English
Language : 

LTC3554 Datasheet, PDF (14/36 Pages) Linear Technology – Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators
◁
LTC3554
OPERATION
Introduction
The LTC3554 is a highly integrated power management
IC that includes the following features:
PowerPath controller
Battery charger
Ideal diode
Pushbutton controller
Two step-down switching 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 never violates the USB specifications.
The ideal diode from BAT to VOUT guarantees that ample
power is always available to VOUT even if there is insufficient
or absent power at VBUS. The LTC3554 also includes a
pushbutton input to control the two synchronous step-
down switching regulators and system reset. The two
constant-frequency current mode step-down switching
regulators provide 200mA each and support 100% duty
cycle operation as well as operating in Burst Mode operation
for high efficiency at light load. No external compensation
components are required for the switching regulators.
Either regulator can be programmed for a minimum out-
put voltage of 0.8V and can be used to power a micro-
controller core, microcontroller I/O, memory or other
logic circuitry. The buck regulators can be operated at
1.125MHz or 2.25MHz. They also include a low power
standby mode which can be used to power essential
keep-alive circuitry while draining ultralow current from
the battery for extended battery life.
USB PowerPath Controller
The input current limit and charger control circuits of the
LTC3554 are designed to limit input current as well as
control battery charge current as a function of IVOUT. VOUT
drives the combination of the external load, the two step-
down switching regulators and the battery charger.
If the combined load does not exceed the programmed
input current limit, VOUT will be connected to VBUS through
an internal 350mΩ P-channel MOSFET. If the combined
load at VOUT exceeds the programmed input current limit,
the battery charger will reduce its charge current by the
amount necessary to enable the external load to be satisfied
while maintaining the programmed input current. Even if
the battery charge current is set to exceed the allowable
USB current, the average input current USB specification
will not be violated. Furthermore, load current at VOUT will
always be prioritized and only excess available current will
be used to charge the battery.
The input current limit is programmed by the HPWR and
SUSP pins. If SUSP pin set high, the input current limit
is disabled. If SUSP pin is low, the input current limit is
enabled. HPWR pin selects between 100mA input current
limit when it is low and 500mA input current limit when
it is high.
Simplified PowerPath Block Diagram
VBUS 20
100mA/500mA
INPUT CURRENT
LIMIT
CC/CV
CHARGER
18 VOUT
IDEAL
15mV
17 BAT
3554 F01
3554p
14
 ▷