ISL6292_07 Datasheet, PDF (10/20 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 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.
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
10
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 2.8VDC
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 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 Equation 1:
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
maximum power the IC is capable of dissipating is
dependent on the thermal impedance of the printed-circuit
board (PCB). Figure 17 shows (with dotted lines) two cases
that the charge currents are limited by the maximum power
dissipation capability due to the thermal foldback.
Trickle
Mode
Constant Current Constant Voltage Inhibit
Mode
Mode
V_IN
Input Voltage
V_CH
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
FN9105.9
December 17, 2007