General Description
The MAX17505/MAX17505S high-efficiency, high-
voltage, synchro nously rectified step-down converter with
dual integrated MOSFETs operates over a 4.5V to 60V
input. It delivers up to 1.7A and 0.9V to 90%VIN output
voltage. Built-in compensation across the output voltage
range eliminates the need for external components. The
feedback (FB) regulation accuracy over -40NC to +125NC
is ±1.1%. The device is available in a compact (4mm x
4mm) TQFN lead(Pb)-free package with an exposed pad.
Simulation models are available.
The device features a peak-current-mode control
architecture with a MODE feature that can be used to
operate the device in pulse-width modulation (PWM),
pulse-frequency modulation (PFM), or discontinuous-
conduction mode (DCM) control schemes. PWM operation
provides constant frequency operation at all loads, and is
useful in applications sensitive to switching frequency.
PFM operation disables negative inductor current and
additionally skips pulses at light loads for high efficiency.
DCM features constant frequency operation down to
lighter loads than PFM mode, by not skipping pulses but
only disabling negative inductor current at light loads.
DCM operation offers efficiency performance that lies
between PWM and PFM modes. The MAX17505S offers
a lower minimum on-time that allows for higher switching
frequencies and a smaller solution size.
A programmable soft-start feature allows users to reduce
input inrush current. The device also incorporates an
output enable/undervoltage lockout pin (EN/UVLO) that
allows the user to turn on the part at the desired input-
voltage level. An open-drain RESET pin provides a
delayed power-good signal to the sys tem upon achieving
successful regulation of the output voltage.
Applications
● IndustrialPowerSupplies
● DistributedSupplyRegulation
● BaseStationPowerSupplies
● WallTransformerRegulation
● High-VoltageSingle-BoardSystems
● General-PurposePoint-of-Load
Benets and Features
●EliminatesExternalComponentsandReducesTotal
Cost
• NoSchottky-SynchronousOperationforHigh
EfciencyandReducedCost
• Internal Compensation for Stable Operation at Any
Output Voltage
• All-Ceramic Capacitor Solution: Ultra-Compact
Layout with as Few as Eight External Components
● ReducesNumberofDC-DCRegulatorstoStock
• Wide4.5Vto60VInputVoltageRange
• 0.9V to 90%VIN Output Voltage
• Delivers Up to 1.7A Over Temperature
• 100kHzto2.2MHzAdjustableFrequencywith
External Synchronization
• MAX17505SAllowsHigherFrequencyOfOperation
• Available in a 20-Pin, 4mm x 4mm TQFN Package
● ReducesPowerDissipation
• PeakEfciency>90%
• PFMandDCMModesforHighLight-LoadEfciency
• Shutdown Current = 2.8FA (typ)
● OperatesReliably
• Hiccup-ModeCurrentLimitandAutoretryStartup
• Built-In Output-Voltage Monitoring (Open-Drain
RESET Pin)
• Resistor-ProgrammableEN/UVLOThreshold
• AdjustableSoft-StartandPrebiasedPower-Up
• HighIndustrial-40°Cto+125°CAmbientOperating
TemperatureRange/-40°Cto+150°CJunction
TemperatureRange
19-6907; Rev 2; 5/17
Ordering Information appears at end of data sheet.
