Datasheet

LTC3677-3
19
36773f
operaTion
PowerPath OPERATION
Introduction
The LTC3677-3 is 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
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
LTC3677-3 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 LTC3677-3 through an external device such as a power
Schottky or FET, as shown in Figure 1. The LTC3677-3 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 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 LTC3677-3 also includes 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 2.25MHz
constant-frequency current mode step-down switching
regulators provide 500mA, 500mA and 800mA each and
+
–
+
–
+
–
+
–
4.3V
(RISING)
3.2V
(FALLING)
75mV (RISING)
25mV (FALLING)
ENABLE
USB CURRENT LIMIT
CONSTANT-CURRENT
CONSTANT-VOLTAGE
BATTERY CHARGER
WALL
FROM AC ADAPTER
4
V
BUS
FROM
USB
40
37
+
–
15mV
IDGATE
BAT
36773 F01
Li-Ion
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
BAT
IDEAL
DIODE
38
39
V
OUT
V
OUT
41
ACPR
+
SYSTEM
LOAD
Figure 1. Simplified PowerPath Block Diagram