MAX1742 Просмотр технического описания (PDF) - Maxim Integrated

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MAX1742

1A/2.7A, 1MHz, Step-Down Regulators with Synchronous Rectification and Internal Switches

Maxim Integrated 

1A/2.7A, 1MHz, Step-Down Regulators with

Synchronous Rectification and Internal Switches

INPUT

CIN = 10μF (MAX1742)

CIN = 33μF (MAX1842)

10Ω

2.2μF

470pF

RTOFF

IN

LX

MAX1742 FB

VCC

PGND

SHDN

COMP

GND

FBSEL

REF

TOFF

SS

L

OUTPUT

COUT = 47μF (MAX1742)

COUT = 150μF (MAX1842)

1μF

0.01μF

VOUT = 2.5V, FBSEL = VCC

VOUT = 1.8V, FBSEL = REF

VOUT = 1.5V, FBSEL = FLOATING

Figure 1. Typical Circuit

FBSEL

0.01μF

SS

FB

470pF

COMP

REF

VIN 10Ω

VCC

2.2μF

SHDN

FEEDBACK

SELECTION

Gm

REF

MAX1742

MAX1842

SUMMING

COMPARATOR

CURRENT

SENSE

SKIP

PWM LOGIC

AND

DRIVERS

IN

10μF

VIN

3.0V TO 5.5V

VOUT

LX

COUT

REF

1μF

REF

GND

TIMER

CURRENT

SENSE

TOFF

RTOFF

PGND

NOTE: HEAVY LINES DENOTE HIGH-CURRENT PATHS.

Figure 2. Functional Diagram

Synchronous Rectification

In a step-down regulator without synchronous rectifica-

tion, an external Schottky diode provides a path for cur-

rent to flow when the inductor is discharging. Replacing

the Schottky diode with a low-resistance NMOS syn-

chronous switch reduces conduction losses and

improves efficiency.

The NMOS synchronous-rectifier switch turns on follow-

ing a short delay after the PMOS power switch turns off,

thus preventing cross conduction or “shoot through.” In

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