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MAX1843

2.7A, 1MHz, Low-Voltage, Step-Down Regulator with

Internal Synchronous Rectification in QFN Package

________________________________________________________________ Maxim Integrated Products 1

19-1986; Rev 1; 3/02

General Description

The MAX1843 constant-off-time, pulse-width modulated

(PWM) step-down DC-DC converter is ideal for use in 5V

and 3.3V to low-voltage conversion necessary in note-

book and subnotebook computers. This device features

an internal PMOS power switch and internal synchronous

rectification for high efficiency and reduced component

count. An external Schottky diode is not required. The

internal 90mΩ power switch and 70mΩ NMOS synchro-

nous-rectifier switch easily deliver continuous load cur-

rents up to 2.7A. The MAX1843 produces a preset +2.5V,

+1.8V, or +1.5V output voltage or an adjustable output

from +1.1V to V

. It achieves efficiencies as high as

95%.

The MAX1843 uses a unique current-mode, constant-off-

time, PWM control scheme, which includes Idle Mode™

to maintain high efficiency during light-load operation.

The programmable constant-off-time architecture sets

switching frequencies up to 1MHz, allowing the user to

optimize performance trade-offs between efficiency, out-

put switching noise, component size, and cost. The

MAX1843 features an adjustable soft-start to limit surge

currents during startup, a 100% duty-cycle mode for low

dropout operation, and a low-power shutdown mode that

disconnects the input from the output and reduces sup-

ply current below 1µA. The MAX1843 is available in a 28-

pin QFN package with an exposed backside pad.

Applications

5V or 3.3V to Low-Voltage Conversion

CPU I/O Ring

Chipset Supplies

Notebook and Subnotebook Computers

Features

♦ ±1% Output Accuracy

♦ Up to 1MHz Switching Frequency

♦ 95% Efficiency

♦ Internal PMOS/NMOS Switches

90mΩ/70mΩ On-Resistance at V

= +4.5V

110mΩ/80mΩ On-Resistance at V

= +3V

♦ Output Voltage

+2.5V, +1.8V, or +1.5V Pin Selectable

+1.1V to V

Adjustable

♦ +3V to +5.5V Input Voltage Range

♦ 350µA Operating Supply Current

♦ <1µA Shutdown Supply Current

♦ Programmable Constant-Off-Time Operation

♦ Idle Mode Operation at Light Loads

♦ Thermal Shutdown

♦ Adjustable Soft-Start Inrush Current Limiting

♦ 100% Duty Cycle During Low-Dropout Operation

♦ Output Short-Circuit Protection

♦ 28-Pin QFN Package

PART TEMP RANGE PIN-PACKAGE

Ordering Information

Idle Mode is a trademark of Maxim Integrated Products.

EVALUATION KIT

AVAILABLE

MAX1843EGI -40°C to +85°C 28 QFN

MAX1843

2526

28 22

2324

10 11 12 13 14

REF

TOFF

N.C.

GND

N.C.

COMP

N.C.

PGND

FBSEL

PGND

QFN

TOP VIEW

N.C.

SHDN

Pin Configuration

TOFF

COMP

FBSEL

SHDN

PGND

GND

REF

MAX1843

OUTPUT

+1.1V TO

INPUT

+3V TO

+5.5V

0.01µF

1µF

2.2µF

470pF

10Ω

Typical Configuration

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.

1 2 3 4 5 6 ... 12 13

Inhaltsverzeichnis

Seite 1 - AVAILABLE

MAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN Package_____________________________________________

Seite 2 - ELECTRICAL CHARACTERISTICS

MAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN Package10 __________________________________________

Seite 3

MAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN Package_____________________________________________

Seite 4 - MAX1843 toc06

32L QFN .EPSMAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withSynchronous Rectification in QFN Package12 _______________________________________

Seite 5 - MAX1843 toc07

2.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN PackageMAX1843Maxim cannot assume responsibility for use of

Seite 6 - Pin Description

MAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN Package2 ___________________________________________

Seite 7

MAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN Package_____________________________________________

Seite 8

Typical Operating Characteristics(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)0.001 0.01 0.1 1 10EFFICIENCY vs. OUTPUT CURRENT(VIN = +5.0

Seite 9 - Design Procedure

MAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN Package_____________________________________________

Seite 10 - Integrator Amplifier

MAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN Package6 ___________________________________________

Seite 11 - Chip Information

MAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN Package_____________________________________________

Seite 12 - Package Information

MAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN Package8 ___________________________________________

Seite 13

MAX18432.7A, 1MHz, Low-Voltage, Step-Down Regulator withInternal Synchronous Rectification in QFN Package_____________________________________________

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