Rainbow-electronics MAX8742 Instrukcja Użytkownika Pobierz pdf (Strona 1)

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

General Description

The MAX8741/MAX8742 are buck-topology, step-down,

switch-mode, power-supply controllers that generate

logic-supply voltages in battery-powered systems. These

high-performance, dual/triple-output devices include on-

board power-up sequencing, power-good signaling with

delay, digital soft-start, secondary winding control, low-

dropout circuitry, internal frequency-compensation net-

works, and automatic bootstrapping.

Up to 97% efficiency is achieved through synchronous

rectification and Maxim’s proprietary Idle Mode™ control

scheme. Efficiency is greater than 80% over a 1000:1

load-current range, which extends battery life in system

suspend or standby mode. Excellent dynamic response

corrects output load transients within five clock cycles.

Strong 1A on-board gate drivers ensure fast external

n-channel MOSFET switching.

These devices feature a logic-controlled and synchroniz-

able, fixed-frequency, pulse-width-modulation (PWM)

operating mode. This reduces noise and RF interference

in sensitive mobile communications and pen-entry appli-

cations. Asserting the SKIP pin enables fixed-frequency

mode, for lowest noise under all load conditions.

The MAX8741/MAX8742 include two PWM regulators,

adjustable from 2.5V to 5.5V with fixed 5.0V and 3.3V

modes. All these devices include secondary feedback

regulation, and the MAX8742 contains a 12V/120mA lin-

ear regulator. The MAX8741 includes a secondary feed-

back input (SECFB), plus a control pin (STEER) that

selects which PWM (3.3V or 5V) receives the secondary

feedback signal. SECFB provides a method for adjusting

the secondary winding voltage regulation point with an

external resistor-divider, and is intended to aid in creating

auxiliary voltages other than fixed 12V.

The MAX8741/MAX8742 contain internal output overvolt-

age- and undervoltage-protection features.

________________________Applications

Notebook and Subnotebook Computers

PDAs and Mobile Communicators

Desktop CPU Local DC-DC Converters

Features

♦ 97% Efficiency

♦ 4.2V to 30V Input Range

♦ 2.5V to 5.5V Dual Adjustable Outputs

♦ Selectable 3.3V and 5V Fixed or Adjustable

Outputs (Dual Mode™)

♦ 12V Linear Regulator

♦ Adjustable Secondary Feedback (MAX8741)

♦ 5V/50mA Linear-Regulator Output

♦ Precision 2.5V Reference Output

♦ Programmable Power-Up Sequencing

♦ Power-Good (RESET) Output

♦ Output Overvoltage Protection

♦ Output Undervoltage Shutdown

♦ 333kHz/500kHz Low-Noise, Fixed-Frequency

Operation

♦ Low-Dropout, 98% Duty-Factor Operation

♦ 2.5mW Typical Quiescent Power (12V Input,

Both SMPSs On)

♦ 4µA Typical Shutdown Current

MAX8741/MAX8742

500kHz Multi-Output Power-Supply Controllers

with High Impedance in Shutdown

________________________________________________________________ Maxim Integrated Products 1

LINEAR

12V

LINEAR

POWER-UP

SEQUENCE

POWER-

GOOD

3.3V

SMPS

RESETON/OFF

5V (RTC)

3.3V

INPUT

12V

Functional Diagram

19-3262; Rev 0; 4/04

Ordering Information

Idle Mode is a trademark of Maxim Integrated Products, Inc.

Dual Mode is a trademark of Maxim Integrated Products, Inc.

Pin Configurations appear at end of data sheet.

PART

TEMP RANGE

PIN-PACKAGE

MAX8741EAI

-40°C to +85°C

28 SSOP

MAX8741ETJ

-40°C to +85°C

32 Thin QFN 5m m x 5m m

MAX8742EAI

-40°C to +85°C

28 SSOP

MAX8742ETJ

-40°C to +85°C

32 Thin QFN 5m m x 5m m

1 2 3 4 5 6 ... 32 33

MAX8741/MAX8742 1

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Strona 1 - MAX8741/MAX8742

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Package Information (continued)(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outl

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MAX8741/MAX8742500kHz Multi-Output Power-Supply Controllerswith High Impedance in ShutdownMaxim cannot assume responsibility for use of any circuitry

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5V LOAD-TRANSIENT RESPONSEMAX8741/42 toc1110V05A0ILX55A/divVLX510V/div5V OUTPUT5OmV/divAC-COUPLED20µs/divVIN = 8V, IOUT = 1A TO 5A3.3V LOAD-TRANSIENT

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