ISL6292D Datasheet, PDF (7/13 Pages) Intersil Corporation – Li-ion/Li Polymer Battery Charger

ISL6292D
Theory of Operation
The ISL6292D is an integrated charger for single-cell Li-ion
or Li-polymer batteries. The ISL6292D 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 ISL6292D 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 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 Inhibit
Mode
Mode
V_IN
Input Voltage
V_CH
Battery Voltage
V_MIN
I_REF
I_REF/10
P₁
P₂
P₃
Charge Current
Power Dissipation
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 ISL6292D draws less than
3µA 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 STAT1 pin is
an open-drain logic output that turns LOW when the battery
is being charged and turns HIGH when the 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 STAT1 output rises to
HIGH and is latched. The latch is released at the beginning
of a charge or re-charge cycle. The STAT1 pin blinks when a
fault occurs. The blinking frequency of a TIMEOUT fault is
twice as fast as a temperature fault. The STAT2 pin behaves
the same as the STAT1 except that it blinks at one frequency
only when any fault occurs.
Figure 2 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)
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
FIGURE 2. TYPICAL CHARGE CURVES USING A
CONSTANT-VOLTAGE ADAPTER
7
FIGURE 3. TYPICAL CHARGE CURVES USING A CURRENT-
LIMITED ADAPTER