19-1436; Rev 2; 3/02
NUAL
KIT MA
ATION
EVALU
BLE
AVAILA
3A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
________________________Applications
5V to 3.3V Conversion
Notebook Computer CPU I/O Supply
Desktop Computer Bus-Termination Supply
____________________________Features
o ±1% Output Accuracy, Including Line and Load
Regulation
o 94% Efficiency
o Internal Switches
55mΩ PMOS Power Switch
60mΩ NMOS Synchronous-Rectifier Switch
o Guaranteed 3A Load Capability
o Minimal External Components
o Pin-Selectable Fixed 3.3V, 2.5V, or
Adjustable (1.1V to 3.8V) Output Voltage
o 4.5V to 5.5V Input Voltage Range
o 400µA (typ) Supply Current
o <1µA Shutdown Supply Current
o Constant-Off-Time PWM Operation
o Switching Frequencies Up to 350kHz
o Idle Mode™ Operation at Light Loads
o Thermal Shutdown Protection
o Available in 20-Pin SSOP
CPU Daughter Card Supply
Ordering Information
DSP Supply
PART
MAX1623EAP
TEMP RANGE
PIN-PACKAGE
-40°C to +85°C
20 SSOP
Pin Configuration
Typical Operating Circuit
5V
INPUT
2.5V
OUTPUT
IN
LX
TOP VIEW
LX 1
20 LX
IN 2
VCC
PGND
FBSEL
SHDN
19 PGND
LX 3
MAX1623
18 LX
IN 4
17 PGND
LX 5
FB
MAX1623
IN 6
16 LX
15 PGND
SHDN 7
TOFF
COMP
GND
REF
14 VCC
FBSEL 8
13 COMP
TOFF 9
12 REF
FB 10
11 GND
SSOP
Idle Mode is a trademark of Maxim Integrated Products.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1
MAX1623
General Description
The MAX1623 switch-mode buck regulator with synchronous rectification provides local CPU and bus-termination power in notebook and desktop computers.
An internal 55mΩ (typ), 3A PMOS power switch and
60mΩ (typ), 3A NMOS synchronous-rectifier switch
deliver continuous load currents up to 3A from a 5V
supply with 95% typical efficiency. Output accuracy is
±1%, including line and load regulation.
The MAX1623 features constant-off-time, current-mode
pulse-width-modulation (PWM) control with switching
frequencies as high as 350kHz. An external resistor at
the TOFF pin sets the off-time, allowing optimum design
flexibility in terms of switching frequency, output switching noise, and inductor size. This device is available in
a space-saving 20-pin SSOP package.
