19-1955; Rev 2; 1/03
Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
General Description
Features
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.
o Ultra-High Efficiency
o Accurate Current-Limit Option
o Quick-PWM™ with 100ns Load-Step Response
o 1% V Accuracy over Line and Load
OUT
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
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.
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
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.
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
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.
MAX1845EEI
-40°C to +85°C
28 QSOP
36 Thin QFN
6mm ✕ 6mm
MAX1845ETX
-40°C to +85°C
Applications
Minimal Operating Circuit
Notebook Computers
5V INPUT
BATTERY
CPU Core Supplies
4.5V TO 28V
V
V
V+
DD
Chipset/RAM Supply as Low as 1V
1.8V and 2.5V I/O Supplies
UVP
OVP
CC
MAX1845EEI
ILIM1
ILIM2
ON1
ON2
BST1
DH1
LX1
BST2
DH2
LX2
OUTPUT1
1.8V
OUTPUT2
2.5V
DL1
DL2
CS2
TON
CS1
OUT1
PGOOD
REF
OUT2
SKIP
FB2
FB1
GND
Pin Configurations appear at end of data sheet.
Quick-PWM and Dual Mode are trademarks of Maxim Integrated
Products.
________________________________________________________________ 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.