Miniature, Low-Voltage,

Precision Step-Down Controller

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9

The pulse-width-modulation (PWM) controller consists

of a multi-input PWM comparator, high-side and low-

side gate drivers, and logic. It uses a 200kHz/300kHz

synchronizable oscillator. The MAX1637 contains fault-

protection circuits that monitor the PWM output for

undervoltage and overvoltage. It includes a 1.100V pre-

cision reference. The circuit blocks are powered from

gate driver, but provides indirect power to the high-

side-switch gate driver via an external diode-capacitor

boost circuit.

REF

IC

POWER

200kHz

TO

300kHz

OSC

PWM

LOGIC

3.15V TO 5.5V

REF

SHDN

SYNC

DL

PGND

LX

DH

BST

SKIP

CSH

CSL

FB

CC

REF

GND

+

60kHz

LP FILTER

SHUTDOWN

CONTROL

1.1V

REF.

ERROR

INTEGRATOR

+

-

-

-

-

MAX1637

gm

OVERVOLTAGE

FAULT

UNDER-

VOLTAGE

FAULT

OFF

SLOPE

COMPENSATION

Figure 2. Functional Diagram