battery caused by
the battery protection circuit or the like. This will
determine a 2mA charge prior to pre-charging.
The low voltage detection voltage is obtained with the
following equation:
V
LV
=V
BAT
× 0.475 (typ.)
During a 2mA charge, the block monitors battery voltage
recovery while a steady 2mA current is output from the
CS1 pin. (Figure 2)
If voltage does not recover within a prescribed time, the
timer will prohibit 2mA charging. Turning the power off to
release UVLO, battery connection detection, or CHG-SW
switching will enable the charge sequence to restart.
1-4. Re-Charge Detection (VS pin)
When a fully charged battery is left for a long period of time, voltage will drop due to self-discharge. The re-charge detection
block detects a drop in voltage and re-charges the battery.
The re-charge detection voltage is obtained with the following equation.
V
R-CHG
=V
BAT
× 0.95 (typ.)
Low Voltage
Detection
12dB
CS1
R
B1
R
B2
VS
Rcs
CS2
To Ch arg e
Output
Control Bloc
2mA Charge
Current
To Charge Current
Control Amp
2mA Charge
V
BAT
x 0.475
R
B1
R
B2
VS
To C h a r g e
Control Bloc
To O R
Circuit
Charge Voltage
Control Amp
V
REF2
CVCC-ON
Low Voltage
Detection
Over Voltage
Detection
Recharge
Detection
Quick Charge
Detection
Battery
Voltage
Detection
For 1 Cell
R
B1
: Short
R
B2
: Open
V
BAT
x 0.95
V
BAT
x 0.73
V
BAT
x 1.025
V
BAT
x 0.475
Figure 1. Voltage Detection Block Configuration
Figure 2. 2mA Charging Block