MAX1774EEI+ Fast Delivery |IC PHOENIX CO.,LIMITED

MAX1774EEI+ ,Dual, High-Efficiency, Step-Down Converter with Backup Battery SwitchoverApplications♦ Four Low-Voltage DetectorsHand-Held ComputersPDAs ♦ 170µA Quiescent CurrentInternet A ..
MAX1774EEI+ ,Dual, High-Efficiency, Step-Down Converter with Backup Battery SwitchoverFeaturesThe MAX1774 is a complete power-supply solution for♦ Dual, High-Efficiency, Synchronous-Rec ..
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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
FeaturesDual, 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% EfficiencyCore Power
Adjustable from 1V to 5V
Internal Switches
Up to 1.5A Load Current
Up to 91% EfficiencyAutomatic 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 Switchover313029282726
BKUPSHDNCSHDNMN.C.LXCINSLBO
N.C.1112131415
LXB
LXB2
BIN
OFF
ACIDBILBI
REF
N.C.
GND
GND
GND
GND
FBM
CS+
CS-
FBC
GND
INC
CVH
PDRV
CVL
NDRV
PGND
PGNDC
MAX1774
32 7mm x 7mm QFNMDRV24ACO
TOP VIEW
Pin Configurations
19-1810; Rev 2; 12/03
EVALUATION KIT
AVAILABLE
Ordering Information
PARTTEMP RANGEPIN-PACKAGE
MAX1774EEI-40°C to +85°C28 QSOP
MAX1774EGJ-40°C to +85°C32 7mm x 7mm QFN
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.
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 Range...........................-40°C to +85°C
Storage Temperature Range.............................-65°C to +150°C
Temperature (soldering, 10s)..........................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
Input VoltageVIN2.728V
Input Quiescent Supply CurrentIINVFBM = +1.5V, VFBC = +1.5V,
V SHDNM = V SHDNC = +3.3V1840µA
CS- Quiescent Supply CurrentICS-VFBM = +1.5V, VFBC = +1.5V,
V SHDNM = V SHDNC = +3.3V110220µA
Core Regulator Quiescent
Supply CurrentIINCVFBM = +1.5V, VFBC = +1.5V,
V SHDNM = V SHDNC = +3.3V60105µA
Backup Mode BIN Quiescent
Supply CurrentIBIN
VBIN = +3.3V, CS- open
VFBM = +1.5V, V SHDNM = +3.3V,
V BKOFF = +1.5V, SHDNC = GND105µA
IN Shutdown Supply CurrentSHDNM = SHDNC = GND840µA
MAIN REGULATOR
Main Output Voltage Adjust
Range1.255.5V
FBM Regulation ThresholdVFBMV(CS+ - CS-) = 0 to +60mV,
VIN = +3.5V to +28V1.211.251.29V
FBM Input CurrentIFBMVFBM = +1.3V-0.10.1µA
Current-Limit ThresholdVCS+ - VCS-6080100mV
Minimum Current-Limit
ThresholdVCS+ - VCS-51525mV
Valley Current ThresholdVCS+ - VCS-405060mV
Zero Current ThresholdVCS+ - VCS-0515mV
PDRV, NDRV Gate Drive
ResistanceVCS- = +3.3V, IPDRV, INDRV = 50mA25.5Ω
CS- to CVL Switch ResistanceICVL = 50mA4.59.5Ω
PDRV, NDRV Dead Time50ns
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
Maximum Duty Cycle100%
Minimum On-Time200400650ns
Minimum Off-Time200400650ns
CORE REGULATOR
Input Voltage RangeVINC2.65.5V
VINC rising2.402.472.55INC Undervoltage LockoutVINC falling2.302.372.45Vor e Outp ut V ol tag e Ad j ust Rang e1.05.0V
Maximum Core Load CurrentVCORE = 1.8V (Note 1)11.5A
FBC Regulation ThresholdVFBCVINC = +2.5 to +5.5V, I O U T C = 0 to 200mA0.971.01.03V
FBC Input CurrentIFBCVFBC = +1.3V-0.10.1µA
Dropout VoltageIOUTC = 400mA0.10.25V
LXC Leakage CurrentILXCVINC = +5.5V, V L X C = 0 to +5.5V-1010µA
LXC P-Channel, N-Channel On-
Resistance0.250.5Ω
LXC P-Channel Current LimitICLC120018003000mA
LX C P - C hannel M i ni m um C ur r ent100250400mA
LXC N-Channel Valley Current90014002400mA
