LTC3559-1_15 Datasheet, PDF (9/24 Pages) Linear Technology – Linear USB Battery Charger with Dual Buck Regulators

LTC3559/LTC3559-1
PIN FUNCTIONS
GND (Pin 1): Ground, Connect to Exposed Pad (Pin 17).
BAT (Pin 2): Charge Current Output. Provides charge cur-
rent to the battery and regulates final float voltage to 4.2V
(LTC3559) or 4.1V (LTC3559-1).
MODE (Pin 3): MODE Pin for Buck Regulators. When held
high, both regulators are in Burst Mode operation. When
held low both regulators operate in pulse skip mode. This
pin is a high impedance input; do not float.
FB1 (Pin 4): Buck 1 Feedback Voltage Pin. Receives feed-
back by a resistor divider connected across the output.
EN1 (Pin 5): Enable Input Pin for Buck 1. This pin is a high
impedance input; do not float. Active high.
SW1 (Pin 6): Buck 1 Switching Node. External inductor
connects to this node.
PV_IN (Pin 7): Input Supply Pin for Buck Regulators.
Connect to BAT. A 2.2μF decoupling capacitor to GND is
recommended.
SW2 (Pin 8): Buck 2 Switching Node. External inductor
connects to this node.
EN2 (Pin 9): Enable Input Pin for Buck 2. This pin is a high
impedance input; do not float. Active high.
FB2 (Pin 10): Buck 2 Feedback Voltage Pin. Receives feed-
back by a resistor divider connected across the output.
SUSP (Pin 11): Suspend Battery Charging Operation.
A voltage greater than 1.2V on this pin puts the battery
charger into 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.
HPWR (Pin 12): 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 13): 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 re-
quired from V_CC to NTC and a thermistor is required from
NTC to ground. To disable the NTC function, the NTC pin
should be grounded.
PROG (Pin 14): 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 battery current through the following formula:
I_BAT
=
PROG
R_PROG
• 800
CHRG (Pin 15): 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 1/10th of the
full-scale charge current), unresponsive battery (i.e., the
battery voltage remains below 2.9V after 1/2 hour of charg-
ing) and battery temperature out of range. CHRG requires
a pull-up resistor and/or LED to provide indication.
V_CC (Pin 16): Battery Charger Input. A 1μF decoupling
capacitor to GND is recommended.
Exposed Pad (Pin 17): Ground. The Exposed Pad must
be soldered to PCB ground to provide electrical contact
and rated thermal performance.
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