Datasheet

MAX1973/MAX1974
soft-start when coming out of undervoltage lockout
(UVLO) or thermal-overload protection.
Undervoltage Lockout (UVLO)
If V
IN
drops below 2.35V (typ), the MAX1973/MAX1974
assume that the supply voltage is too low to provide a
valid output voltage, and the UVLO circuit inhibits
switching. Once V
IN
rises above 2.4V, UVLO is dis-
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
temperature (T
J
) exceeds +170°C, the device shuts
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