MAX17505 4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
EVALUATION KIT AVAILABLE
VINtoPGND .........................................................-0.3V to +65V
EN/UVLOtoSGND ...............................................-0.3V to +65V
LXtoPGND................................................-0.3V to (VIN + 0.3V)
BSTtoPGND ........................................................-0.3V to +70V
BST to LX .............................................................-0.3V to +6.5V
BST to VCC ...........................................................-0.3V to +65V
FB, CF, RESET, SS, MODE, SYNC,
RTtoSGND .....................................................-0.3V to +6.5V
VCCtoSGND .......................................................-0.3V to +6.5V
SGNDtoPGND ....................................................-0.3V to +0.3V
LXTotalRMSCurrent ...........................................................±4A
Output Short-Circuit Duration .................................... Continuous
Continuous Power Dissipation (TA = +70ºC) (multilayer board)
TQFN (derate 30.3mW/ºC above TA = +70ºC) ......2424.2mW
JunctionTemperature ...................................................... +150ºC
StorageTemperatureRange .............................-65NC to +160ºC
Lead Temperature (soldering, 10s) ................................. +300ºC
Soldering Temperature (reflow) ....................................... +260ºC
(VIN = VEN/UVLO=24V,RRT = 40.2kI(500kHz),CVCC=2.2μF,VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET =
open, VBST to VLX = 5V, VFB = 1V, TA =-40°Cto+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.Allvoltagesare
referencedtoSGND,unlessotherwisenoted.)(Note2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
INPUT SUPPLY (VIN)
InputVoltageRange VIN 4.5 60 V
Input Shutdown Current IIN-SH VEN/UVLO = 0V (shutdown mode) 2.8 4.5
µA
Input Quiescent Current
IQ_PFM
VFB=1V,MODE=RT=open 118
VFB = 1V, MODE = open 162
IQ-DCM DCM mode, VLX = 0.1V 1.16 1.8
mA
IQ_PWM
Normal switching mode, fSW =500kHz,VFB
= 0.8V 9.5
Absolute Maximum Ratings (Note 1)
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.
Note 1: Junctiontemperaturegreaterthan+125°Cdegradesoperatinglifetimes.
PackagethermalresistanceswereobtainedusingthemethoddescribedinJEDECspecificationJESD51-7,usingafour-layerboard.
For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial.
Electrical Characteristics
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”,
“#”,or“-”inthepackagecodeindicatesRoHSstatusonly.Packagedrawingsmayshowadifferentsuffixcharacter,butthedrawing
pertainstothepackageregardlessofRoHSstatus.
PACKAGE TYPE: 20 TQFN
Package Code T2044+4
Outline Number 21-0139
Land Pattern Number 90-0409
THERMAL RESISTANCE, FOUR-LAYER BOARD
JunctiontoAmbient(θJA)33°C/W
JunctiontoCase(θJC) 2°C/W
Maxim Integrated
│
2
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
(VIN = VEN/UVLO=24V,RRT = 40.2kI(500kHz),CVCC=2.2μF,VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET =
open, VBST to VLX = 5V, VFB = 1V, TA =-40°Cto+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.Allvoltagesare
referencedtoSGND,unlessotherwisenoted.)(Note2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
ENABLE/UVLO (EN/UVLO)
EN/UVLO Threshold VENR VEN/UVLO rising 1.19 1.215 1.24 V
VENF VEN/UVLO falling 1.068 1.09 1.111
EN/UVLO Input Leakage Current IEN VEN/UVLO = 0V, TA = +25ºC -50 0 +50 nA
LDO
VCCOutputVoltageRange VCC
6V < VIN < 60V, IVCC = 1mA 4.75 5 5.25 V
1mA≤IVCC≤25mA
VCC Current Limit IVCC-MAX VCC = 4.3V, VIN = 6V 26.5 54 100 mA
VCC Dropout VCC-DO VIN = 4.5V, IVCC = 20mA 4.2 V
VCC UVLO VCC_UVR VCC rising 4.05 4.2 4.3 V
VCC_UVF VCC falling 3.65 3.8 3.9
POWER MOSFET AND BST DRIVER
High-SidenMOSOn-Resistance RDS-ONH ILX = 0.3A 165 325 mI
Low-SidenMOSOn-Resistance RDS-ONL ILX = 0.3A 80 150 mI
LX Leakage Current ILX_LKG VLX = VIN - 1V, VLX = VPGND + 1V, TA = +25ºC -2 +2 µA
SOFT-START (SS)
Charging Current ISS VSS = 0.5V 4.7 5 5.3 µA
FEEDBACK (FB)
FBRegulationVoltage VFB_REG MODE=SGNDonVCC 0.89 0.9 0.91 V
MODE = OPEN 0.89 0.915 0.936
FB Input Bias Current IFB 0 < VFB < 1V, TA = +25ºC -50 +50 nA
MODE
MODE Threshold
VM-DCM MODE = VCC (DCM mode) VCC -
1.6
V
VM-PFM MODE = open (PFM mode) VCC / 2
VM-PWM MODE=GND(PWMmode) 1.4
CURRENT LIMIT
Peak Current-Limit Threshold IPEAK-LIMIT 2.4 2.8 3.25 A
RunawayCurrent-LimitThreshold IRUNAWAY-LIMIT 2.9 3.4 3.9 A
Valley Current-Limit Threshold ISINK-LIMIT
MODE = open/VCC -0.16 0 +0.16 A
MODE=GND -1.8
PFM Current-Limit Threshold IPFM MODE = open 0.6 0.75 0.9 A
Electrical Characteristics (continued)
Maxim Integrated
│
3
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
(VIN = VEN/UVLO=24V,RRT = 40.2kI(500kHz),CVCC=2.2μF,VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET =
open, VBST to VLX = 5V, VFB = 1V, TA =-40°Cto+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.Allvoltagesare
referencedtoSGND,unlessotherwisenoted.)(Note2)
Note 2: Alllimitsare100%testedat+25°C.Limitsovertemperatureareguaranteedbydesign.
