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LTC3554

3554f

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 VOUTevenifthereisinsufﬁcient

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.

OPERATION

Simpliﬁed PowerPath Block Diagram

100mA/500mA

INPUT CURRENT

LIMIT

CC/CV

CHARGER

15mV

IDEAL

3554 F01

VOUT

VBUS 20

BAT

LTC3554 Datasheet(PDF) 14 Page - Linear Technology

LTC3554 Datasheet(HTML) 14 Page - Linear Technology

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