MAX1572(2003) 查看數據表（PDF） - Maxim Integrated

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MAX1572
(Rev.:2003)

800mA, 2MHz, PWM DC-to-DC Step-Down Converter with RESET

Maxim Integrated 

800mA, 2MHz, PWM DC-to-DC

Step-Down Converter with RESET

VOUT

(VOLTAGE POSITIONING)

VOUT

(CONVENTIONAL)

IOUT

Figure 2. Load Transient Response, With and Without Voltage

Positioning

+1

CHANGE IN

OUTPUT 0

VOLTAGE (%)

VIN = 3.6V

NORMAL OPERATION

FORCED-PWM

VIN = 5.5V

-1

VIN = 2.6V

-2

0

200

400

600

800

LOAD CURRENT (mA)

Figure 3. Voltage-Positioning Load Line

Soft-Start

Soft-start is used to prevent input-current overshoot dur-

ing startup. For most applications using a 10µF output

capacitor, connect a 1000pF capacitor from SS to GND.

If a larger output capacitor is used, then use the follow-

ing formula to find the value of the soft-start capacitor

needed to prevent input-current overshoot:

CSS = COUT /104

During soft-start, the output voltage rises from 0 to

VOUT(nom) with a time constant equal to CSS times

100kΩ (see the Typical Operating Characteristics).

170ms RESET

RESET is an open-drain output with an internal 14kΩ

pullup resistor to OUT. During startup, RESET is held low

until 200ms (typ) after the output voltage reaches 90% of

its nominal regulation voltage. When the output voltage

drops below 90% of its nominal regulation voltage,

RESET pulls low again. See the Typical Operating

Characteristics section for RESET waveforms during

startup and shutdown.

Applications Information

Inductor Selection

A 2.2µH inductor with a saturation current of at least 1A

is recommended for full-load (800mA) applications. For

lower load currents, the inductor current rating may be

reduced. For most applications, use an inductor with a

current rating 1.25 times the maximum required output

current. For maximum efficiency, the inductor’s DC

resistance should be as low as possible. See Table 2

for recommended inductors and manufacturers.

Capacitor Selection

Ceramic 10µF input and output capacitors are recom-

mended for most applications. For output voltages

below 1.5V, output capacitance should be increased to

22µF. For best stability over a wide temperature range,

use capacitors with an X5R or better dielectric.

ABATT Input Filter

In normal applications, an RC filter on ABATT keeps

power-supply noise from entering the IC. Connect a

10Ω resistor between BATT and ABATT and connect a

0.1µF capacitor from ABATT to GND.

PC Board Layout and Routing

Due to fast-switching waveforms and high-current

paths, careful PC board layout is required. An evalua-

tion kit (MAX1572EVKIT) is available to speed design.

When laying out a board, minimize trace lengths

between the IC, the inductor, the input capacitor, and the

output capacitor. Keep these traces short, direct, and

wide. Keep noisy traces, such as the LX node trace,

away from OUT. The input bypass capacitors should be

placed as close to the IC as possible. Connect PGND

and GND directly to the exposed paddle underneath the

IC. The ground connections of the input and output

capacitors should be as close together as possible.

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