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LTC3577-3 Datasheet, PDF (20/52 Pages) Linear Technology – Highly Integrated Portable Product PMIC | |||
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LTC3577-3/LTC3577-4
OPERATION
PowerPath OPERATION
Introduction
The LTC3577-3/LTC3577-4 are highly integrated power
management IC that includes the following features:
â PowerPath controller
â Battery charger
â Ideal diode
â Input overvoltage protection
â Pushbutton controller
â Three step-down switching regulators
â Two low dropout linear regulators
â 40V LED backlight controller
Designed speciï¬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 speciï¬cation. The ideal diode from BAT to VOUT
guarantees that ample power is always available to VOUT
even if there is insufï¬cient or absent power at VBUS. 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 VOUT 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 conï¬gured to
detect the presence of the wall adapter and shut off the
connection to the USB. This prevents reverse conduction
from VOUT to VBUS 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)
â
3.2V
(FALLING)
+
WALL
4
+
â
FROM
USB
VBUS
40
+â
75mV (RISING)
25mV (FALLING)
ENABLE
USB CURRENT LIMIT
VOUT
ACPR
41
VOUT
39
CONSTANT-CURRENT
CONSTANT-VOLTAGE
BATTERY CHARGER
IDEAL
DIODE
+
â
+â 15mV
IDGATE
37
SYSTEM
LOAD
OPTIONAL
EXTERNAL
IDEAL DIODE
PMOS
20
BAT
Figure 1. Simpliï¬ed PowerPath Block Diagram
BAT
38
357734 F01
+
Li-Ion
357734fa
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