LTC3552 Datasheet, PDF (8/24 Pages) Linear Technology – Standalone Linear Li-Ion Battery Charger and Dual Synchronous Buck Converter

LTC3552
PI FU CTIO S
ITERM (Pin 1): Charge Termination Program. The charge
termination current threshold is programmed by connect-
ing a 1% resistor, R_TERM, to ground. The current threshold
ITERM, is set by the following formula:
100V
100V
I_TERM = _RTERM , R_TERM = _ITERM
BAT (Pin 2): Charge Current Output. Provides charge cur-
rent to the battery from the internal P-channel MOSFET,
and regulates the final float voltage to 4.2V. An internal
precision resistor divider from this pin sets the float volt-
age. This divider is disconnected in shutdown mode to
minimize current drain from the battery.
⎯C⎯H⎯R⎯G (Pin 3): Charge Status Open-Drain Output. When
the battery is charging, the ^⎯C^⎯H^⎯R^⎯G pin is pulled low by an
internal N-channel MOSFET. When the charge cycle is
completed, ^⎯C^⎯H^⎯R^⎯G becomes high impedance.
MODE/SYNC (Pin 4): Combination Mode Selection and
Oscillator Synchronization. This pin controls the operation
of the buck regulators. When tied to V_CC or GND, Burst
Mode operation or pulse-skipping mode is selected, re-
spectively. Do not float this pin. The oscillation frequency
can be synchronized to an external oscillator applied to this
pin and pulse-skipping mode is automatically selected.
SW2 (Pin 5): Regulator 2 Switch Node Connection to the
Inductor. This pin swings from V_CC to GND.
P⎯ O⎯ R⎯ (Pin 6): Power-On Reset. This open-drain logic output
is pulled to GND when either output voltage drops 8.5%
from the regulated voltage and goes high after 262,144
clock cycles when both regulators are within regulation.
RUN2 (Pin 7): Regulator 2 Enable. Forcing this pin to
V_CC enables regulator 2, while forcing it to GND causes
regulator 2 to shut down. This pin must be driven; do
not float.
V_FB2 (Pin 8): Output Feedback for Regulator 2. Receives
the feedback voltage from the external resistive divider
across the output. Normal voltage for this pin is 600mV.
V_FB1 (Pin 9): Output Feedback for Regulator 1. Receives
the feedback voltage from the external resistive divider
across the output. Normal voltage for this pin is 600mV.
RUN1 (Pin 10): Regulator 1 Enable. Forcing this pin to
V_CC enables regulator 1, while forcing it to GND causes
regulator 1 to shut down. This pin must be driven; do
not float.
V_CC (Pin 11): Buck Regulators Input Supply. Provides
power to the switchers. Must be closely decoupled
to GND.
SW1 (Pin 12): Regulator 1 Switch Node Connection to the
Inductor. This pin swings from V_CC to GND.
PROG (Pin 13): Charge Current Program and Charge
Current Monitor. Charge current is programmed by con-
necting a 1% resistor, R_PROG, to ground. When charging
in constant-current mode, this pin servos to 1V. In all
modes, the voltage on this pin can be used to measure
the charge current using the following formula:
I_BAT
=
V_PROG
I_PROG
• 1000
This pin is clamped to approximately 2.4V. Driving this pin to
voltages beyond the clamp voltage should be avoided.
V_IN (Pin 14): Charger Input Supply. Provides power to
the charger. V_IN can range from 4.25V to 8V. This pin
should be bypassed with at least a 1µF capacitor. When
V_IN is within 100mV of the BAT pin voltage, the charger
enters shutdown mode dropping the battery drain current
to less than 2µA.
⎯_P⎯_W⎯_{R (Pin 15): Charger Power Supply Status Open-Drain}
Output. When V_IN is greater than the undervoltage lock-
out threshold and at least 100mV above V_BAT, the
⎯_P⎯_W⎯_{R pin is pulled to ground; otherwise, the pin is high}
impedance.
⎯E⎯N (Pin 16): Enable Input. A logic high on the ⎯E⎯N pin will
put the charger into shutdown mode where the battery
drain current is reduced to less than 2µA and the supply
current is reduced to less than 50µA. A logic low or floating
the ^⎯E^⎯N pin (allowing an internal 2MΩ pull-down resistor
to pull this pin low) enables charging.
Exposed Pad (GND) (Pin 17): Ground. The exposed
backside of the package (Pin 17) is ground and must be
soldered to the PCB for maximum heat transfer.
3552f
8