Rainbow Electronics MAX1774 - Manual

General Description
The MAX1774 is a complete power-supply solution for
PDAs and other hand-held devices. It integrates two
high-efficiency step-down converters, a boost converter
for backup battery regulation, and four voltage detec-
tors in a small 32-pin QFN or 28-pin QSOP package.
The MAX1774 accepts inputs from +2.7V to +28V and
provides an adjustable main output from 1.25V to 5.5V
at over 2A. The secondary core converter delivers an
adjustable voltage from 1V to 5V and can deliver up to
1.5A. Both the main and core regulators have separate
shutdown inputs.
When the AC adapter power is removed, an external P-
channel MOSFET switches input to the main battery.
When the main battery is low, the backup step-up con-
verter sustains the main output voltage. When the back-
up battery can no longer deliver the required load, the
system shuts down safely to prevent damage. Four on-
board voltage detectors monitor the status of the AC
adapter power, main battery, and backup battery.
The MAX1774 evaluation kit is available to help reduce
design time.
________________________Applications
Hand-Held Computers
PDAs
Internet Access Tablets
POS Terminals
Subnotebooks
Features
♦ Dual, High-Efficiency, Synchronous-Rectified
Step-Down Converters
♦ Thin, Small (1mm High) QFN Package
♦ Step-Up Converter for Backup Battery
♦ Main Power
Adjustable from +1.25V to +5.5V
Over 2A Load Current
Up to 95% Efficiency
♦ Core Power
Adjustable from 1V to 5V
Internal Switches
Up to 1.5A Load Current
Up to 91% Efficiency
♦ Automatic Main Battery Switchover
♦ 100% (max) Duty Cycle
♦ Up to 1.25MHz Switching Frequency
♦ Input Voltage Range from +2.7V to +28V
♦ Four Low-Voltage Detectors
♦ 170µA Quiescent Current
♦ 8µA Shutdown Current
♦ Digital Soft-Start
♦ Independent Shutdown Inputs
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
________________________________________________________________ Maxim Integrated Products 1
32 31 30 29 28 27 26
BKUP SHDNC SHDNM N.C. LXC INS LBO
25
N.C.
9 10 11 12 13 14 15
LXB
LXB2
BIN
BK
OFF ACI DBI LBI
16
REF
17
18
19
20
21
22
23
N.C.
GND
GND
GND
GND
FBM
CS+
CS-
FBC
GND
INC
8
7
6
5
4
3
2
CVH
PDRV
IN
CVL
NDRV
PGND
PGNDC
MAX1774
32 7mm x 7mm QFN
1 MDRV 24 ACO
TOP VIEW
Pin Configurations
19-1810; Rev 1; 1/02
EVALUATION KIT
AVAILABLE
Ordering Information
PART TEMP RANGE PIN-PACKAGE
MAX1774EEI -40°C to +85°C 28 QSOP
MAX1774EMJ -40°C to +85°C 32 7mm x 7mm QFN
AC
ADAPTER
MAIN
BATTERY
BACKUP
BATTERY
MAIN (+3.3V)
CORE (+1.8V)
AC OK
LOW MAIN BATTERY
DEAD MAIN BATTERY
MAX1774
Functional Diagram
Pin Configurations continued at end of data sheet.
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.