19-1457; Rev 3; 8/05
KIT
ATION
EVALU
E
AILABL
AV
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
The MAX1644 constant-off-time, PWM step-down DCDC 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 VIN. It
achieves efficiencies as high as 95%.
The MAX1644 uses a unique current-mode, constantoff-time, PWM control scheme, which includes an Idle
Mode™ to maintain high efficiency during light-load
operation. The programmable constant-off-time architecture sets switching frequencies up to 350kHz, allowing 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 lowpower 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.
Applications
Features
♦ ±1% Output Accuracy
♦ 95% Efficiency
♦ Internal PMOS and NMOS Switches
70mΩ On-Resistance at VIN = +4.5V
100mΩ On-Resistance at VIN = +3V
♦ Output Voltage
+3.3V or +2.5V Pin-Selectable
+1.1V to VIN 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
Ordering Information
+5V to +3.3V/+2.5V Conversion
CPU I/O Supply
PART
+3.3V PC Card and CardBus Applications
Notebook and Subnotebook Computers
TEMP RANGE
PIN-PACKAGE
MAX1644EAE
Desktop Bus-Termination Boards
CPU Daughter Card Supply
40°C to +85°C
16 SSOP
MAX1644EAE+
40°C to +85°C
16 SSOP
+Denotes lead-free package.
Pin Configuration
Typical Operating Circuit
TOP VIEW
INPUT
+3V TO
+5.5V
IN
LX
MAX1644 FB
VCC
OUTPUT
+1.1V TO
VIN
PGND
16 LX
IN 2
15 PGND
14 LX
LX 3
IN 4
MAX1644
GND
COMP 6
REF
SS
13 PGND
12 VCC
SS 5
FBSEL
SHDN
COMP
TOFF
SHDN 1
TOFF 7
11 FBSEL
10 REF
9
FB 8
GND
RTOFF
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
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
MAX1644
General Description
