ISL6256 INTERSIL [Intersil Corporation], ISL6256 Datasheet - Page 13

• Manufacturer Part Number: ISL6256
• Description: Highly Integrated Battery Charger with Automatic Power Source Selector for Notebook Computers
• Manufacturer: INTERSIL [Intersil Corporation]

PGND
PGND is the power ground. Connect PGND to the source of
the low side MOSFET.
VDD
VDD is an internal LDO output to supply IC analog circuit.
Connect a 1µF ceramic capacitor to ground.
VDDP
VDDP is the supply voltage for the low-side MOSFET gate
driver. Connect a 4.7Ω resistor to VDD and a 1µF ceramic
capacitor to power ground.
ICOMP
ICOMP is a current loop error amplifier output.
VCOMP
VCOMP is a voltage loop amplifier output.
CELLS
This pin is used to select the battery voltage. CELLS = VDD
for a 4S battery pack, CELLS = GND for a 3S battery pack,
CELLS = Float for a 2S battery pack.
VADJ
VADJ adjusts battery regulation voltage. VADJ = VREF for
4.2V + 5%/cell; VADJ = Floating for 4.2V/cell; VADJ = GND
for 4.2V - 5%/cell. Connect to a resistor divider to program
the desired battery cell voltage between 4.2V - 5% and
4.2V + 5%.
CHLIM
CHLIM is the battery charge current limit set pin. CHLIM
input voltage range is 0.1V to 3.6V. When CHLIM = 3.3V, the
set point for CSOP-CSON is 165mV. The charger shuts
down if CHLIM is forced below 88mV.
ACLIM
ACLIM is the adapter current limit set pin. ACLIM = VREF for
100mV, ACLIM = Floating for 75mV, and ACLIM = GND for
50mV. Connect a resistor divider to program the adapter
current limit threshold between 50mV and 100mV.
VREF
VREF is a 2.39V reference output pin. It is internally
compensated. Do not connect a decoupling capacitor.
Theory of Operation
Introduction
Note: Unless otherwise noted, all descriptions that refer to
the ISL6256 also refer to the ISL6256A.
The ISL6256 includes all of the functions necessary to
charge 2 to 4 cell Li-ion and Li-polymer batteries. A high
efficiency synchronous buck converter is used to control the
charging voltage and charging current up to 10A. The
ISL6256 has input current limiting and analog inputs for
setting the charge current and charge voltage; CHLIM inputs
13
ISL6256, ISL6256A
are used to control charge current and VADJ inputs are used
to control charge voltage.
The ISL6256 charges the battery with constant charge
current, set by CHLIM input, until the battery voltage rises up
to a programmed charge voltage set by VADJ input; then the
charger begins to operate at a constant voltage charge mode.
The charger also drives an adapter isolation P-Channel
MOSFET to efficiently switch in the adapter supply.
ISL6256 is a complete power source selection controller for
single battery systems and also aircraft power applications.
It drives a battery selector P-Channel MOSFET to efficiently
select between a single battery and the adapter. It controls
the battery discharging MOSFET and switches to the battery
when the AC adapter is removed, or, switches to the AC
adapter when the AC adapter is inserted for single battery
system.
The EN input allows shutdown of the charger through a
command from a micro-controller. It also uses EN to safely
shutdown the charger when the battery is in extremely hot
conditions. The amount of adapter current is reported on the
ICM output. Figure 1 shows the IC functional block diagram.
The synchronous buck converter uses external N-Channel
MOSFETs to convert the input voltage to the required
charging current and charging voltage. Figure 2 shows the
ISL6256 typical application circuit with charging current and
charging voltage fixed at specific values. The typical
application circuit shown in Figure 3 shows the ISL6256
typical application circuit which uses a micro-controller to
adjust the charging current set by CHLIM input for aircraft
power applications. The voltage at CHLIM and the value of
R
generates the control signals to drive two external
N-Channel MOSFETs to regulate the voltage and current set
by the ACLIM, CHLIM, VADJ and CELLS inputs.
The ISL6256 features a voltage regulation loop (VCOMP)
and two current regulation loops (ICOMP). The VCOMP
voltage regulation loop monitors CSON to ensure that its
voltage never exceeds the voltage and regulates the battery
charge voltage set by VADJ. The ICOMP current regulation
loops regulate the battery charging current delivered to the
battery to ensure that it never exceeds the charging current
limit set by CHLIM; and the ICOMP current regulation loops
also regulate the input current drawn from the AC adapter to
ensure that it never exceeds the input current limit set by
ACLIM, and to prevent a system crash and AC adapter
overload.
PWM Control
The ISL6256 employs a fixed frequency PWM current mode
control architecture with a feed-forward function. The
feed-forward function maintains a constant modulator gain of
11 to achieve fast line regulation as the buck input voltage
changes. When the battery charge voltage approaches the
input voltage, the DC/DC converter operates in dropout
1
sets the charging current. The DC/DC converter
September 14, 2010
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