soft-start when coming out of undervoltage lockout

(UVLO) or thermal-overload protection.

Undervoltage Lockout (UVLO)

assume that the supply voltage is too low to provide a

valid output voltage, and the UVLO circuit inhibits

abled and the soft-start sequence begins.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipa-

tion and protects the IC from damage in case of an

overload or short-circuit condition. When the IC junction

down. The part turns on again after the junction temper-

ature cools by 20°C. This results in a pulsed output dur-

ing continuous thermal-overload conditions.

Smallest 1A, 1.4MHz Step-Down Regulators

10

______________________________________________________________________________________

PWM

LOGIC BLOCK

PMOS

CURRENT SENSE

VOLTAGE

CLAMP

NMOS

CURRENT LIMIT

SLOPE

COMP

CHIP

ENABLE

REFERENCE

READY

UNDERVOLTAGE

LOCK OUT

FEEDBACK

SELECT

VOLTAGE

MARGINING

SOFT-START

REFERENCE

BIAS

MAX1974

ONLY

POK

IN

LX

PGND

PWM

COMPARATOR

ERROR

AMP

1.4MHz

OSCILLATOR

IN

GND

SS

COMP

OUT

FB

CTL1

CTL2

ON

MAX1973

ONLY

MAX1974

ONLY

Σ

MAX1973

MAX1974

Figure 1. Functional Diagram