Datasheet

LTC3577/LTC3577-1
20
3577fa
OPERATION
PowerPath OPERATION
Introduction
The LTC3577 is a highly integrated power management
IC that features:
– PowerPath controller
– Battery charger
– Ideal diode
– Input overvoltage protection
– Pushbutton controller
– Three step-down switching regulators
– High voltage buck regulator V
C
controller
– Two low dropout linear regulators
– 40V LED backlight controller
Designed specifi cally for USB applications, the PowerPath
controller incorporates a precision input current limit
which communicates with the battery charger to ensure
that input current does not violate the USB average input
current specifi cation. The ideal diode from BAT to V
OUT
guarantees that ample power is always available to V
OUT
even if there is insuffi cient or absent power at V
BUS
. The
LTC3577 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
OUT
pin of the
LTC3577 through an external device such as a power
Schottky or FET as shown in Figure 1. The LTC3577 has
the unique ability to use the output, which is powered by
an external supply, to charge the battery while provid-
ing 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
OUT
to V
BUS
when a wall adapter is pres-
ent. The LTC3577 provides a V
C
output pin which can be
used to drive the V
C
pin of an external high voltage buck
switching regulator such as the LT3480, LT3653 or LT3505
to provide power to the V
OUT
pin. The V
C
control circuitry
adjusts the regulation point of the switching regulator to
+
–
+
–
+
–
+
–
4.3V
(RISING)
3.2V
(FALLING)
75mV (RISING)
25mV (FALLING)
ENABLE
USB CURRENT LIMIT
CONSTANT CURRENT
CONSTANT VOLTAGE
BATTERY CHARGER
WALL
FROM AC ADAPTER (OR HIGH VOLTAGE BUCK OUTPUT)
4
V
BUS
FROM
USB
40
37
+
–
15mV
IDGATE
BAT
3577 F01
Li-Ion
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
BAT
IDEAL
DIODE
38
39
V
OUT
V
OUT
V
C
OPTIONAL CONTROL
FOR HIGH VOLTAGE BUCK REGS
LT3480, LT3481 OR LT3505
41
ACPR
42
+
SYSTEM
LOAD
Figure 1. Simplifi ed PowerPath Block Diagram