LTC3455_15 Datasheet, PDF (8/28 Pages) Linear Technology – Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger

LTC3455/LTC3455-1
PIN FUNCTIONS
FB2 (Pin 18): Feedback Pin for Switcher 2. Set the output
voltage by connecting feedback resistors to this pin.
ON2 (Pin 19): Enable Pin for Switcher 2. This pin turns on
Switcher 2 only if ON is low or PWRON is high. Switcher
2 cannot be turned on by itself.
RST (Pin 20): Reset Pin. This pin is an open-drain output
that provides a 200ms reset signal during power-up to
initialize a microcontroller.
MODE (Pin 21): Burst Mode Enable Pin. Tie this pin high
to allow Burst Mode operation for the LTC3455/LTC3455-1.
Burst Mode operation will provide superior efficiency when
both outputs are operating with very low output currents.
Tie this pin to ground to force PWM operation under all
load current conditions. Burst Mode is disabled initially
at startup (for 200ms) and also whenever external power
is available (even if MODE is pulled high).
PWRON (Pin 22): Power-On Pin. Pull this pin high to turn
on the LTC3455/LTC3455-1. This pin is typically used in
conjunction with the ON and PBSTAT pins, and a momen-
tary-on switch. Tie PWRON to ground if not used.
PBSTAT (Pin 23): Push-Button Status Pin. This pin is an
open drain output that indicates the state of the ON pin
(which is usually connected to a momentary-on push-but-
ton) to the microcontroller. This pin follows the state of the
ON pin (PBSTAT goes low when ON is pulled low).
ON (Pin 24): ON Pin. Pull this pin to ground to turn on
the LTC3455/LTC3455-1. This pin is typically used with
a momentary-on push-button switch to turn on the
LTC3455/LTC3455-1. This pin would be held low until the
PWRON pin is pulled high by a microcontroller to keep the
LTC3455/LTC3455-1 turned on. If a momentary-on switch
is not used, this pin can be held to ground to keep on the
LTC3455/LTC3455-1. Leave ON open if not used. This pin
has a weak pull-up current source.
GND (Pin 25 – Exposed Pad): Ground Pin. The exposed
backside pad is the only ground pin for the LTC3455/
LTC3455-1 and must be soldered to the PC board ground
plane for the device to operate properly.
SIMPLIFIED BLOCK DIAGRAM
USB POWER
3.9V TO 5.3V
Li-Ion BATTERY
3.3V TO 4.2V
USE FOR LDO
OR LOW BATTERY
INDICATOR
USB POWER
MANAGER
V_MAX IS CONNECTED TO THE BEST
AVAILABLE INPUT POWER SOURCE
(WALL ADAPTER, USB OR BATTERY)
BATTERY
PMOS SWITCH
SWITCHER 1
BATTERY
CHARGER
SWITCHER 2
GAIN BLOCK
HOT SWAP
3455 SBD
5V WALL ADAPTER
V_MAX
USE TO POWER OTHER
DC/DCs AND LDOs
V_OUT1
1.8V TYPICAL
V_OUT2
3.3V TYPICAL
HOT SWAP OUTPUT
3.3V TYPICAL
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