Rainbow Electronics MAX1644 - Manual

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 0.10
Ω PMOS power switch
and 0.10
Ω 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.
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
Features
♦ ±1% Output Accuracy
♦ 95% Efficiency
♦ Internal PMOS and NMOS Switches
70m
Ω On-Resistance at V
IN = +4.5V
100m
Ω 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
MAX1644
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
SHDN LX
PGND
LX
PGND
V CC
FBSEL
REF
GND
TOP VIEW
MAX1644
SSOP
IN
LX
COMP
IN
SS
TOFF
FB
19-1457; Rev 2; 3/02
PART
MAX1644EAE -40°C to +85°C
TEMP RANGE PIN-PACKAGE
16 SSOP
Pin Configuration
Ordering Information
Idle Mode is a trademark of Maxim Integrated Products, Inc.
Typical Operating Circuit
TOFF
COMP
V CC
FBSEL
SHDN
IN
PGND
GND
REF
SS
LX
FB MAX1644
R TOFF
OUTPUT
+1.1V TO
V
IN
INPUT
+3V TO
+5.5V
________________________________________________________________ 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.
EVALUATION KIT
AVAILABLE