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MAX1774EEIMAXIMN/a6698avaiDual, High-Efficiency, Step-Down Converter with Backup Battery Switchover
MAX1774EEIMAXN/a1960avaiDual, High-Efficiency, Step-Down Converter with Backup Battery Switchover
MAX1774EEIMAXIM ?N/a28avaiDual, High-Efficiency, Step-Down Converter with Backup Battery Switchover


MAX1774EEI ,Dual, High-Efficiency, Step-Down Converter with Backup Battery SwitchoverApplications

MAX1774EEI
Dual, High-Efficiency, Step-Down Converter with Backup Battery Switchover
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 PackageStep-Up Converter for Backup BatteryMain 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 Switchover100% (max) Duty CycleUp to 1.25MHz Switching FrequencyInput Voltage Range from +2.7V to +28VFour Low-Voltage Detectors170µA Quiescent Current8µA Shutdown CurrentDigital Soft-StartIndependent Shutdown Inputs
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
Pin Configurations
Ordering Information
Functional Diagram
Pin Configurations continued at end of data sheet.
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS

(Figure 1, VIN= VINS +12V, VINC= VCS-= VCS+= +3.3V, VCORE= +1.8V, TA= 0°C to +85°C,unless otherwise noted. Typical values are at= +25°C.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
IN, SHDNM, MDRV, DBI, LBI, ACI,
CVH to GND.......................................................-0.3V to +30V
IN to CVH, PDRV......................................................-0.3V to +6V
BIN to CS-.................................................................-0.3V to +6V
LXB to GND................................................-0.3V to (VBIN+ 0.7V)
PDRV to GND..................................(VCVH- 0.3V) to (VIN+ 0.3V)
All Other Pins to GND...............................................-0.3V to +6V
PGND to GND.......................................................-0.3V to +0.3V
Continuous Power Dissipation
28-Pin QSOP (derate 10.8mW/°C above +70°C)........860mW
32-Pin QFN (derate 23.2mW/°C above +70°C)........1860mW
Operating Temperature.......................................-40°C to +85°C
Storage Temperature.........................................-65°C to +150°C
Temperature (soldering, 10s)..........................................+300°C
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
ELECTRICAL CHARACTERISTICS (continued)

(Figure 1, VIN= VINS = +12V, VINC= VCS-= VCS+= +3.3V, VCORE= +1.8V, TA= 0°C to +85°C,unless otherwise noted. Typical values are
at TA= +25°C.)
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
ELECTRICAL CHARACTERISTICS(continued)

(Figure 1, VIN= VINS =+12V, VINC= VCS-= VCS+= +3.3V, VCORE= +1.8V, TA= 0°C to +85°C,unless otherwise noted. Typical values are
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
ELECTRICAL CHARACTERISTICS

(Figure 1, VIN= VINS = +12V, VINC = VCS-= VCS+= +3.3V, VCORE= +1.8V, TA= -40°C to +85°C,unless otherwise noted.) (Note 2)
ELECTRICAL CHARACTERISTICS(continued)

(Figure 1, VIN= VINS =+12V, VINC= VCS-= VCS+= +3.3V, VCORE= +1.8V, TA= 0°C to +85°C,unless otherwise noted. Typical values are
at TA=+25°C.)
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
ELECTRICAL CHARACTERISTICS(continued)
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
ELECTRICAL CHARACTERISTICS(continued)
Note 1:
This parameter is guaranteed based on the LXC P-channel current limit and the LXC N-channel valley current.
Note 2:
Specifications to -40°C are guaranteed by design and not production tested.
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
Typical Operating Characteristics

(Circuit of Figure 1, VIN= +5V, VINC= +3.3V, TA= +25°C, unless otherwise noted.)
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN= +5V, VINC= +3.3V, TA= +25°C, unless otherwise noted.)
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
Detailed Description

The MAX1774 dual step-down DC-DC converter is
designed to power PDA, palmtop, and subnotebook
computers. Normally, these devices require two sepa-
rate power supplies–one for the processor and another
higher voltage supply for the peripheral circuitry. The
MAX1774 provides an adjustable +1.25V to +5.5V main
output designed to power the peripheral circuitry of
PDAs and similar devices. The main output delivers up
to 2A output current. The lower voltage core converter
has an adjustable +1.0V to +5.0V output, providing up
to 1.5A output current. Both regulators utilize a propri-
etary regulation scheme allowing PWM operation at
medium to heavy loads, and automatically switch to
pulse skipping at light loads for improved efficiency.
Under low-battery conditions, the MAX1774 enters
backup mode, making use of a low-voltage backup
battery and a step-up regulator to power the output.
Figure 1 is the MAX1774 typical application circuit.
Operating Modes for the
Step-Down Converters

When delivering low output currents, the MAX1774 oper-
ates in discontinuous conduction mode. Current through
the inductor starts at zero, rises as high as the minimum
current limit (IMIN), then ramps down to zero during
Pin Description (continued)
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