Note 3: See the Overcurrent Protection/Hiccup Mode section for more details.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
RT AND SYNC
Switching Frequency fSW
RRT = 210kΩ 90 100 110
kHz
RRT = 102kΩ 180 200 220
RRT = 40.2kΩ 475 500 525
RRT = 8.06kΩ 1950 2200 2450
RRT = open 460 500 540
SYNCFrequencyCaptureRange fSWsetbyRRT 1.1 x
fSW
1.4 x
fSW kHz
SYNC Pulse Width 50 ns
SYNC Threshold VIH 2.1 V
VIL 0.8
FB Undervoltage Trip Level to
CauseHiccup VFB-HICF 0.56 0.58 0.6 V
HiccupTimeout (Note 3) 32,768 Cycles
Minimum On-Time tON-MIN
MAX17505 135 ns
MAX17505S 55 80 ns
Minimum Off-Time tOFF-MIN 140 160 ns
LX Dead Time 5 ns
RESET
RESET Output Level Low IRESET = 10mA 0.4 V
RESET Output Leakage Current TA = TJ = +25ºC, VRESET = 5.5V -0.1 +0.1 µA
FB Threshold for RESET Assertion VFB-OKF VFB falling 90.5 92 94 %VFB-
REG
FB Threshold for RESET
Deassertion VFB-OKR VFB rising 93.8 95 97.2 %VFB-
REG
RESET Deassertion Delay After FB
Reaches95%Regulation 1024 Cycles
THERMAL SHUTDOWN
Thermal-Shutdown Threshold Temperature rising 165 ºC
Thermal-ShutdownHysteresis 10 ºC
Electrical Characteristics (continued)
Maxim Integrated
│
4
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS=5600pF,RT=MODE=open,TA=-40°Cto
+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.AllvoltagesarereferencedtoGND,unlessotherwisenoted.)
30
40
50
60
70
80
90
100
0500 1000 1500
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505S 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PWM MODE, FIGURE 5CIRCUIT)
V
IN
= 48V
V
IN
= 36V
V
IN
= 12V
MODE = SGND
V
IN
= 24V
toc01a
1700
0
10
20
30
40
50
60
70
80
90
100
0500 1000 1500
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505 3.3V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PWM MODE, FIGURE 4 CIRCUIT)
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = SGND
toc02
1700
40
50
60
70
80
90
100
0500 1000 1500
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PWM MODE, FIGURE 3 CIRCUIT)
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = SGND
toc01
1700
20
30
40
50
60
70
80
90
100
0500 1000 1500
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505S 3.3V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PWM MODE, FIGURE 6 CIRCUIT)
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = SGND
V
IN
= 48V
toc02a
1700
30
40
50
60
70
80
90
100
10 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505S 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PFM MODE, FIGURE 5CIRCUIT)
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = OPEN
1700
toc03a
30
40
50
60
70
80
90
100
110 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = OPEN
1700
toc03
MAX17505 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PfM MODE, FIGURE 3 CIRCUIT)
0
10
20
30
40
50
60
70
80
90
100
110 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505 3.3V OUTPUT
EFFICIENCY VS. LOAD CURRENT
(PFM MODE, FIGURE 4 CIRCUIT)
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = OPEN
toc04
Typical Operating Characteristics
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
5
www.maximintegrated.com
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS=5600pF,RT=MODE=open,TA=-40°Cto
+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.AllvoltagesarereferencedtoGND,unlessotherwisenoted.)
