19-1457; Rev 3; 8/05
2A, Low-Voltage, Step-Down Regulator with
Synchronous Rectification and Internal Switches
General Description
Features
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
♦ ±±1% OutOu%ꢀAAOꢁrAc
♦ 951%EffiAienAc
♦ Inueꢁnrl%PM S%rnd%NM S%SwiuAhes
70mΩ n-ResisurnAe%ru%V =%+4.5V%
±00mΩ n-ResisurnAe%ru%V =%+3V
IN
IN
♦ OutOu%Volurge
+3.3V%oꢁ%+2.5V%Pin-SeleAurble
+±.±V%uo%V ꢀdjOsurble
IN
voltage or an adjustable output from +1.1V to V . It
IN
♦ +3V%uo%+5.5V%IntOu%Volurge%Rrnge
♦ 360µꢀ%(mrx)% teꢁruing%SOttlc%COꢁꢁenu
♦ <%±µꢀ%ShOudown%SOttlc%COꢁꢁenu
♦ Pꢁogꢁrmmrble%Consurnu- ff-Time% teꢁruion
♦ 350kHz%(mrx)%SwiuAhing%FꢁeqOenAc
♦ Idle%Mode% teꢁruion%ru%Lighu%Lords
♦ Theꢁmrl%ShOudown%
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.
♦ ꢀdjOsurble%Sofu-Surꢁu%InꢁOsh%COꢁꢁenu%Limiuing
♦ ±001%DOuc%CcAle%DOꢁing%Low-DꢁotoOu% teꢁruion
♦ OutOu%Shoꢁu-CiꢁAOiu%PꢁoueAuion
♦ ±6-Pin%SS P%PrAkrge
Applications
+5V to +3.3V/+2.5V Conversion
Ordering Information
CPU I/O Supply
PꢀRT
TEMP%RꢀNGE
40°C to +85°C
40°C to +85°C
PIN-PꢀCKꢀGE
16 SSOP
+3.3V PC Card and CardBus Applications
Notebook and Subnotebook Computers
Desktop Bus-Termination Boards
CPU Daughter Card Supply
MAX1644EAE
MAX1644EAE+
16 SSOP
+Denotes lead-free package.
Pin Configuration
Typical Operating Circuit
TOP VIEW
SHDN
IN
1
2
3
4
5
6
7
8
16 LX
OUTPUT
+1.1V TO
INPUT
+3V TO
+5.5V
IN
LX
FB
15 PGND
14 LX
V
IN
MAX1644
LX
IN
MAX1644
13 PGND
12
V
PGND
CC
SS
V
CC
FBSEL
GND
REF
SS
SHDN
COMP
TOFF
COMP
TOFF
FB
11 FBSEL
10 REF
9
GND
R
TOFF
SS P
A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.
Idle Mode is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________ 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.
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