19-1955; Rev 2; 1/03
KIT
ATION
EVALU
BLE
AVAILA
Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
MAX1845
General Description
Features
o
Ultra-High Efficiency
o
Accurate Current-Limit Option
o
Quick-PWM™ with 100ns Load-Step Response
o
1% V
OUT
Accuracy over Line and Load
o
Dual Mode™ Fixed 1.8V/1.5V/Adj or 2.5V/Adj Outputs
o
Adjustable 1V to 5.5V Output Range
o
2V to 28V Battery Input Range
o
200/300/420/540kHz Nominal Switching Frequency
o
Adjustable Overvoltage Protection
o
1.7ms Digital Soft-Start
o
Drives Large Synchronous-Rectifier FETs
o
Power-Good Window Comparator
o
2V ±1% Reference Output
The MAX1845 is a dual PWM controller configured for
step-down (buck) topologies that provides high efficien-
cy, excellent transient response, and high DC output
accuracy necessary for stepping down high-voltage bat-
teries to generate low-voltage chipset and RAM power
supplies in notebook computers. The CS_ inputs can be
used with low-side sense resistors to provide accurate
current limits or can be connected to LX_, using low-side
MOSFETs as current-sense elements.
The on-demand PWM controllers are free running, con-
stant on-time with input feed-forward. This configuration
provides ultra-fast transient response, wide input-output
differential range, low supply current, and tight load-reg-
ulation characteristics. The MAX1845 is simple and easy
to compensate.
Single-stage buck conversion allows the MAX1845 to
directly step down high-voltage batteries for the highest
possible efficiency. Alternatively, two-stage conversion
(stepping down the 5V system supply instead of the bat-
tery at a higher switching frequency) allows the minimum
possible physical size.
The MAX1845 is intended for generating chipset, DRAM,
CPU I/O, or other low-voltage supplies down to 1V. For a
single-output version, refer to the MAX1844 data sheet.
The MAX1845 is available in 28-pin QSOP and 36-pin
thin QFN packages.
Ordering Information
PART
MAX1845EEI
MAX1845ETX
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
28 QSOP
36 Thin QFN
6mm
✕
6mm
Applications
Notebook Computers
CPU Core Supplies
Chipset/RAM Supply as Low as 1V
1.8V and 2.5V I/O Supplies
5V INPUT
Minimal Operating Circuit
BATTERY
4.5V TO 28V
V
DD
V
CC
ILIM1
ILIM2
ON1
ON2
BST1
OUTPUT1
1.8V
DH1
LX1
DL1
V+
UVP
OVP
MAX1845EEI
BST2
DH2
LX2
DL2
CS2
OUTPUT2
2.5V
TON
CS1
OUT1
PGOOD
OUT2
REF
SKIP
Pin Configurations appear at end of data sheet.
Quick-PWM and Dual Mode are trademarks of Maxim Integrated
Products.
FB1
GND
FB2
________________________________________________________________
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 ]
