LTC3456 Datasheet, PDF (9/28 Pages) Linear Technology – 2-Cell, Multi-Output DC/DC Converter with USB Power Manager

LTC3456
PI FU CTIO S
AIN (Pin 1): Low-Battery Detector Input Pin. The detector
compares the voltage on this pin to an 800mV reference.
Connect the resistor divider tap to this pin to set the low-
battery trip point.
AO (Pin 2): Open-Drain Digital Output. This open-drain
logic output is pulled to GND whenever the AIN pin voltage
falls lower than 0.8V.
AGND (Pin 3): Analog Ground. All resistor dividers should
be connected to this pin.
V_BATT (Pin 4): Battery Input Supply. The input voltage at this
pin can range from 1.8V to 3.2V. Must be locally bypassed
with a 1µF (or greater) X5R or X7R type ceramic capacitor.
SW1 (Pin 5): Switch Pin for Core Regulator. Connect the
inductor between SW1 and the output capacitor. Keep
these PCB trace lengths as short and wide as possible to
reduce EMI.
PGND (Pin 6): Power Ground. This is the ground pin for all
internal drivers and switches. Provide a short PCB path
between PGND and PCB system ground.
WALLFB (Pin 7): Wall Feedback Pin. This pin receives the
feedback voltage from an external resistor divider across
the AC wall adapter input. When the pin voltage is higher
than 1.25V, the chip is powered from the V_EXT pin and the
USB switch is turned off. Ensure that the resistor ratio is
set so that the wall adapter voltage (min) is still high
enough to make V_EXT > 4V. Connect to ground if not used.
EXT_PWR (Pin 8): External Power Good Pin. This open-
drain logic output is pulled to GND whenever the WALLFB
pin is pulled higher than 1.25V or the USB pin voltage is
greater than 4V and SUSPEND is low. Essentially this pin
is pulled low whenever the AC adapter or the USB power
is present. When pulled low, this pin is capable of sinking
5mA suitable for driving an external LED.
V_EXT (Pin 9): External Power Pin. This pin is connected to
the USB pin via an internal 0.5Ω (typ) PMOS switch. The
AC wall adapter can be connected to this pin through a
Schottky diode. An onboard voltage detector prevents the
IC from drawing power from this pin until the pin voltage
rises above 4V. The voltage detector for V_EXT has built-in
150mV hysteresis. Connect a 10µF X5R or X7R type
ceramic capacitor from this pin to ground.
USB (Pin 10): USB Input Supply. Input current into this pin
is limited to either 100mA or 500mA based on the state of
the USBHP pin. When the USB pin voltage is greater than
4V and SUSPEND is low, and WALLFB is less than 1.25V,
USB is connected to the V_EXT pin via an internal 0.5Ω
current limited PMOS Switch. Connect a 4.7µF (X5R or
X7R type) ceramic capacitor in series with a 1Ω resistor
from this pin to ground.
V_MAX (Pin 11): Maximum Supply Voltage Pin. A special
internal PowerPath^TM controller monitors the V_BATT, V_INT,
V_EXT and USB voltages and passes the highest available
supply voltage to the V_MAX pin. This pin is used to power
some of the internal circuitry of the IC. Connect a 1µF
bypass capacitor from this pin to ground. It can be used
to supply a maximum of 1mA output load. The V_MAX
output voltage stays alive even when the IC is in shutdown.
USBHP (Pin 12): USB High Power Select Pin. This pin is
used to set the USB current limit. Pull high to select 500mA
current limit (High Power mode); low to select 100mA
current limit (Low Power mode). This pin has a weak pull-
down current source to ensure that Low Power mode is in
effect during start-up.
SW2_BK (Pin 13): Switch Pin for Main Regulator (USB or
Wall Powered). Connect the inductor between SW2_BK
and the output voltage. Keep these PCB trace lengths as
short and wide as possible to reduce EMI.
SW2_BST (Pin 14): Switch Pin for Main Regulator (Bat-
tery Powered). Connect the inductor between SW2_BST
and V_BATT. Keep these PCB trace lengths as short and wide
as possible to reduce EMI.
V_INT (Pin 15): Internal Supply Voltage Pin. The V_INT
voltage is regulated to 3.3V. This pin is used to power most
of the internal circuitry of the IC. Do not load this output.
Connect an output capacitor from this pin to ground.
V_MAIN (Pin 16): Main Regulator Output Voltage. An inter-
nal 0.4Ω PMOS switch connects this pin to the V_INT pin
0.8ms (typ) after the Core voltage comes into regulation.
This ensures that V_MAIN will always power up after Core
output during start-up. Connect an output capacitor from
this pin to ground.
PowerPath is a trademark of Linear Technology Corporation.
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