LXC N-Channel Zero-Crossing
Current40110170mA
LXC Dead Time50ns
Max Duty Cycle100%
Minimum On-Time170400690ns
Minimum Off-Time170400690ns
BACKUP REGULATOR
Backup Battery Input VoltageVBBATT0.95.5V
LXB N-Channel On-ResistanceVCS- = +3.3V, ILXB = 50mA1.93.5Ω
LXB Current Limit200350600mA
LXB Leakage CurrentVLXB = +5.5V, VFBM = +1.3V1µA
BIN Leakage CurrentIBINVBIN = +5.5V, CS- = BKOFF =
SHDNC = SHDNM = GND1µA
BIN, CS- Switch ResistanceVCS- = +3.3V, BKOFF = GND,
SHDNM = CVL7.515Ω
BIN Switch Zero-Crossing
ThresholdBIN = + 2.5V , BKOFF = SHDNC =
SHDNM = C V L1735mV
LXB Maximum On-Time2.85.69.2µs
Zero Crossing Detector Timeout40µs
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
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
REFERENCE
Reference VoltageVREF1.231.251.27V
Reference Load RegulationIREF = 0 to 50µA10mV
Reference Line RegulationVCS- = +2.5V to +5.5V, IREF = 50µA5mV
Reference Sink Current10µA
CVL, CVH REGULATORS
ICVL = 50mA, VCS- = 02.62.83.1CVL Output VoltageVCVLICVL = 50mA, VCS- = +3.3V3.2V
CVL Switchover ThresholdCS- rising, hysteresis = 100mV typical2.402.472.55V
VIN = +4V, ICVH = 25mAVIN -
VIN -
CVH Output VoltageVCVH
VIN = +12V, ICVH = 50mAVIN -
VIN -
CVH Switchover ThresholdVINVIN rising, hysteresis = 350mV typ5.5V
VCVL rising2.402.472.55CVL Undervoltage LockoutVCVL falling2.302.372.45V
LOW-VOLTAGE COMPARATORS
V BKOFF rising0.510.550.59Backup Regulator Shutdown
ThresholdV BKOFF
V BKOFF falling0.460.500.54
BKOFF Input Bias CurrentV BKOFF = +5.5V1µA
LBI ThresholdVLBIVLBI falling, hysteresis = 50mV typical1.171.201.23V
DBI ThresholdVDBIVDBI falling, hysteresis = 50mV typical1.171.201.23V
BKUP Low-Input Threshold0.4V
LBI, DBI Input Leakage CurrentVLBI = VDBI = +1.3V100nA
LBO, BKUP, ACO, MDRV
Output LowISINK = 1mA0.4V
LBO, BKUP, ACO, MDRV
Output Leakage Current
VLBI = +1.3V, VACI = +12V, V ACO =
V LBO = V BKUP = +5.5V, V MDRV = +28V1.0µA
ACI ThresholdVACI – VINS, ACI falling0.220.35V
ACI Input Leakage CurrentVACI = +1.3V100nA
INS Input Leakage CurrentVINS = +3.3V1.510µA
LOGIC INPUTS
SHDNM, SHDNC Input Low
Voltage0.4V
SHDNM, SHDNC Input High
Voltage2.0V
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
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
SHDNM, SHDNC Input Low
CurrentSHDNM = SHDNC = GND-11µA
SHDNC Input High CurrentV SHDNC = +5.5V5µA
SHDNM Input High CurrentV SHDNM = +5V225µA
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)
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
Input VoltageVIN2.728V
Input Quiescent Supply CurrentIINVFBM = +1.5V, VFBC = +1.5V, V SHDNM =
V SHDNC = +3.3V40µA
CS- Quiescent Supply CurrentICS-VFBM = +1.5V, VFBC = +1.5V, V SHDNM =
V SHDNC = +3.3V220µA
Core Regulator Quiescent
Supply CurrentIINCVFBM = +1.5V, VFBC = +1.5V, V SHDNM =
V SHDNC = +3.3V105µA
Backup Mode BIN Quiescent
Supply CurrentIBIN
VBIN = +3.3V, CS- open
VFBM = +1.5V, V SHDNM = +3.3V,
V BKOFF = +1.5V, SHDNC = GND
110µA
IN Shutdown Supply CurrentSHDNM = SHDNC = GND40µA
MAIN REGULATOR
Main Output Voltage Adjust
Range1.255.5V
FBM Regulation ThresholdVFBMV(CS+ - CS-) = 0 to +60mV,
VIN = +3.5V to +28V1.211.29V
FBM Input CurrentIFBMVFBM = +1.3V-0.10.1µA
Current-Limit ThresholdVCS+ - VCS-60100mV
Minimum Current-Limit
ThresholdVCS+ - VCS-525mV
Valley Current ThresholdVCS+ - VCS-4060mV