30
40
50
60
70
80
90
100
110 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(DCM MODE, FIGURE 3 CIRCUIT)
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = V
CC
1700
toc05
10
20
30
40
50
60
70
80
90
100
110 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505S 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(DCM MODE, FIGURE 5CIRCUIT)
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = V
CC
toc05a
30
40
50
60
70
80
90
100
10 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505S 3.3V OUTPUT
EFFICIENCY VS. LOAD CURRENT
(PFM MODE, FIGURE 6CIRCUIT)
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
MODE = OPEN
1700
toc04a
0
10
20
30
40
50
60
70
80
90
100
110 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505 3.3V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(DCM MODE, FIGURE 4 CIRCUIT)
VIN = 48V
VIN = 36V
VIN = 24V
VIN = 12V
MODE = VCC
1700
toc06
4.95
4.96
4.97
4.98
4.99
5.00
5.01
5.02
5.03
5.04
5.05
0500 1000 1500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17505 5V OUTPUT
LOAD AND LINE REGULATION
(PWM MODE, FIGURE 3 CIRCUIT)
V
IN
= 48V
V
IN
= 36V
V
IN
= 24V
V
IN
= 12V
toc07
MODE = SGND
1700
20
30
40
50
60
70
80
90
100
110 100 1000
EFFICIENCY (%)
LOAD CURRENT (mA)
MAX17505S 3.3V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(DCM MODE, FIGURE 6CIRCUIT)
VIN = 48V
VIN = 36V
VIN = 24V
VIN = 12V
MODE = VCC
1700
toc06a
4.92
4.93
4.94
4.95
4.96
4.97
4.98
4.99
5.00
5.01
5.02
0500 1000 1500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17505S 5V OUTPUT
LOAD AND LINE REGULATION
(PWM MODE, FIGURE 5CIRCUIT)
V
IN
= 36V
V
IN
= 48V
V
IN
= 24V
V
IN
= 12V
MODE = SGND
toc07a
1700
Typical Operating Characteristics (continued)
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
6
www.maximintegrated.com
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS=5600pF,RT=MODE=open,TA=-40°Cto
+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.AllvoltagesarereferencedtoGND,unlessotherwisenoted.)
3.10
3.15
3.20
3.25
3.30
3.35
3.40
3.45
3.50
0500 1000 1500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17505S 3.3V OUTPUT
LOAD AND LINE REGULATION
(PWM MODE, FIGURE 6CIRCUIT)
VIN = 36V
VIN = 48V
VIN = 24V
VIN = 12V
MODE = SGND
toc08a
1700
4.5
4.6
4.7
4.8
4.9
5.0
5.1
5.2
5.3
5.4
5.5
0500 1000 1500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17505 5V OUTPUT
LOAD AND LINE REGULATION
(PFM MODE, FIGURE 3 CIRCUIT)
V
IN
= 36V
V
IN
= 48V
V
IN
= 24V
V
IN
= 12V
toc09
MODE = OPEN
1700
3.26
3.27
3.28
3.29
3.30
3.31
3.32
3.33
3.34
3.35
3.36
0500 1000 1500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17505 3.3V OUTPUT
LOAD AND LINE REGULATION
(PWM MODE, FIGURE 4 CIRCUIT)
V
IN
= 36V
V
IN
= 48V
V
IN
= 24V
V
IN
= 12V
toc08
MODE = SGND
1700
4.75
4.80
4.85
4.90
4.95
5.00
5.05
5.10
5.15
5.20
5.25
0500 1000 1500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17505S 5V OUTPUT
LOAD AND LINE REGULATION
(PFM MODE, FIGURE 5CIRCUIT)
V
IN
= 36V
V
IN
= 48V
V
IN
= 12V
V
IN
= 24V
MODE = OPEN
toc09a
1700
3.00
3.10
3.20
3.30
3.40
3.50
3.60
0500 1000 1500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17505S 3.3V OUTPUT
LOAD AND LINE REGULATION
(PFM MODE, FIGURE 6CIRCUIT)
V
IN
= 36V
V
IN
= 48V
V
IN
= 12V
V
IN
= 24V
MODE = OPEN
toc10a
1700
3.27
3.28
3.29
3.30
3.31
3.32
3.33
3.34
3.35
3.36
3.37
0500 1000 1500
OUTPUT VOLTAGE (V)
LOAD CURRENT (mA)
MAX17505 3.3V OUTPUT
LOAD AND LINE REGULATION
(PFM MODE, FIGURE 4 CIRCUIT)
V
IN
= 36V
V
IN
= 48V
V
IN
= 12V
V
IN
= 24V
toc10
MODE = OPEN
1700
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
020 40 60 80 100
SWITCHING FREQUENCY (kHz)
R
RT
(kΩ)
SWITCHING FREQUENCY
vs. RT RESISTANCE
toc11
Typical Operating Characteristics (continued)
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
7
www.maximintegrated.com
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS=5600pF,RT=MODE=open,TA=-40°Cto
+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.AllvoltagesarereferencedtoGND,unlessotherwisenoted.)
