Rainbow Electronics MAX1844 - Manual

General Description
The MAX1844 pulse-width modulation (PWM) controller
provides high efficiency, excellent transient response,
and high DC output accuracy needed for stepping
down high-voltage batteries to generate low-voltage
CPU core or chipset/RAM supplies in notebook com-
puters.
Maxim’s proprietary Quick-PWM™ quick-response,
constant-on-time PWM control scheme handles wide
input/output voltage ratios with ease and provides
100ns “instant-on” response to load transients while
maintaining a relatively constant switching frequency.
Efficiency is enhanced by an ability to drive very large
synchronous-rectifier MOSFETs. Accurate current sens-
ing to ensure reliable overload protection is available
using an external current-sense resistor in series with
the synchronous rectifier. Alternatively, the synchronous
rectifier itself can be used for less accurate current
sensing at the lowest possible power dissipation.
Single-stage buck conversion allows the MAX1844 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
battery) at a higher switching frequency allows the mini-
mum possible physical size.
The MAX1844 is intended for CPU core, chipset,
DRAM, or other low-voltage supplies as low as 1V. It is
available in 20-pin QSOP, and QFN packages and
includes both adjustable overvoltage and undervoltage
protection.
For a dual step-down PWM controller with accurate cur-
rent limit, refer to the MAX1845. The MAX1714/ MAX1715
single/dual PWM controllers are similar to the MAX1844/
MAX1845 but do not use current-sense resistors.
Applications
Notebook Computers
CPU Core Supplies
Chipset/RAM Supplies as Low as 1V
1.8V and 2.5V Supplies
Features
♦ Ultra-High Efficiency
♦ Accurate Current-Limit Option
♦ Quick-PWM with 100ns Load-Step Response
♦ 1% V OUT Accuracy Over Line and Load
♦ 1.8V/2.5V Fixed or 1V to 5.5V Adjustable Output
Range
♦ 2V to 28V Battery Input Range
♦ 200/300/450/600kHz Switching Frequency
♦ Adjustable Overvoltage Protection
♦ Adjustable Undervoltage Protection
♦ 1.7ms Digital Soft-Start
♦ Drives Large Synchronous-Rectifier FETs
♦ 2V ±1% Reference Output
♦ Power-Good Window Comparator
MAX1844
High-Speed Step-Down Controller with
Accurate Current Limit for Notebook Computers
________________________________________________________________ Maxim Integrated Products 1
19-1993; Rev 1; 3/02
EVALUATION KIT
AVAILABLE
Pin Configuration appears at end of data sheet.
Quick-PWM is a trademark of Maxim Integrated Products.
V CC
5V INPUT
BATTERY
4.5V TO 28V
OUTPUT
2.5V
SHDN
ILIM
DL
LX
V+
BST
DH
CS
OUT
SKIP
V DD
MAX1844
UVP
REF
PGOOD
LATCH
OVP
FB
GND
Minimal Operating Circuit
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.
Ordering Information
PART TEMP RANGE PIN-PACKAGE
MAX1844EEP -40°C to +85°C 20 QSOP
MAX1844EGP -40°C to +85°C 20 QFN