Zero Current ThresholdVCS+ - VCS-015mV
PDRV, NDRV Gate Drive
ResistanceVCS- = +3.3V, IPDRV, INDRV = 50mA5.5Ω
CS- to CVL Switch ResistanceICVL = 50mA9.5Ω
Maximum Duty Cycle100%
Minimum On-Time200650ns
Minimum Off-Time200650ns
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
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
CORE REGULATOR
Input Voltage RangeVINC2.65.5V
VINC rising2.392.55INC Undervoltage LockoutVINC falling2.292.45V
Core Output Voltage Adjust
Range1.05.0V
Maximum Core Load CurrentVCORE = 1.8V (Note 1)1A
FBC Regulation ThresholdVFBCVINC = +2.5 to +5.5V,
IOUTC = 0 to 200mA0.971.03V
FBC Input CurrentIFBCVFBC = +1.3V-0.10.1µA
Dropout VoltageIOUTC = 400mA0.25V
LXC Leakage CurrentILXCVINC = +5.5V, VLXC = 0 to +5.5V-1010µA
LXC P-Channel, N-Channel
On-Resistance0.5Ω
LXC P-Channel Current Limit12003010mA
LXC P-Channel Minimum
Current100420mA
LXC N-Channel Valley Current8802450mA
LXC N-Channel Zero-Crossing
Current40170mA
Max Duty Cycle100%
Minimum On-Time160700ns
Minimum Off-Time170690ns
BACKUP REGULATOR
Backup Battery Input VoltageVBBATT0.95.5V
LXB N-Channel On ResistanceVCS- = +3.3V, ILXB = 50mA3.5Ω
LXB Current Limit200600mA
LXB Leakage CurrentVLXB = +5.5V, VFBM = +1.3V1µA
BIN Leakage CurrentIBINVBIN = +5.5V, CS- = BKOFF =
SHDNC = SHDNM = GND1µA
BIN, CS- Switch ResistanceVCS- = +3.3V, BKOFF = GND,
SHDNC = CVL15Ω
BIN Switch Zero-Crossing
Threshold
VBIN = +2.5V, BKOFF = SHDNC =
SHDNM = CVL35mV
LXB Maximum On-Time2.89.2µs
REFERENCE
Reference VoltageVREF1.2201.275V
Reference Load RegulationIREF = 0 to 50µA10mV
Reference Line RegulationVCS- = +2.5V to +5.5V, IREF = 50µA5mV
Reference Sink Current10µA
ELECTRICAL CHARACTERISTICS(continued)
(Figure 1, VIN= VINS = +12V, VINC= VCS+= VCS- = +3.3V, VCORE= +1.8V, TA= -40°C to +85°C,unless otherwise noted.) (Note 2)
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
PARAMETERSYMBOLCONDITIONSMINMAXUNITS
CVL, CVH REGULATORS
CVL Output VoltageVCVLICVL = 50mA, VCS- = 02.63.1V
CVL Switchover ThresholdVCS- rising, hysteresis = 100mV typical2.402.55V
VIN = +4V, ICVH = 25mAVIN - 2.8
CVH Output VoltageVCVH
VIN = +12V, ICVH = 50mAVIN - 3.65
VCVL rising2.402.57CVL Undervoltage LockoutVCVL falling2.302.47V
LOW-VOLTAGE COMPARATORS
V BKOFF rising0.510.59Backup Regulator Shutdown
ThresholdV BKOFF
V BKOFF falling0.460.54
BKOFF Input Bias CurrentV BKOFF = +5.5V1µA
LBI ThresholdVLBIVLBI falling, hysteresis = 50mV typical1.171.23V
DBI ThresholdVDBIVDBI falling, hysteresis = 50mV typical1.171.23V
BKUP Low-Input Threshold0.4V
LBI, DBI Input Leakage CurrentVLBI, VDBI = +28V100nA
LBO, BKUP, ACO, MDRV
Output LowISINK = 1mA0.4V
LBO, BKUP, ACO, MDRV
Output Leakage Current
VLBI = +1.3V, VACI = VIN = +12V, VACO =
V LBO = V BKUP = +5.5V, V MDRV = +28V1.0µA
ACI ThresholdVACI - VINS, ACI falling0.5V
ACI Input Leakage CurrentVACI = +1.3V100nA
MAIN Input Leakage CurrentVINS = +3.3V10µA
LOGIC INPUTS
SHDNM, SHDNC Input Low
Voltage0.4V
SHDNM, SHDNC Input High
Voltage2.0V
SHDNM, SHDNC Input Low
CurrentSHDNM = SHDNC = GND-11µA
SHDNC Input High CurrentV SHDNC = +5.5V5µA
SHDNM Input High CurrentV SHDNM = +28V25µA
ELECTRICAL CHARACTERISTICS(continued)
(Figure 1, VIN= VINS = +12V, VINC= VCS+= VCS- = +3.3V, VCORE= +1.8V, TA= -40°C to +85°C,unless otherwise noted.) (Note 2)
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.)
