3A, 1MHz, Low-Voltage, Step-Down Regulators with

Synchronous Rectification and Internal Switches

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7

lation comparator turns the PMOS switch on at the end

of each off-time, keeping the device in continuous-con-

duction mode. The PMOS switch remains on until the

output is in regulation or the current limit is reached.

When the PMOS switch turns off, it remains off for the

under short-circuit conditions, the PMOS switch

Idle Mode

Under light loads, the devices improve efficiency by

switching to a pulse-skipping Idle Mode. Idle Mode

operation occurs when the current through the PMOS

switch is less than the Idle Mode threshold current. Idle

Mode forces the PMOS to remain on until the current

through the switch reaches the Idle Mode threshold,

thus minimizing the unnecessary switching that

degrades efficiency under light loads. In Idle Mode, the

470pF

2.2

µF

1

µF

10

Ω

FBSEL

FEEDBACK

SELECTION

CURRENT

SENSE

PWM LOGIC

AND

DRIVERS

IN

FB

3.0V TO 5.5V

LX

CERAMIC

PGND

TOFF

GND

NOTE: HEAVY LINES DENOTE HIGH-CURRENT PATHS.

REF

REF

SUMMING

COMPARATOR

REF

REF

COMP

SKIP

SHDN

TIMER

CURRENT

SENSE

DIGITAL

SOFT-START

MAX1830

MAX1831

Figure 2. Functional Diagram

TOFF

COMP

FBSEL

SHDN

IN

PGND

GND

REF

MAX1830

LX

FB

MAX1830

MAX1831

1

µF

L

1.5

µF

2.2

µF

470pF

10

Ω

INPUT

OUTPUT

MAX1831

SUMIDA

CDRH-6D28

120

µF, 4V

Panasonic SP

22

µF,

6.3V X5R

Figure 1. Typical Circuit