Rainbow-electronics MAX1644 Bedienungsanleitung PDF herunterladen

General Description

The MAX1644 constant-off-time, PWM step-down DC-

DC converter is ideal for use in applications such as PC

cards, CPU daughter cards, and desktop computer

bus-termination boards. The device features internal

synchronous rectification for high efficiency and

reduced component count. It requires no external

Schottky diode. The internal 0.10Ω PMOS power switch

and 0.10Ω NMOS synchronous-rectifier switch easily

deliver continuous load currents up to 2A. The

MAX1644 produces a preset +3.3V or +2.5V output

voltage or an adjustable output from +1.1V to V

. It

achieves efficiencies as high as 95%.

The MAX1644 uses a unique current-mode, constant-

off-time, PWM control scheme, which includes an Idle

Mode™ to maintain high efficiency during light-load

operation. The programmable constant-off-time archi-

tecture sets switching frequencies up to 350kHz, allow-

ing the user to optimize performance trade-offs

between efficiency, output switching noise, component

size, and cost. The device also features an adjustable

soft-start to limit surge currents during start-up, a 100%

duty cycle mode for low-dropout operation, and a low-

power shutdown mode that disconnects the input from

the output and reduces supply current below 1µA. The

MAX1644 is available in a 16-pin SSOP package.

Applications

+5V to +3.3V/+2.5V Conversion

CPU I/O Supply

+3.3V PC Card and CardBus Applications

Notebook and Subnotebook Computers

Desktop Bus-Termination Boards

CPU Daughter Card Supply

Features

♦ ±1% Output Accuracy

♦ 95% Efficiency

♦ Internal PMOS and NMOS Switches

70mΩ On-Resistance at V

= +4.5V

100mΩ On-Resistance at V

= +3V

♦ Output Voltage

+3.3V or +2.5V Pin-Selectable

+1.1V to V

Adjustable

♦ +3V to +5.5V Input Voltage Range

♦ 360µA (max) Operating Supply Current

♦ < 1µA Shutdown Supply Current

♦ Programmable Constant-Off-Time Operation

♦ 350kHz (max) Switching Frequency

♦ 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

♦ 16-Pin SSOP Package

MAX1644

2A, Low-Voltage, Step-Down Regulator with

Synchronous Rectification and Internal Switches

SHDN LX

PGND

FBSEL

REF

GND

TOP VIEW

MAX1644

SSOP

COMP

TOFF

19-1457; Rev 2; 3/02

PART

MAX1644EAE -40°C to +85°C

TEMP RANGE PIN-PACKAGE

16 SSOP

Pin Configuration

Ordering Information

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

Typical Operating Circuit

TOFF

COMP

FBSEL

SHDN

PGND

GND

REF

MAX1644

TOFF

OUTPUT

+1.1V TO

INPUT

+3V TO

+5.5V

________________________________________________________________ Maxim Integrated Products 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.

EVALUATION KIT

AVAILABLE

1 2 3 4 5 6 ... 10 11

Inhaltsverzeichnis

Seite 1 - AVAILABLE

General DescriptionThe MAX1644 constant-off-time, PWM step-down DC-DC converter is ideal for use in applications such as PCcards, CPU daughter cards,

Seite 2 - ELECTRICAL CHARACTERISTICS

MAX16442A Low-Voltage, Step-Down Regulator withSynchronous Rectification and Internal Switches10 _____________________________________________________

Seite 3

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses arei

Seite 4 - (Circuit of Figure 1, T

MAX16442A, Low-Voltage, Step-Down Regulator withSynchronous Rectification and Internal Switches2 _____________________________________________________

Seite 5 - Pin Description

MAX16442A, Low-Voltage, Step-Down Regulator withSynchronous Rectification and Internal Switches_______________________________________________________

Seite 6 - Summing Comparator

MAX16442A, Low-Voltage, Step-Down Regulator withSynchronous Rectification and Internal Switches4 _____________________________________________________

Seite 7 - Power Dissipation

MAX16442A, Low-Voltage, Step-Down Regulator withSynchronous Rectification and Internal Switches_______________________________________________________

Seite 8 - Setting the Output Voltage

MAX16442A, Low-Voltage, Step-Down Regulator withSynchronous Rectification and Internal Switches6 _____________________________________________________

Seite 9 - Setting the AC Loop Gain

Synchronous RectificationIn a step-down regulator without synchronous rectifica-tion, an external Schottky diode provides a path for cur-rent to flow

Seite 10 - Circuit Layout and Grounding

MAX1644__________________Design ProcedureFor typical applications, use the recommended compo-nent values in Table 1. For other applications, take thef

Seite 11 - Package Information

fPWM= switching frequency in PWM mode (IOUT> 0.2A)Select RTOFFaccording to the formula:RTOFF= (tOFF- 0.07µs) (150kΩ / 1.26µs)Recommended values for

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Rainbow-electronics MAX1644 Bedienungsanleitung

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Inhaltsverzeichnis

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