LTC3548EDD-2(RevA) Просмотр технического описания (PDF) - Linear Technology

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LTC3548EDD-2
(Rev.:RevA)

Dual Synchronous, Fixed/Adjustable Output, 2.25MHz Step-Down DC/DC Regulator

Linear Technology 

LTC3548-2

Dual Synchronous,

Fixed/Adjustable Output, 2.25MHz

Step-Down DC/DC Regulator

FEATURES

■ High Efficiency: Up to 95%

■ 1.8V/800mA Fixed Output and 400mA Adjustable

Output Voltage

■ Only 40µA Quiescent Current (Both Channels)

■ 2.25MHz Constant Frequency Operation

■ High Switch Current Limits: 1.2A and 0.7A

■ No Schottky Diodes Required

■ Low RDS(ON) Internal Switches: 0.35Ω

■ Current Mode Operation for Excellent Line

and Load Transient Response

■ Short-Circuit Protected

■ Low Dropout Operation: 100% Duty Cycle

■ Ultralow Shutdown Current: IQ < 1µA

■ Power-On Reset Output

■ Externally Synchronizable Oscillator

■

Small

Thermally

Enhanced

U

3mm

×

3mm

DFN

Package

APPLICATIO S

■ PDAs/Palmtop PCs

■ Digital Cameras

■ Cellular Phones

■ Portable Media Players

■ PC Cards

■ Wireless and DSL Modems

DESCRIPTIO

The LTC®3548-2 is a dual, constant frequency, synchro-

nous step down DC/DC converter. Intended for low power

applications, it operates from 2.5V to 5.5V input voltage

range and has a constant 2.25MHz switching frequency,

allowing the use of tiny, low cost capacitors and inductors

with a profile ≤1.2mm. For channel 1, the output voltage

is fixed at 1.8V/800mA; for channel 2, the output voltage

is adjustable from 0.6V to VIN. Internal synchronous

0.35Ω, 1.2A/0.7A power switches provide high efficiency

without the need for external Schottky diodes.

A user selectable mode input is provided to allow the user

to trade-off noise ripple for low power efficiency. Burst

Mode® operation provides high efficiency at light loads,

while Pulse Skip Mode provides low noise ripple at light

loads.

To further maximize battery run time, the P-channel

MOSFETs are turned on continuously in dropout (100%

duty cycle), and both channels draw a total quiescent

current of only 40µA. In shutdown, the device draws <1µA.

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners. Burst Mode is a registered

trademark of Linear Technology Corporation. Protected by U.S. Patents including 5481178,

6580258, 6304066, 6127815, 6498466, 6611131.

TYPICAL APPLICATIO

VIN

2.8V TO 5.5V

10µF

VOUT2

2.5V

400mA

4.7µH

68pF

RUN2 VIN RUN1

MODE/SYNC

POR

LTC3548-2

SW2

SW1

100k

RESET

2.2µH

VOUT1

1.8V

800mA

887k

4.7µF

280k

VFB2

VOUT1

GND

10µF

35482 F01

Figure 1. 2.5V/1.8V at 400mA/800mA Step-Down Regulators

100

95

90

85

80

75

70

65

60

1

Efficiency and Power Loss

vs Load Current

1000

EFFICIENCY

100

POWER LOSS

10

VIN = 3.6V

VOUT = 1.8V

1

Burst Mode OPERATION

CHANNEL 1

NO LOAD ON CHANNEL 2

0.1

10

100

1000

LOAD CURRENT (mA)

35482 F01b

35482fa

1

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