19-2142; Rev 1; 9/02
3A, 1MHz, DDR Memory Termination Supply
General Description
Features
The MAX1809 is a reversible energy flow, constant-off-
time, pulse-width modulated (PWM), step-down DC-DC
converter. It is ideal for use in notebook and subnote-
book computers that require 1.1V to 5V active
termination power supplies. This device features an
internal PMOS power switch and internal synchronous
rectifier for high efficiency and reduced component
count. The internal 90mΩ PMOS power switch and
70mΩ NMOS synchronous-rectifier switch easily deliver
continuous load currents up to 3A. The MAX1809 accu-
rately tracks an external reference voltage, produces
o Source/Sink 3A
o ±±1 ꢀuꢁtuꢁ Accurꢂcꢃ
o Ut ꢁo ±MHz Swiꢁching Frequencꢃ
o 931 Efficiencꢃ
o Inꢁernꢂl PMꢀS/NMꢀS Swiꢁches
90mΩ/70mΩ ꢀn-Resisꢁꢂnce ꢂꢁ V = 4.5V
±±0mΩ/80mΩ ꢀn-Resisꢁꢂnce ꢂꢁ V = 3V
IN
IN
o ±.±V ꢁo V Adjusꢁꢂble ꢀuꢁtuꢁ Volꢁꢂge
IN
an adjustable output from 1.1V to V
efficiencies as high as 93%.
and achieves
IN,
o 3V ꢁo 5.5V Intuꢁ Volꢁꢂge Rꢂnge
o <±µA Shuꢁdown Suttlꢃ Currenꢁ
o Progrꢂmmꢂble Consꢁꢂnꢁ-ꢀff-Time ꢀterꢂꢁion
o Thermꢂl Shuꢁdown
The MAX1809 uses a unique current-mode, constant-
off-time, PWM control scheme that allows the output to
source or sink current. This feature allows energy to
return to the input power supply that otherwise would
be wasted. The programmable constant-off-time archi-
tecture sets switching frequencies up to 1MHz, allowing
the user to optimize performance trade-offs between
efficiency, output switching noise, component size, and
cost. The MAX1809 features an adjustable soft-start to
limit surge currents during startup, a 100% duty-cycle
mode for low-dropout operation, and a low-power shut-
down mode that disables the power switches and
reduces supply current below 1µA. The MAX1809 is
available in a 28-pin QFN with an exposed backside
pad, a 28-pin thin QFN, or a 16-pin QSOP.
o Adjusꢁꢂble Sofꢁ-Sꢁꢂrꢁ Inrush Currenꢁ Limiꢁing
o ꢀuꢁtuꢁ Shorꢁ-Circuiꢁ Proꢁecꢁion
Ordering Information
PART
MAX1809EGI*
MAX1809EEE
MAX1809ETI
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 QFN
16 QSOP
28 Thin QFN
*Contact factory for availability.
Applications
DDR Memory Termination
Active Termination Buses
Pin Configurations
TOP VIEW
Typical Operating Circuit
N.C.
IN
PGND
PGND
LX
1
2
3
4
5
6
7
21
20
19
18
17
16
15
V
V
OUT
IN
IN
LX
LX
MAX1809
PGND
GND
IN
LX
MAX1809
V
CC
N.C.
PGND
FB
REF
SS
SHDN
V
CC
SS
V
SET
EXTREF
EXTREF
GND
TOFF
THIN QFN
Pin Configurations continued at end of data sheet.
________________________________________________________________ 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.