LTC4088EDE-2 查看數據表（PDF） - Linear Technology

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LTC4088EDE-2

High Efficiency Battery Charger/USB Power Manager with Regulated Output Voltage

Linear Technology 

LTC4088-1/LTC4088-2

Operation

Introduction

The LTC4088-1/LTC4088-2 includes a PowerPath control-

ler, battery charger, internal ideal diode, external ideal diode

controller and a SUSPEND LDO. Designed specifically for

USB applications, the PowerPath controller incorporates a

precision average input current limited step-down switch-

ing regulator to make maximum use of the allowable USB

power. Because power is conserved, the LTC4088-1/

LTC4088-2 allows the load current on VOUT to exceed the

current drawn by the USB port without exceeding the USB

load specifications.

The switching regulator and battery charger communicate

to ensure that the average input current never exceeds the

USB specifications.

The ideal diodes from BAT to VOUT guarantee that ample

power is always available to VOUT even if there is insuf-

ficient or absent power at VBUS.

Finally, to prevent battery drain when a device is con-

nected to a suspended USB port, an LDO from VBUS to

VOUT provides either low power or high power suspend

current to the application.

Input Current Limited Step Down Switching Regulator

The power delivered from VBUS to VOUT is controlled

by a 2.25MHz constant frequency step-down switching

regulator. To meet the USB maximum load specification,

the switching regulator contains a measurement and

control system that ensures that the average input cur-

rent remains below the level programmed at CLPROG.

VOUT drives the combination of the external load and the

battery charger.

If the combined load does not cause the switching power

supply to reach the programmed input current limit, VOUT

will track approximately 0.3V above the battery voltage.

By keeping the voltage across the battery charger at this

low level, power lost to the battery charger is minimized.

Figure 1 shows the power path components.

If the combined external load plus battery charge current

is large enough to cause the switching power supply to

reach the programmed input current limit, the battery

charger will reduce its charge current by precisely the

amount necessary to enable the external load to be satis-

fied. Even if the battery charge current is programmed to

exceed the allowable USB current, the USB specification

for average input current will not be violated; the battery

charger will reduce its current as needed. Furthermore, if

the load current at VOUT exceeds the programmed power

from VBUS, load current will be drawn from the battery via

the ideal diodes even when the battery charger is enabled.

The current at CLPROG is a precise fraction of the VBUS

current. When a programming resistor and an averaging

TO USB

OR WALL

ADAPTER

10

VBUS

11

ISWITCH/N

PWM AND

GATE DRIVE

SW

12

VOUTS 3

VOUT

10

CONSTANT CURRENT

CONSTANT VOLTAGE

BATTERY CHARGER

IDEAL

DIODE

+

OV

–

15mV +–

GATE

8

2 CLPROG

–

+

1.188V

AVERAGE INPUT

CURRENT LIMIT

CONTROLLER

0.3V

+–

3.6V

AVERAGE OUTPUT

VOLTAGE LIMIT

CONTROLLER

Figure 1

BAT

9

408812 F01

SYSTEM LOAD

3.5V TO

(BAT + 0.3V)

EXTERNAL

IDEAL DIODE

PMOS

+ SINGLE CELL

Li-Ion

40881fc

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