LTC3577_15 Datasheet, PDF (20/54 Pages) Linear Technology – Highly Integrated 6-Channel Portable PMIC

LTC3577/LTC3577-1
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 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 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
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 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
FROM AC ADAPTER (OR HIGH VOLTAGE BUCK OUTPUT)
4.3V
(RISING)
–
3.2V
(FALLING)
+
WALL
4
+
–
42
V_C
OPTIONAL CONTROL
FOR HIGH VOLTAGE BUCK REGS
LT3480, LT3481 OR LT3505
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
3577 F01
+
Li-Ion
3577fa