MAX1845 Datasheet, PDF (1/27 Pages) Maxim Integrated Products – Dual, High-Efficiency, Step-Down Controller with Accurate Current Limit

19-1955; Rev 2; 1/03
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Dual, High-Efficiency, Step-Down
Controller with Accurate Current Limit
General Description
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.
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
PART
MAX1845EEI
MAX1845ETX
Ordering Information
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
OUTPUT1
1.8V
Pin Configurations appear at end of data sheet.
Quick-PWM and Dual Mode are trademarks of Maxim Integrated
Products.
Minimal Operating Circuit
V_DD
V+
V_CC
UVP
ILIM1 OVP
ILIM2
ON1
ON2
BST1 BST2
DH1 DH2
LX1
LX2
DL1
DL2
TON
CS1
OUT1
PGOOD
REF
CS2
OUT2
SKIP
FB1
FB2
GND
BATTERY
4.5V TO 28V
MAX1845EEI
OUTPUT2
2.5V
________________________________________________________________ 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.