1A/div
1ms/div
V
EN/UVLO
2V/div
MAX17505 5V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(1.7A LOAD CURRENT, FIGURE 3 CIRCUIT)
toc12
V
OUT
2V/div
V
RESET
5V/div
I
OUT
MODE = SGND
1A/div
1ms/div
V
EN/UVLO
5V/div
MAX17505S 5V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(1.7A LOAD CURRENT, FIGURE 5CIRCUIT)
V
OUT
I
OUT
2V/div
5V/div
V
RESET
toc12a
MODE = SGND
1A/div
1ms/div
V
EN/UVLO
2V/div
MAX17505 3.3V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(1.7A LOAD CURRENT, FIGURE 4 CIRCUIT)
toc13
V
OUT
2V/div
5V/div
V
RESET
I
OUT
MODE = SGND
2mS/div
V
EN/UVLO
2V/div
MAX17505 5V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(PFM MODE, 5mA LOAD CURRENT, FIGURE 3 CIRCUIT)
toc14
V
OUT
1V/div
5V/div
V
RESET
MODE = OPEN
1A/div
1mS/div
VEN/UVLO 5V/div
MAX17505S 3.3V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(1.7A LOAD CURRENT, FIGURE 6CIRCUIT)
VOUT
IOUT
2V/div
5V/div
VRESET
toc13a
MODE = SGND
2mS/div
V
EN/UVLO
5V/div
MAX17505S 5V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(PFM MODE, 5MA LOAD CURRENT, FIGURE 5CIRCUIT)
V
OUT
1V/div
5V/div
V
RESET
toc14a
MODE = OPEN
Typical Operating Characteristics (continued)
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
8
www.maximintegrated.com
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS=5600pF,RT=MODE=open,TA=-40°Cto
+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.AllvoltagesarereferencedtoGND,unlessotherwisenoted.)
2mS/div
VEN/UVLO 5/div
MAX17505S 3.3V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(PFM MODE, 5mA LOAD CURRENT, FIGURE 6CIRCUIT)
VOUT
1V/div
5V/div
toc15a
VRESET
MODE = OPEN
2ms/div
VEN/UVLO 2V/div
MAX17505 3.3V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(PFM MODE, 5mA LOAD CURRENT, FIGURE 4 CIRCUIT)
toc15
VOUT
1V/div
5V/div
VRESET
MODE = OPEN
1mS/div
V
EN/UVLO
5V/div
MAX17505S 5V OUTPUT
SOFT-START WITH 2.5V PREBIAS
(PWM MODE, FIGURE 5CIRCUIT)
V
OUT
2V/div
5V/div
V
RESET
toc16a
MODE = SGND
1mS/div
V
EN/UVLO
5V/div
MAX17505S 3.3V OUTPUT
SOFT-START WITH 2.5V PREBIAS
(PWM MODE, FIGURE 6CIRCUIT)
V
OUT
1V/div
5V/div
V
RESET
toc17a
MODE = OPEN
1ms/div
V
EN/UVLO
2V/div
MAX17505 3.3V OUTPUT
SOFT-START WITH 2.5V PREBIAS
(PFM MODE, FIGURE 4 CIRCUIT)
toc17
V
OUT
1V/div
5V/div
V
RESET
MODE = OPEN
1mS/div
V
EN/UVLO
2V/div
MAX17505 5V OUTPUT
SOFT-START WITH 2.5V PREBIAS
(PWM MODE, FIGURE 3 CIRCUIT)
toc16
V
OUT
2V/div
5V/div
V
RESET
MODE = SGND
Typical Operating Characteristics (continued)
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
9
www.maximintegrated.com
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS=5600pF,RT=MODE=open,TA=-40°Cto
+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.AllvoltagesarereferencedtoGND,unlessotherwisenoted.)
