ISL6297 Intersil Corporation, ISL6297 Datasheet - Page 7

• Manufacturer Part Number: ISL6297
• Description: Li-ion/Li Polymer Battery Charger
• Manufacturer: Intersil Corporation

Theory of Operation
The ISL6297 is based on the Intersil Patent-pending dual-
mode charging technology. This allows the ISL6297 to
function as a traditional linear charger when powered with a
voltage-source adapter. However, when powered with a
current-limited adapter, the charger minimizes the thermal
dissipation commonly seen in traditional linear chargers.
This dual-mode technology generates very low heat, which
enables the charger to be used in space-limited applications.
The ISL6297 charges a Lithium Ion battery using the
constant current (CC) and constant voltage (CV) profile
specified by battery cell manufacturers.
As a linear charger, the constant charge current I
programmable up to 1.5A with an external resistor. The
constant charge voltage V
4.2V with a 0.7% accuracy over the entire recommended
operating range.
The ISL6297 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
charge mode is named trickle mode.
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.
FIGURE 1. TYPICAL CHARGE CURVES USING A
I
REF
V
V
I
V
REF
/10
MIN
P
P
P
CH
IN
1
2
3
Trickle
Mode
Input Voltage
CONSTANT-VOLTAGE ADAPTER
Constant Current
MIN
Mode
. This low-current preconditioning
CH
is regulated by the ISL6297 at
TIMEOUT
7
Constant Voltage
Power Dissipation
Mode
Battery Voltage
Charge Current
REF
Inhibit
is
ISL6297
Figure 1 shows the typical charge curves in a traditional
linear charger powered with a constant-voltage adapter. The
power dissipation P
where I
dissipation occurs at 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 1 shows, with dotted lines, two cases in
which the charge currents are limited by the maximum power
dissipation capability due to the thermal foldback.
To take advantage of the low-heat feature of the ISL6297, a
current-limited AC/DC converter is required as the power
supply to the charger. The current-limited supply has the I-V
characteristics shown in Figure 2. The supply is a DC source
before the load current reaches the limited current I
Once the current limit is reached, the supply current cannot
increase further; instead, the supply voltage falls. The
current-limited supply is a voltage source with an equivalent
output impedance or a current source, depending on its
operating region, as shown in Figure 2.
In this mode of operation, the constant current is determined
by the current limit I
current charge mode. To ensure dual-mode operation, the
current protection level set by the ISL6297 I
be higher than I
the battery voltage is regulated at 4.2V. When the battery
voltage is below the specified V
preconditions the battery using trickle charge mode.
Figure 3 shows the typical waveforms in a charge cycle of the
dual mode operation. When the battery voltage is below V
the trickle charge mode is in effect. Since the charge current is
much less than the I
voltage source region. Once the battery voltage exceeds
V
MOSFET. The AC/DC converter operates in the current-
limitedregion and its voltage is pulled down to a level slightly
higher than the battery voltage.
MIN
FIGURE 2. THE I-V CHARACTERISTICS OF THE CURRENT-
, the charger fully turns on the internal P-channel power
P
V
V
CH
CHARGE
NL
FL
=
(
LIMITED AC/DC CONVERTER
V
IN
LIM
is the charge current. The maximum power
-V
V
. In the constant-voltage charge mode,
C
r
CH
BAT
LIM
LIM
NL
O
is given by the following equations:
, the AC/DC converter operates in the
) I
of the supply during the constant-
×
CHARGE
MIN
r
O
voltage, the charger
= (V
I
LIM
NL
- V
REF
FL
)/I
I
LIM
LIM
pin should
March 20, 2007
B
A
LIM
FN9215.1
(EQ. 1)
.
MIN
,