110100100010,000
MAIN EFFICIENCY vs. LOAD
MAX1774-01
LOAD (mA)
EFFICIENCY (%)40
VIN = +5V
VIN = +15V
VIN = +3.3V
VIN = +18V
VIN = +12V
VMAIN = 3.3V
CORE EFFICIENCY vs. LOAD
MAX1774-02
LOAD (mA)
EFFICIENCY (%)
VIN = +5V
VIN = +2.7V
VIN = +3.3V
VCORE = 1.8V
BACKUP EFFICIENCY vs. LOAD
MAX1774-03
LOAD (mA)
EFFICIENCY (%)40
VBBATT = +0.8V
VBBATT = +1.0VVBBATT = +2.5V
VMAIN = 3.3V
MAIN SWITCHING WAVEFORMS
(HEAVY LOAD 1A)
MAX1774-07
5µs/divLX5V/div
20mV
-20mV
500mA
1000mA
1500mA
VMAIN
(AC-COUPLED)
20mV/div
IL1
500mA/div
VREF ACCURACY vs. TEMPERATURE
MAX1774-04
REF
ACCURACY (%)
TEMPERATURE (°C)
REF
ACCURACY (%)
REFERENCE LOAD REGULATION
MAX1774-05
IREF (µA)
MAIN SWITCHING WAVEFORMS
(LIGHT LOAD 100mA)
MAX1774-06
5µs/divLX
5V/div
40mV
20mV
VMAIN
(AC-COUPLED)
20mV/div
ILI
500mA/div
-20mV
500mA
MAX1774
Dual, High-Efficiency, Step-Down
Converter with Backup Battery Switchover
CORE SWITCHING WAVEFORMS
(HEAVY LOAD 500mA)
MAX1774-09
2µs/div
20mV
-20mV
500mA
VCORE
(AC-COUPLED)
20mV/div
500mA/div
LXC2V/div
CORE LINE-TRANSIENT RESPONSE
MAX1774-11
VINC
2V/div
VCORE
(AC-COUPLED)
50mV/div
1µs/div
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN= +5V, VINC= +3.3V, TA= +25°C, unless otherwise noted.)
CORE SWITCHING WAVEFORMS
(LIGHT LOAD 50mA)
MAX1774-08
1µs/div
3.3VLX
2V/div
IL2
500mA/div
500mA
VCORE
(AC-COUPLED)
20mV/div
MAIN LOAD-TRANSIENT RESPONSE
MAX1774-121000mA
500mA
IMAIN
500mA/div
-20mV
VMAIN
(AC-COUPLED)
20mV/div
20mV
100µs/div
MAIN LOAD-TRANSIENT RESPONSE
50mA TO 500mA
MAX1774-13
500mA
VMAIN
(AC-COUPLED)
10mV/div
IMAIN
500mA/div
10mV
-10mV
100µs/div
MAIN LINE-TRANSIENT RESPONSE
MAX1774-10
12V
50mV
-50mV
10VVIN
5V/div
VMAIN
(AC-COUPLED)
50mV/div
100µs/div
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.)
TURN-ON RESPONSE
MAX1774-145VVOUT
1V/div2V
100µs/div
400µA
200µA
INPUT
CURRENT
200mA/div
VSHDN
5V/div
INPUT CURRENT
VMAINVCORE
BACKUP SWITCHOVER RESPONSE
MAX1774-15
VBKUP
5V/div
IBBATT
50mA/div
VBIN
10mV/div
VMAIN
10mV/div
5µs/div
Pin Description
PIN
QSOPQFNNAMEFUNCTION
130SHDNMShutdown for Main Regulator. Low voltage on SHDNM shuts off the main output. For normal
operation, connect SHDNM to IN.
231SHDNCShutdown for Core Regulator. Low voltage on SHDNC shuts off the core output. For normal
operation, connect SHDNC to CVL.