400nS/div
VLX
50mV/div
MAX17505S 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(1.7A LOAD CURRENT, FIGURE 5CIRCUIT)
VOUT (AC)
10V/div
1A/div
ILX
toc18a
MODE = SGND
1μs/div
VOUT (AC) 20mV/div
MAX17505 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(PWM MODE, NO LOAD, FIGURE 3 CIRCUIT)
toc19
VLX 10V/div
ILX 1A/div
MODE = SGND
1μs/div
V
OUT
(AC) 20mV/div
MAX17505 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(1.7A LOAD CURRENT, FIGURE 3 CIRCUIT)
toc18
V
LX
10V/div
I
LX
1A/div
MODE = SGND
400ns/div
50mV/div
MAX17505S 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(NO LOAD CURRENT, FIGURE 5CIRCUIT)
VOUT (AC)
10V/div
500mA/div
VLX
ILX
toc19a
MODE = SGND
4μs/div
100mV/div
MAX17505S 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(PFM MODE, 25mA LOAD CURRENT, FIGURE 5CIRCUIT)
V
OUT
(AC)
10V/div
500mA/div
toc20a
V
LX
I
LX
MODE = OPEN
10μs/div
VOUT (AC) 100mV/div
MAX17505 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(PFM MODE, 25mA LOAD, FIGURE 3 CIRCUIT)
toc20
10V/div
500mA/div
VLX
ILX
MODE = OPEN
1μs/div
VOUT (AC) 20mV/div
MAX17505 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(DCM MODE, 25mA LOAD, FIGURE 3 CIRCUIT)
toc21
VLX 10V/div
ILX 200mA/div
MODE = VCC
Typical Operating Characteristics (continued)
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
10
www.maximintegrated.com
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS=5600pF,RT=MODE=open,TA=-40°Cto
+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.AllvoltagesarereferencedtoGND,unlessotherwisenoted.)
1A/div
40μs/div
VOUT (AC) 100mV/div
MAX17505 5V OUTPUT
LOAD CURRENT STEPPED FROM 0.85ATO 1.7A
(PWM MODE, FIGURE 3 CIRCUIT)
toc22
IOUT
MODE = SGND
40μS/div
100mV/div
MAX17505S 5V OUTPUT
LOAD CURRENT STEPPED FROM 0.85A TO 1A
(PWM MODE, FIGURE 5 CIRCUIT)
V
OUT
(AC)
1A/div
I
LX
toc22a
MODE = SGND
1μs/div
VLX
20mV/div
MAX17505S 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(DCM MODE, 25mA LOAD CURRENT, FIGURE 5CIRCUIT)
VOUT (AC)
10V/div
200mA/div
ILX
toc21a
MODE = VCC
1A/div
100μs/div
V
OUT
(AC) 50mV/div
MAX17505 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 0.85ATO 1.7A
(PWM MODE, FIGURE 4 CIRCUIT)
toc23
I
OUT
MODE = SGND
500mA/div
40μs/div
VOUT (AC) 100mV/div
MAX17505 5V OUTPUT
LOAD CURRENT STEPPED FROM NO LOAD TO 0.85A
(PWM MODE, FIGURE 3 CIRCUIT)
toc24
IOUT
MODE = SGND
40μS/div
50mV/div
MAX17505S 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 0.85A TO 1.7A
(PWM MODE, FIGURE 6 CIRCUIT)
V
OUT
(AC)
1A/div
I
LX
toc23a
MODE = SGND
40μS/div
100mV/div
MAX17505S 5V OUTPUT
LOAD CURRENT STEPPED FROM NO LOAD TO 0.85A
(PWM MODE, FIGURE 5CIRCUIT)
V
OUT
(AC)
500mA/div
I
LX
toc24a
MODE = SGND
Typical Operating Characteristics (continued)
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
11
www.maximintegrated.com
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS=5600pF,RT=MODE=open,TA=-40°Cto
+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.AllvoltagesarereferencedtoGND,unlessotherwisenoted.)
