LTC3557 LINER [Linear Technology], LTC3557 Datasheet - Page 12

• Manufacturer Part Number: LTC3557
• Description: USB Power Manager with Li-Ion Charger and Three Step-Down Regulators
• Manufacturer: LINER [Linear Technology]

LTC3557/LTC3557-1
Introduction
The LTC3557/LTC3557-1 is a highly integrated power
management IC that includes a PowerPath controller,
battery charger, an ideal diode, an always-on LDO, three
synchronous step-down switching regulators as well as
a buck regulator V
USB applications, the PowerPath controller incorporates
a precision input current limit which communicates with
the battery charger to ensure that input current never
violates the USB specifi cations.
The ideal diode from BAT to V
power is always available to V
or absent power at V
The LTC3557/LTC3557-1 also has the ability to receive
power from a wall adapter or other non-current-limited
power source. Such a power supply can be connected
to the V
external device such as a power Schottky or FET as shown
in Figure 1.
OPERATION
12
FROM
OUT
USB
pin of the LTC3557/LTC3557-1 through an
FROM AC ADAPTER (OR HIGH VOLTAGE BUCK OUTPUT)
24
3
WALL
V
BUS
C
(FALLING)
(RISING)
controller. Designed specifi cally for
BUS
4.3V
3.2V
.
+
–
OUT
75mV (RISING)
25mV (FALLING)
OUT
–
+
+
–
even if there is insuffi cient
guarantees that ample
Figure 1. Simplifi ed PowerPath Block Diagram
USB CURRENT LIMIT
FOR HIGH VOLTAGE BUCK REGS
LT3480, LT3481 OR LT3505
ENABLE
OPTIONAL CONTROL
26
V
C
CONSTANT CURRENT
CONSTANT VOLTAGE
BATTERY CHARGER
The LTC3557/LTC3557-1 has the unique ability to use
the output, which is powered by an external supply, to
charge the battery while providing power to the load. A
comparator on the WALL pin is confi gured to detect the
presence of the wall adapter and shut off the connection
to the USB. This prevents reverse conduction from V
to V
The LTC3557/LTC3557-1 provides a V
can be used to drive the V
buck switching regulator such as the LT3480, LT3481, or
LT3505 to provide power to the V
circuitry adjusts the regulation point of the switching
regulator to a small voltage above the BAT pin voltage.
This control method provides a high input voltage, high
effi ciency battery charger and PowerPath function.
An “always on” LDO provides a regulated 3.3V from V
This LDO will be on at all times and can be used to supply
up to 25mA.
BUS
V
BAT
when a wall adapter is present.
OUT
IDEAL
DIODE
–
+
15mV
+
–
ACPR
GATE
V
C
OUT
BAT
35571 F01
pin of an external high voltage
25
23
21
22
OUT
+
pin. The V
C
Li-Ion
output pin which
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
SYSTEM
LOAD
C
control
35571fc
OUT
OUT
.