FAN54013_12 Datasheet, PDF (17/36 Pages) Fairchild Semiconductor – FAN54010 / FAN54011 / FAN54012 / FAN54013 / FAN54014

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.
FAN5401X combines a highly integrated synchronous buck
regulator for charging with a synchronous boost regulator,
which can supply 5 V 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 FAN5401X has three operating modes:
1. Charge Mode:
Charges a single-cell Li-ion or Li-polymer battery.
2. Boost Mode:
Provides 5 V power to USB-OTG with an integrated
synchronous rectification boost regulator using the
battery as input.
3. 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.
Note: Default settings are denoted by bold typeface.
Charge Mode
In Charge Mode, FAN5401X employs four regulation loops:
1. Input Current: Limits the amount of current drawn from
VBUS. This current is sensed internally and can be
programmed through the I²C interface.
2. Charging Current: Limits the maximum charging current.
This current is sensed using an external R_SENSE resistor.
3. Charge Voltage: The regulator is restricted from
exceeding this voltage. As the internal battery voltage
rises, the battery’s internal impedance and R_SENSE work
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_SENSE drops below the I_TERM threshold.
4. Temperature: If the IC’s junction temperature reaches
120°C, charge current is reduced until the IC’s
temperature stabilizes at 120°C.
5. An additional loop limits the amount of drop on VBUS to
a programmable voltage (V_SP) to accommodate “special
chargers” that limit current to a lower current than might
be available from a “normal” USB wall charger.
Battery Charging Curve
If the battery voltage is below V_SHORT, a linear current source
pre-charges the battery until V_BAT reaches V_SHORT. The PWM
charging circuit is then started and the battery is charged
with a constant current if sufficient input power is available.
The current slew rate is limited to prevent overshoot.
The FAN5401X is designed to work with a current-limited
input source at VBUS. During the current regulation phase of
charging, I_INLIM or the programmed charging current limits the
amount of current available to charge the battery and power
the system. The effect of I_INLIM on I_CHARGE can be seen in
Figure 36.
V_OREG
I_OCHARGE
I_CHARGE
V ^BAT
V_SHORT
I_SHORT
I_TERM
PRE- CURRENT REGULATION
VOLTAGE
CHARGE
REGULATION
Figure 35. Charge Curve, I_CHARGE Not Limited by I_INLIM
V_OREG
V_SHORT
I_SHORT
V ^BAT
I_CHARGE
I_TERM
PRE- CURRENT REGULATION
VOLTAGE
CHARGE
REGULATION
Figure 36. Charge Curve, I_INLIM Limits I_CHARGE
Assuming that V_OREG is programmed to the cell’s fully
charged “float” voltage, the current that the battery accepts
with the PWM regulator limiting its output (sensed at VBAT)
to V_OREG declines, and the charger enters the voltage
regulation phase of charging. When the current declines to
the programmed I_TERM value, the charge cycle is complete.
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 3.5 V to 4.44 V in 20 mV increments, as
shown in Table 3.
© 2011 Fairchild Semiconductor Corporation
FAN5401X Family • Rev. 1.0.4
17
www.fairchildsemi.com