19-1457; Rev 3; 8/05
KIT
ATION
EVALU
BLE
AVAILA
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
General Description
The MAX1644 constant-off-time, PWM step-down DC-
DC converter is ideal for use in applications such as PC
cards, CPU daughter cards, and desktop computer
bus-termination boards. The device features internal
synchronous rectification for high efficiency and
reduced component count. It requires no external
Schottky diode. The internal 0.10Ω PMOS power switch
and 0.10Ω NMOS synchronous-rectifier switch easily
deliver continuous load currents up to 2A. The
MAX1644 produces a preset +3.3V or +2.5V output
voltage or an adjustable output from +1.1V to V
IN
. It
achieves efficiencies as high as 95%.
The MAX1644 uses a unique current-mode, constant-
off-time, PWM control scheme, which includes an Idle
Mode™ to maintain high efficiency during light-load
operation. The programmable constant-off-time archi-
tecture sets switching frequencies up to 350kHz, allow-
ing the user to optimize performance trade-offs
between efficiency, output switching noise, component
size, and cost. The device also features an adjustable
soft-start to limit surge currents during start-up, a 100%
duty cycle mode for low-dropout operation, and a low-
power shutdown mode that disconnects the input from
the output and reduces supply current below 1µA. The
MAX1644 is available in a 16-pin SSOP package.
♦
±1% Output Accuracy
♦
95% Efficiency
♦
Internal PMOS and NMOS Switches
70mΩ On-Resistance at V
IN
= +4.5V
100mΩ On-Resistance at V
IN
= +3V
♦
Output Voltage
+3.3V or +2.5V Pin-Selectable
+1.1V to V
IN
Adjustable
♦
+3V to +5.5V Input Voltage Range
♦
360µA (max) Operating Supply Current
♦
< 1µA Shutdown Supply Current
♦
Programmable Constant-Off-Time Operation
♦
350kHz (max) Switching Frequency
♦
Idle Mode Operation at Light Loads
♦
Thermal Shutdown
♦
Adjustable Soft-Start Inrush Current Limiting
♦
100% Duty Cycle During Low-Dropout Operation
♦
Output Short-Circuit Protection
♦
16-Pin SSOP Package
Features
MAX1644
Applications
+5V to +3.3V/+2.5V Conversion
CPU I/O Supply
+3.3V PC Card and CardBus Applications
Notebook and Subnotebook Computers
Desktop Bus-Termination Boards
CPU Daughter Card Supply
Ordering Information
PART
MAX1644EAE
MAX1644EAE+
TEMP RANGE
40°C to +85°C
40°C to +85°C
PIN-PACKAGE
16 SSOP
16 SSOP
+Denotes
lead-free package.
Pin Configuration
TOP VIEW
OUTPUT
+1.1V TO
V
IN
SHDN 1
IN 2
LX 3
IN 4
SS 5
16 LX
15 PGND
14 LX
Typical Operating Circuit
INPUT
+3V TO
+5.5V
IN
LX
MAX1644
FB
V
CC
FBSEL
SHDN
COMP
TOFF
R
TOFF
GND
REF
SS
PGND
MAX1644
13 PGND
12 V
CC
11 FBSEL
10 REF
9
GND
COMP 6
TOFF 7
FB 8
SSOP
Idle Mode is a trademark of Maxim Integrated Products, Inc.
A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.
________________________________________________________________
Maxim Integrated Products
1
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.
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
