9
FN6430.0
February 14, 2007
Theory of Operation
The ISL9203A is an integrated charger for single-cell Li-ion
or Li-polymer batteries. The ISL9203A functions as a
traditional linear charger when powered with a voltage-
source adapter. When powered with a current-limited
adapter, the charger minimizes the thermal dissipation
commonly seen in traditional linear chargers.
As a linear charger, the ISL9203A charges a battery in the
popular constant current (CC) and constant voltage (CV)
profile. The constant charge current I
REF
is programmable
up to 1.5A with an external resistor. The charge voltage V
CH
has 1% accuracy over the entire recommended operating
condition range. The charger always preconditions the
battery with 10% of the programmed current at the beginning
of a charge cycle, until the battery voltage is verified to be
above the minimum fast charge voltage, V
MIN
. This low-
current preconditioning charge mode is named trickle mode.
The verification takes 15 cycles of an internal oscillator
whose period is programmable with the timing capacitor.
A thermal-foldback feature removes the thermal concern
typically seen in linear chargers. The charger reduces the
charge current automatically as the IC internal temperature
rises above +100°C to prevent further temperature rise. The
thermal-foldback feature guarantees safe operation when
the printed circuit board (PCB) is space limited for thermal
dissipation.
Two indication pins are available from the charger to indicate
the charge status. The V2P8 outputs a 2.8V DC voltage
when the input voltage is above the power-on reset (POR)
level and can be used as a power-present indication. This
pin is capable of sourcing a 2mA current, so it can also be
used to bias external circuits. The STATUS pin is an open-
drain logic output that goes LOW at the beginning of a
charge cycle and stays LOW until the end-of-charge (EOC)
condition is qualified. The EOC condition is met when the
battery voltage rises above a recharge threshold and the
charge current falls below an EOC current threshold. Once
the EOC condition is qualified, the STATUS output goes
HIGH and is latched. The latch is released at the beginning
of a re-charge cycle, when the EN is toggled, or after the
chip is power cycled.
If the ISL9203A has not been power cycled and has not had
the EN pin toggled, but the VSEN voltage drops below the
recharge level, then the device re-enters the charge mode.
In this condition, the charger indicates a re-charge cycle by
bringing the STATUS pin LOW.
When the wall adapter is not present, the ISL9203A draws
less than 1
µA of current from the battery.
Figure 18 shows the typical charge curves in a traditional
linear charger powered with a constant-voltage adapter.
From the top to bottom, the curves represent the constant
input voltage, the battery voltage, the charge current and the
power dissipation in the charger. The power dissipation P
CH
is given by the following equation:
(EQ. 1)
where I
CHARGE
is the charge current. The maximum power
dissipation occurs during the beginning of the CC mode. The
maximum power the IC is capable of dissipating is
dependent on the thermal impedance of the printed-circuit
board (PCB). Figure 18 shows, with dotted lines, two cases
that the charge currents are limited by the maximum power
dissipation capability due to the thermal foldback.
When using a current-limited adapter, the thermal situation in
the ISL9203A is totally different. Figure 19 shows the typical
charge curves when a current-limited adapter is employed.
The operation requires the I
REF
to be programmed higher
than the limited current I
LIM
of the adapter, as shown in
Figure 19. The key difference of the charger operating under
such conditions occurs during the CC mode.
P
CH
V
IN
V
BAT
–()I
CHARGE
⋅=
FIGURE 18. TYPICAL CHARGE CURVES USING A
CONSTANT-VOLTAGE ADAPTER
V
CH
V
MIN
V
IN
I
REF
I
REF
/10
P
1
P
2
P
3
TRICKLE
MODE
CONSTANT CURRENT
MODE
CONSTANT VOLTAGE
MODE
INHIBIT
INPUT VOLTAGE
BATTERY VOLTAGE
CHARGE CURRENT
POWER DISSIPATION
ISL9203A
