LTC3550 Linear Technology, LTC3550 Datasheet - Page 10

• Manufacturer Part Number: LTC3550
• Description: Dual Input USB/AC Adapter Li-Ion Battery Charger
• Manufacturer: Linear Technology

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PI FU CTIO S
LTC3550
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
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:
ITERM (Pin 3): Termination Current Threshold Program
Pin. The current termination threshold, I
set by connecting a resistor, R
is set by the following formula:
When the charge current, I
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 suffi cient 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.
10
U
I
I
BAT
TERMINATE
IUSB
=
, to ground. When charging in constant-current
R
U
V
IUSB
IUSB
=
• 1000
R
100
ITERM
U
V
BAT
ITERM
, falls below the termination
, to ground. I
TERMINATE
TERMINATE
, can be
V
voltage from an external resistor divider across the buck
regulator output.
V
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
EN (Pin 12): Charger Enable Input. A logic low on this pin
enables the charger. If this input is left fl oating, 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
current mode, this pin servos to 1V. The voltage on this
pin can be used to measure the charge current using the
following formula:
BAT (Pin 15): Charger Output. This pin provides charge
current to the battery and regulates the fi nal fl oat voltage
to 4.2V.
FB
CC
CC
I
BAT
. Do not leave RUN fl oating.
(Pin 6): Voltage Feedback Pin. Receives the feedback
(Pin 7): Buck Regulator Input Supply Pin. Must be
=
R
V
IDC
IDC
IDC
, to ground. When charging in constant-
• 1000
3550fa