LTC3577-4_15 Datasheet, PDF (20/52 Pages) Linear Technology – Highly Integrated Portable Product PMIC

LTC3577-3/LTC3577-4
OPERATION
PowerPath OPERATION
Introduction
The LTC3577-3/LTC3577-4 are highly integrated power
management IC that includes the following features:
– PowerPath controller
– Battery charger
– Ideal diode
– Input overvoltage protection
– Pushbutton controller
– Three step-down switching regulators
– Two low dropout linear regulators
– 40V LED backlight controller
Designed specifically 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 specification. The ideal diode from BAT to V_OUT
guarantees that ample power is always available to V_OUT
even if there is insufficient or absent power at V_BUS. The
LTC3577-3/LTC3577-4 also have 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 LTC3577-3/LTC3577-4 through an
external device such as a power Schottky or FET as shown
in Figure 1. The LTC3577-3/LTC3577-4 have 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 configured 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 present.
The LTC3577-3/LTC3577-4 also include a pushbutton
input to control the power sequencing of two synchronous
step-down switching regulators (Buck1 and Buck2), a low
dropout regulator (LDO2) and system reset. The three
FROM AC ADAPTER
4.3V
(RISING)
–
3.2V
(FALLING)
+
WALL
4
+
–
FROM
USB
V_BUS
40
+–
75mV (RISING)
25mV (FALLING)
ENABLE
USB CURRENT LIMIT
V_OUT
ACPR
41
V_OUT
39
CONSTANT-CURRENT
CONSTANT-VOLTAGE
BATTERY CHARGER
IDEAL
DIODE
+
–
+– _15mV
IDGATE
37
SYSTEM
LOAD
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
20
BAT
Figure 1. Simplified PowerPath Block Diagram
BAT
38
357734 F01
+
Li-Ion
357734fb