LTC3550 Datasheet, PDF (10/24 Pages) Linear Technology – Dual Input USB/AC Adapter Li-Ion Battery Charger with 600mA Buck Converter

LTC3550
PI FU CTIO S
USBIN (Pin 1): USB Input Supply Pin. Provides power to
the battery charger. The maximum supply current is 650mA.
This should be bypassed with a 1µF capacitor.
IUSB (Pin 2): USB Charge Current Program and Monitor
Pin. The charge current can be set by connecting a resis-
tor, R_IUSB, to ground. When charging in constant-current
mode, this pin servos to 1V. The voltage on this pin can
be used to measure the charge current delivered from the
USB input using the following formula:
I_BAT
=
V_IUSB
R_IUSB
• 1000
ITERM (Pin 3): Termination Current Threshold Program
Pin. The current termination threshold, I_TERMINATE, can be
set by connecting a resistor, R_ITERM, to ground. I_TERMINATE
is set by the following formula:
I_TERMINATE
=
100V
R_ITERM
When the charge current, I_BAT, falls below the termination
threshold, charging stops and the ^⎯C^⎯H^⎯R^⎯G output becomes
high impedance.
This pin is internally clamped to approximately 1.5V. Driv-
ing this pin to voltages beyond the clamp voltage should
be avoided.
⎯P⎯W⎯R (Pin 4): Open-Drain Power Supply Status Output.
When the DCIN or USBIN pin voltage is sufficient to
begin charging (i.e., when the supply is greater than
the undervoltage lockout threshold and at least 180mV
above the battery terminal), the ^⎯P^⎯W^⎯R pin is pulled low by
an internal N-channel MOSFET. Otherwise, ^⎯P^⎯W^⎯R is high
impedance. The output is capable of sinking up to 10mA,
making it suitable for driving an LED.
⎯C⎯H⎯R⎯G (Pin 5): Open-Drain Charge Status Output. When
the LTC3550 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. This output
is capable of sinking up to 10mA, making it suitable for
driving an LED.
V_FB (Pin 6): Voltage Feedback Pin. Receives the feedback
voltage from an external resistor divider across the buck
regulator output.
V_CC (Pin 7): Buck Regulator Input Supply Pin. Must be
closely decoupled to GND (Pins 8, 9) with a 2.2µF or
greater ceramic capacitor.
GND (Pins 8, 9): Ground.
SW (Pin 10): Buck Regulator Switch Node Connection to
Inductor. This pin connects to the drains of the internal
main (top) and synchronous (bottom) power MOSFET
switches.
RUN (Pin 11): Buck Regulator Run Control Input. Forcing
this pin above 1.5V enables the regulator. Forcing this pin
below 0.3V shuts it down. In shutdown, all buck regulator
functions are disabled drawing <1µA supply current from
V_CC. Do not leave RUN floating.
EN (Pin 12): Charger Enable Input. A logic low on this pin
enables the charger. If this input is left floating, an internal
2MΩ pull-down resistor defaults the LTC3550 to charge
mode. Pull this pin high to disable the charger.
HPWR (Pin 13): USB High/Low Power Mode Select Input.
Used to control the amount of current drawn from the
USB port. A logic high on the HPWR pin sets the charge
current to 100% of the current programmed by the IUSB
pin. A logic low on the HPWR pin sets the charge current
to 20% of the current programmed by the IUSB pin. An
internal 2MΩ pull-down resistor defaults the charger to
its low current state.
IDC (Pin 14): Wall Adapter Charge Current Program and
Monitor Pin. The charge current is set by connecting a
resistor, R_IDC, to ground. When charging in constant-
current mode, this pin servos to 1V. The voltage on this
pin can be used to measure the charge current using the
following formula:
I_BAT
=
V_IDC
R_IDC
•
1000
BAT (Pin 15): Charger Output. This pin provides charge
current to the battery and regulates the final float voltage
to 4.2V.
3550fa
10