Rainbow-electronics MAX887 Manual do Utilizador descarregar pdf

_______________General Description

The MAX887 high-efficiency, step-down DC-DC con-

verter provides an adjustable output from 1.25V to

10.5V. It accepts inputs from 3.5V to 11V and delivers

600mA. Operation to 100% duty cycle minimizes

dropout voltage (300mV typ at 500mA). Synchronous

rectification reduces output rectifier losses, resulting in

efficiency as high as 95%.

Fixed-frequency pulse-width modulation (PWM)

reduces noise in sensitive communications applica-

tions. Using a high-frequency internal oscillator allows

tiny surface-mount components to reduce PC board

area, and eliminates audio-frequency interference. A

SYNC input allows synchronization to an external clock

to avoid interference with sensitive RF and data-

acquisition circuits.

The MAX887 features current-mode operation for supe-

rior load/line-transient response. Cycle-by-cycle current

limiting protects the internal MOSFET and rectifier. A

low-current (2.5µA typ) shutdown mode conserves bat-

tery life.

________________________Applications

Portable Instruments

Cellular Phones and Radios

Personal Communicators

Distributed Power Systems

Computer Peripherals

____________________________Features

♦ 95% Efficiency

♦ 600mA Output Current

♦ Cycle-by-Cycle Current Limiting

♦ Low-Dropout, 100% Duty-Cycle Operation,

300mV at 500mA

♦ Internal 0.6Ω (typ) MOSFET

♦ Internal Synchronous Rectifier

♦ High-Frequency Current-Mode PWM

♦ External SYNC or Internal 300kHz Oscillator

♦ Guaranteed 260kHz to 340kHz Internal Oscillator

Frequency Limits

♦ 2.5µA Shutdown Mode

MAX887

100% Duty Cycle, Low-Noise,

Step-Down, PWM DC-DC Converter

________________________________________________________________

Maxim Integrated Products

V+

SYNC

GND

SHDN

REF

MAX887

TOP VIEW

__________________Pin Configuration

MAX887

REF

165kΩ

100kΩ

0.047µF

2.2µF

47µF

100pF

0.33µF

33µH

V+ LX

GND

SYNC

SHDN

OUT

= 3.3V

OUT

= 1.25V (R1/R2 + 1)

= 3.5V to 11V

OFF

__________Typical Operating Circuit

19-1142 Rev 0; 9/96

PART

MAX887HC/D

MAX887HESA -40°C to +85°C

0°C to +70°C

TEMP. RANGE PIN-PACKAGE

Dice*

8 SO

EVALUATION KIT MANUAL

AVAILABLE

______________Ordering Information

Contact factory for availability. Dice are tested at T

= +25°C.

For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800

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100% Duty Cycle, Low-Noise 1

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Página 1 - 100% Duty Cycle, Low-Noise

_______________General DescriptionThe MAX887 high-efficiency, step-down DC-DC con-verter provides an adjustable output from 1.25V to10.5V. It accepts

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MAX887100% Duty Cycle, Low-Noise, Step-Down, PWM DC-DC Converter10 ___________________________________________________________________________________

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