LTC3558_15 Datasheet, PDF (11/32 Pages) Linear Technology – Linear USB Battery Charger with Buck and Buck-Boost Regulators

LTC3558
PIN FUNCTIONS
GND (Pin 1): Ground. Connect to Exposed Pad (Pin 21).
BAT (Pin 2): Charge Current Output. Provides charge cur-
rent to the battery and regulates final float voltage to 4.2V.
MODE (Pin 3): MODE Pin for Switching Regulators. When
held high, both regulators operate in Burst Mode Opera-
tion. When held low, the buck regulator operates in pulse
skip mode and the buck-boost regulator operates in PWM
mode. This pin is a high impedance input; do not float.
FB1 (Pin 4): Buck Regulator Feedback Voltage Pin. Re-
ceives feedback by a resistor divider connected across
the output.
EN1 (Pin 5): Enable Input Pin for the Buck Regulator. This
pin is a high impedance input; do not float. Active high.
SW1 (Pin 6): Buck Regulator Switching Node. External
inductor connects to this node.
PV_IN1 (Pin 7): Input Supply Pin for Buck Regulator. Con-
nect to BAT and PV_IN2. A single 10μF input decoupling
capacitor to GND is required.
PV_IN2 (Pin 8): Input Supply Pin for Buck-Boost Regulator.
Connect to BAT and PV_IN1. A single 10μF input decoupling
capacitor to GND is required.
SWAB2 (Pin 9): Switch Node for Buck-Boost Regulator
Connected to the Internal Power Switches A and B. External
inductor connects between this node and SWCD2.
SWCD2 (Pin 10): Switch Node for Buck-Boost Regulator
Connected to the Internal Power Switches C and D. External
inductor connects between this node and SWAB2.
V_OUT2 (Pin 11): Regulated Output Voltage for Buck-Boost
Regulator.
SUSP (Pin 12): Suspend Battery Charging Operation. A
voltage greater than 1.2V on this pin puts the battery char-
ger in suspend mode, disables the charger and resets the
termination timer. A weak pull-down current is internally
applied to this pin to ensure it is low at power-up when
the input is not being driven externally.
FB2 (Pin 13): Buck-Boost Regulator Feedback Voltage
Pin. Receives feedback by a resistor divider connected
across the output.
V_C2 (Pin 14): Output of the Error Amplifier and Voltage
Compensation Node for the Buck-Boost Regulator. Ex-
ternal Type I or Type III compensation (to FB2) connects
to this pin.
EN2 (Pin 15): Enable Input Pin for the Buck-Boost Regu-
lator. This pin is a high impedance input; do not float.
Active high.
HPWR (Pin 16): High Current Battery Charging Enabled.
A voltage greater than 1.2V at this pin programs the
BAT pin current at 100% of the maximum programmed
charge current. A voltage less than 0.4V sets the BAT pin
current to 20% of the maximum programmed charge
current. When used with a 1.74k PROG resistor, this pin
can toggle between low power and high power modes per
USB specification. A weak pull-down current is internally
applied to this pin to ensure it is low at power-up when
the input is not being driven externally.
NTC (Pin 17): Input to the NTC Thermistor Monitoring
Circuit. The NTC pin connects to a negative temperature
coefficient thermistor which is typically co-packaged with
the battery pack to determine if the battery is too hot or too
cold to charge. If the battery temperature is out of range,
charging is paused until the battery temperature re-enters
the valid range. A low drift bias resistor is required from
V_CC to NTC and a thermistor is required from NTC to
ground. To disable the NTC function, the NTC pin should
be tied to ground.
PROG (Pin 18): Charge Current Program and Charge
Current Monitor Pin. Charge current is programmed by
connecting a resistor from PROG to ground. When charg-
ing in constant-current mode, the PROG pin servos to 1V
if the HPWR pin is pulled high, or 200mV if the HPWR pin
is pulled low. The voltage on this pin always represents
the BAT pin current through the following formula:
I_BAT
=
PROG • 800
R_PROG
CHRG (Pin 19): Open-Drain Charge Status Output. The
CHRG pin indicates the status of the battery charger. Four
possible states are represented by CHRG charging, not
charging (i.e., the charge current is less than one-tenth
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