FAN54300 Datasheet, PDF (23/43 Pages) Fairchild Semiconductor – USB-Compliant, Dual-Power Input, Single-Cell, Li-Ion Switching Charger with USB-OTG Boost Regulator

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.
The FAN54300 combines two highly integrated synchronous
buck regulators for charging from two separate power
sources. The IC also includes 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.
In addition to its USB (VBUS) input, the FAN54300 allows a
second power source (VIN) to be used for charging. This input
source is typically a "wall wart" and can be up to 9.5 V input.
The FAN54300 has three operating modes:
 Charge Mode:
Charges a single-cell Li-Ion or Li-polymer battery.
 Boost Mode:
Provides 5 V 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 PWRIN (the charging power source) to
the battery, or from the battery to PWRIN, are blocked in
this mode. This mode consumes very little current from
PWRIN or the battery.
When the IC is charging the battery from VIN, the boost
regulator may be simultaneously enabled to supply 5 V for
OTG peripherals.
Charge Mode
In Charge Mode, FAN54300 employs five regulation loops:
1. VBUS 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 RSENSE resistor.
3. Charge voltage: The regulator is restricted from
exceeding this voltage. As the internal battery voltage
rises, the battery’s internal impedance and RSENSE works
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
RSENSE drops below the ITERM threshold.
4. Temperature: If the IC’s junction temperature reaches
120°C, charge current is continuously reduced until the
IC’s temperature stabilizes at 120°C.
5. An additional loop limits the amount of drop on VBUS or
VIN to a programmable voltage (VSP) to accommodate
current-limited wall chargers.
Input Source Selection
The FAN54300 selects the power source (PWRIN) for
charging according to the following criteria.
Table 3. PWRIN: Charging Power Input Source Selection
V_IN
VALID
INVALID
VALID
V_BUS
INVALID
VALID
VALID
PWRIN
VIN
VBUS
VIN
If charging is in progress with VBUS and VIN becomes valid,
charging from VBUS stops and charging continues from VIN.
Charging stops if HZ_VIN is set when VIN becomes valid while
charging with VBUS.
If VIN and VBUS are both connected and t15MIN expires, both
CE# bits are set. To reinitiate t15MIN charging (autocharge) with
a weak battery, both power sources must be unplugged, then
a valid power source plugged in. If only one of the two
connected sources are removed then connected with a weak
battery, both CE# bits remain set.
Fault Reporting and Register Reset
All faults that occur during charging or boost are reported only
in the STATUS register (R0) associated with the active
charging source at the time of the fault. Any register reset that
occurs due to t32SEC overflow resets only the registers
associated with the active charging source.
For example: Assume the IC is charging in 32-Second Mode
with VIN as a source. The processor stops setting TMR_RST,
so t32SEC expires. The IC then resets only the _V registers and
goes into 15-Minute Mode charging with VIN. A timer fault is
enunciated, but reported in the CONTROL0_V register.
CONTROL0_U is unaffected by this event. When the t15MIN
timer expires, the IC sets the CE#_V bit, but leaves the
CE#_U bit unchanged.
Battery Charging Curve
If the battery voltage is below VSHORT, a linear current source
“pre-charges” the battery until VBAT reaches VSHORT. The PWM
charging circuits are 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 FAN54300 is designed to work with a current-limited input
source at PWRIN. During the current regulation phase of
charging, PWRIN current limitations or the programmed
charging current limit the amount of current available to
charge the battery and power the system. The effect of input
power limitations on ICHARGE can be seen in Figure 47.
© 2010 Fairchild Semiconductor Corporation
FAN54300 • Rev. 1.0.4
23
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