ISL6292 Datasheet, PDF (9/19 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger

ISL6292
Theory of Operation
The ISL6292 is an integrated charger for single-cell Li-ion or
Li-polymer batteries. The ISL6292 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 ISL6292 charges a battery in the
popular constant current (CC) and constant voltage (CV)
profile. The constant charge current I_REF is programmable
up to 2A (1.5A for the 3x3 DFN package) with an external
resistor or a logic input. 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.
A TEMP pin monitors the battery temperature to ensure a
safe charging temperature range. The temperature range is
programmable with an external negative temperature
coefficient (NTC) thermistor. The TEMP pin is also used to
detect the removal of the battery.
The charger offers a safety timer for setting the fast charge
time (TIMEOUT) limit to prevent charging a dead battery for
an extensively long time. The TIMEOUT limit can be
Trickle
Mode
Constant Current Constant Voltage
Mode
Mode
Inhibit
V_IN
Input Voltage
V_CH
Battery Voltage
V_MIN
I_REF
I_REF/10
P₁
P₂
P₃
Charge Current
Power Dissipation
TIMEOUT
FIGURE 17. TYPICAL CHARGE CURVES USING A
CONSTANT-VOLTAGE ADAPTER
disabled as needed by the TOEN pin. The trickle mode is
limited to 1/8 of TIMEOUT and cannot be disabled by the
TOEN pin.
The charger automatically re-charges the battery when the
battery voltage drops below a recharge threshold. When the
wall adapter is not present, the ISL6292 draws less than 1µA
current from the battery.
Three 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 the 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 turns LOW at the beginning
of a charge cycle until the end-of-charge (EOC) condition is
qualified. The EOC condition is: the battery voltage rises
above the recharge threshold and the charge current falls
below a user-programmable EOC current threshold. Once
the EOC condition is qualified, the STATUS output rises to
HIGH and is latched. The latch is released at the beginning
of a charge or re-charge cycle. The open-drain FAULT pin
turns low when any fault conditions occur. The fault
conditions include the external battery temperature fault, a
charge time fault, or the battery removal.
Figure 17 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 equations:
P_CH = (V_IN-V_BAT) ⋅ I_CHARGE
(EQ. 1)
where I_CHARGE is the charge current. The maximum power
dissipation occurs during the beginning of the CC mode. The
Trickle
Mode
V_IN
V_CH
Constant Current
Mode
Input Voltage
Constant Voltage
Mode
Inhibit
Battery Voltage
V_MIN
I_REF
I_LIM
I_REF/10
Charge Current
P₁
Power Dissipation
P₂
TIMEOUT
FIGURE 18. TYPICAL CHARGE CURVES USING A CURRENT-
LIMITED ADAPTER
9
FN9105.6
July 25, 2005