332BKUPOpen-Drain Backup Input/Output. The device is in backup mode when BKUP is low. BKUP can be
externally pulled low to place the device in backup mode.MDRV
Open-Drain Drive Output. MDRV goes low when the ACI voltage drops below the main voltage plus
220mV and device is not in backup. Connect MDRV to the gate of the main battery P-channel
MOSFET to switch the battery to IN when the AC adapter voltage is not present.PGNDCPower Ground for the Core Converter. Connect all grounds together close to the IC.PGNDPower Ground. Ground for NDRV and core output synchronous rectifier. Connect all grounds
together close to the IC.NDRVN-Channel Drive Output. Drives the main output synchronous-rectifier MOSFET. NDRV swings
between CVL and PGND.CVL
Low-Side Bypass. CVL is the output of an internal LDO regulator. This is the internal power supply
for the device control circuitry as well as the N-channel driver. Bypass CVL with a 1.0µF or greater
capacitor to GND. When CS- is above the CVL switchover threshold (2.47V), CVL is powered from
the main output.INPower Supply Input7PDRVP - C hannel D r i ve Outp ut. D r i ves the m ai n outp ut hi g h- si d e M OS FE T sw i tch. P D RV sw i ng s b etw een IN and V H . The vol tag e at C V H i s r eg ul ated at V IN - 4.2V unl ess the i np ut vol tag e i s l ess than 5.5V .8CVHHigh-Side Drive Bypass. This is the low-side of the P-channel driver output. Bypass with a 1.0µF
capacitor or greater to IN. When the input voltage is less than 5.5V, CVH is switched to PGND.9LXB
Backup Converter Switching Node. Connect an inductor from LXB to the backup battery and a
Schottky diode to BIN to complete the backup converter. In backup mode, this step-up converter
powers the main output from the backup battery through BIN.
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
QSOPQFNNAMEFUNCTION
—10LXB2Backup Converter Switching Node. Connect LXB2 to LXB as close to the IC as possible.11BINBackup Batter y Inp ut. C onnect BIN to the outp ut of the b ackup b oost r eg ul ator . Byp ass BIN w i th a 10µF or r eater cap aci tor to GN D . W hen the M AX 1774 i s i n b ackup m od e, BIN p ow er s the m ai n outp ut.12BKOFF
Backup D i sab l e Inp ut. D r i vi ng BKO FF b el ow + 0.5V d i sab l es the b ackup m od e. In b ackup m od e, theevi ce enter s shutd ow n w hen thi s p i n i s p ul l ed l ow . BKO FF can b e d r i ven fr om a d i g i tal si g nal or can b e
used as a l ow b atter y d etector to d i sab l e the b ackup conver ter w hen the b ackup b atter y i s l ow .13ACIAC Adapter Low-Voltage Detect Input. Connect to adapter DC input. When the voltage at ACI falls
below the voltage at INS plus +0.22V, ACO asserts.14DBID ead Batter y Inp ut. C onnect D BI to the m ai n b atter y thr oug h a r esi sti ve voltage-divider. W hen D BI d r op sel ow + 1.20V , no AC ad ap ter i s connected ( ACO i s l ow , b ut m ai n outp ut sti l l avai l ab l e) , BKU P asser ts.15LBILow-Battery Input. Connect LBI to the main battery through a r esi sti ve voltage-divider. When the
voltage at LBI drops below +1.20V, LBO asserts.16REFReference Voltage Output. Bypass REF to GND with a 0.22µF or greater capacitor.17, 25,N.C.No Connection. Not Internally Connected.18FBMMain Output Feedback. Connect FBM to a resistive voltage-divider to set main output voltage
between +1.25V to +5.5V.19CS+
Main Regulator High-Side Current-Sense Input. Connect the sense resistor between CS+ and CS-.
This voltage is used to set the current limit and to turn off the synchronous rectifier when the
inductor current approaches zero.20CS-Main Regulator Low-Side Current-Sense Input. Connect CS- to the main output.21FBCC or e Outp ut Feed b ack. C onnect FBC to a resistive voltage-divider to set cor e outp ut b etw een + 1.0V
to + 5.0V .22GNDAnalog Ground23INCCore Supply Input24ACOLow AC Output. Open drain ACO asserts when ACI falls below the main output voltage plus 0.22V.26LBOOpen-Drain Low-Battery Output. LBO asserts when LBI falls below +1.20V.27INSPower-Supply Input Voltage Sense Input. Connect INS to the power-supply input voltage.28LXCCore Converter Switching Node
Pin Description (continued)

Partno	Mfg	Dc	Qty	Available	Descript
MAX1774EEI+ \|MAX1774EEI	MAXIM	N/a	65	avai	Dual, High-Efficiency, Step-Down Converter with Backup Battery Switchover
MAX1774EEI+ \|MAX1774EEI	MAX	N/a	153	avai	Dual, High-Efficiency, Step-Down Converter with Backup Battery Switchover