MAX747CPD 데이터 시트보기 (PDF) - Maxim Integrated

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MAX747CPD

High-efficiency, PWM, step-down P-channel DC-DC controller

Maxim Integrated 

High-Efficiency PWM, Step-Down

P-Channel DC-DC Controller

LBI

LOW-BATTERY

COMPARATOR

LBO

+2V

N

REFERENCE

REF

OUT

60k

CC

40k

FB

DUAL-MODE

COMPARATOR

EXT

V+

100kHz

OSCILLATOR

ERROR

AMPLIFIER

EXT

CONTROL

PWM

COMPARATOR

SHDN

100mV

AV+

CS

SS

SOFT-START

CIRCUITRY

CURRENT-SENSE

AMPLIFIER

Σ

SLOPE

VRAMP

COMPENSATION

RAMP

CURRENT-LIMIT

COMPARATOR

50mV

IDLE-MODE

COMPARATOR

AGND

Figure 2. Block Diagram

The Oscillator and EXT Control

The switching frequency is nominally 100kHz and the

duty cycle varies from 5% to 96%, depending on the

input/output voltage ratio. EXT, which provides the gate

drive for the external P-FET, is switched between V+

and GND at the switching frequency. EXT is controlled

by a unique two-comparator control scheme composed

of a PWM comparator and an idle-mode comparator

GND

(Figure 2). The PWM comparator determines the cycle-

by-cycle peak current with heavy loads, and the

light-load comparator sets the light-load peak current.

As VOUT begins to drop, EXT goes low and remains low

until both comparators trip. With heavy loads, the idle-

mode comparator trips quickly, and the PWM control

comparator determines the EXT on-time; with light

loads, the idle-mode comparator sets the EXT on-time.

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