FAN5404 Fairchild Semiconductor, FAN5404 Datasheet - Page 17

• Manufacturer Part Number: FAN5404
• Description: The FAN5404 combines a highly integrated switched-mode charger, to minimize single-cell Lithium-ion (Li-ion) charging time from a USB power source, and a boost regulator to power a USB peripheral from the battery
• Manufacturer: Fairchild Semiconductor

Circuit Description / Overview
When charging batteries with a current-limited input source,
such as USB, a switching charger’s high efficiency over a
wide range of output voltages minimizes charging time.
FAN540X combines a highly integrated synchronous buck
regulator for charging with a synchronous boost regulator,
which can supply 5V to USB On-The-Go (OTG) peripherals.
The regulator employs synchronous rectification for both the
charger and boost regulators to maintain high efficiency over
a wide range of battery voltages and charge states.
The FAN540X has three operating modes:
1.
2.
3.
Note: Default settings are denoted by bold typeface.
Charge Mode
In Charge Mode, FAN540X employs four regulation loops:
1.
2.
3.
4.
In addition, the FAN5403-05 employ an additional loop to
limit the amount of drop on VBUS to a programmable voltage
(V
a lower current than might be available from a “normal” USB
wall charger.
Battery Charging Curve
If the battery voltage is below V
pre-charges the battery until V
charging circuit is then started and the battery is charged
© 2009 Fairchild Semiconductor Corporation
FAN5400 Family • Rev. 1.0.7
SP
) to accommodate “special chargers” that limit current to
Charge Mode:
Charges a single-cell Li-ion or Li-polymer battery.
Boost Mode:
Provides 5V power to USB-OTG with an integrated
synchronous rectification boost regulator using the
battery as input.
High-Impedance Mode:
Both the boost and charging circuits are OFF in this
mode. Current flow from VBUS to the battery or from the
battery to VBUS is blocked in this mode. This mode
consumes very little current from VBUS or the battery.
Input Current: Limits the amount of current drawn from
VBUS. This current is sensed internally and can be
programmed through the I
Charging Current: Limits the maximum charging current.
This current is sensed using an external R
Charge Voltage: The regulator is restricted from
exceeding this voltage. As the internal battery voltage
rises, the battery’s internal impedance and R
in conjunction with the charge voltage regulation to
decrease the amount of current flowing to the battery.
Battery charging is completed when the voltage across
R
Temperature: If the IC’s junction temperature reaches
120°C, charge current is continuously reduced until the
IC’s temperature stabilizes at 120°C.
SENSE
drops below the I
TERM
BAT
2
C interface.
SHORT
threshold.
reaches V
, a linear current source
SHORT
SENSE
. The PWM
SENSE
resistor.
work
17
with a constant current if sufficient input power is available.
The current slew rate is limited to prevent overshoot.
The FAN540X is designed to work with a current-limited
input source at VBUS. During the current regulation phase of
charging, I
amount of current available to charge the battery and power
the system. The effect of I
Figure 36.
Assuming that V
charged “float” voltage, the current that the battery accepts
with the PWM regulator limiting its output (sensed at VBAT)
to V
regulation phase of charging. When the current declines to
the programmed I
Charge current termination can be disabled by resetting the
TE bit (REG1[3]).
The charger output or “float” voltage can be programmed by
the OREG bits from 3.5V to 4.44V in 20mV increments, as
shown in Table 3.
V
I
V
I
V
V
I
OCHARGE
SHORT
Figure 35. Charge Curve, I
SHORT
OREG
SHORT
OREG
SHORT
OREG
Figure 36. Charge Curve, I
INLIM
declines, and the charger enters the voltage
CHARGE
CHARGE
PRE-
PRE-
or the programmed charging current limits the
OREG
TERM
I
CHARGE
CURRENT REGULATION
CURRENT REGULATION
value, the charge cycle is complete.
is programmed to the cell’s fully
INLIM
CHARGE
on I
INLIM
CHARGE
Not Limited by I
I
I
TERM
TERM
Limits I
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REGULATION
REGULATION
VOLTAGE
VOLTAGE
can be seen in
CHARGE
INLIM