500mA/div
2ms/div
V
OUT
(AC)
100mV/div
MAX17505 5V OUTPUT
LOAD CURRENT STEPPED FROM 5mA TO 0.85A
(PFM MODE, FIGURE 3 CIRCUIT)
toc26
I
OUT
MODE = OPEN
500mA/div
2ms/div
V
OUT
(AC) 100mV/div
MAX17505 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 5mA TO 0.85A
(PFM MODE, FIGURE 4 CIRCUIT)
toc27
I
OUT
MODE = OPEN
1mS/div
100mV/div
MAX17505S 5V OUTPUT
LOAD CURRENT STEPPED FROM 5MA TO 0.85A
(PFM MODE, FIGURE 5CIRCUIT)
VOUT (AC)
500mA/div
ILX
MODE = OPEN
toc26a
2mS/div
50mV/div
MAX17505S 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 5mA TO 0.85A
(PFM MODE, FIGURE 6CIRCUIT)
V
OUT
(AC)
500mA/div
I
LX
toc27a
MODE = OPEN
500mA/div
100μs/div
V
OUT
(AC) 50mV/div
MAX17505 3.3V OUTPUT
LOAD CURRENT STEPPED FROM NO LOAD TO 0.85A
(PWM MODE, FIGURE 4 CIRCUIT)
toc25
I
OUT
MODE = SGND
40μS/div
50mV/div
MAX17505S 3.3V OUTPUT
LOAD CURRENT STEPPED FROM NO LOAD TO 0.85A
(PWM MODE, FIGURE 6CIRCUIT)
V
OUT
(AC)
500mA/div
I
LX
toc25a
MODE = SGND
Typical Operating Characteristics (continued)
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
12
www.maximintegrated.com
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS=5600pF,RT=MODE=open,TA=-40°Cto
+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.AllvoltagesarereferencedtoGND,unlessotherwisenoted.)
500mA/div
200μs/div
V
OUT
(AC) 100mV/div
MAX17505 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 50mA TO 0.85A
(DCM MODE, FIGURE 4 CIRCUIT)
toc29
I
OUT
MODE = V
CC
500mA/div
200μs/div
V
OUT
(AC) 100mV/div
MAX17505 5V OUTPUT
LOAD CURRENT STEPPED FROM 50mA TO 0.85A
(DCM MODE, FIGURE 3 CIRCUIT)
toc28
I
OUT
MODE = V
CC
1A/div
20ms/div
V
OUT
2V/div
MAX17505 5V OUTPUT
OVERLOAD PROTECTION
(FIGURE 3 CIRCUIT)
toc30
I
OUT
MODE = V
CC
500mA/div
200μs/div
V
OUT
(AC) 100mV/div
MAX17505S 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 50mA TO 0.85A
(DCM MODE, FIGURE 6CIRCUIT)
I
OUT
MODE = V
CC
toc29a
500mA/div
200μs/div
V
OUT
(AC) 100mV/div
MAX17505S 5V OUTPUT
LOAD CURRENT STEPPED FROM 50mA TO 0.85A
(DCM MODE, FIGURE 5CIRCUIT)
I
OUT
MODE = V
CC
toc28a
1A/div
10ms/div
V
OUT
200mV/div
MAX17505S 5V OUTPUT
OVERLOAD PROTECTION
(FIGURE 5CIRCUIT)
I
OUT
MODE = V
CC
toc30a
Typical Operating Characteristics (continued)
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Maxim Integrated
│
13
www.maximintegrated.com
(VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2µF, CBST = 0.1µF, CSS=5600pF,RT=MODE=open,TA=-40°Cto
+125°C,unlessotherwisenoted.TypicalvaluesareatTA=+25°C.AllvoltagesarereferencedtoGND,unlessotherwisenoted.)
GAIN (dB)
FREQUENCY (Hz)
toc32
MAX17505 5V OUTPUT
BODE PLOT
(1.7A LOAD CURRENT, FIGURE 3 CIRCUIT)
GAIN
CROSSOVER FREQUENCY = 60.7kHz
PHASE MARGIN = 59°
PHASE
-100
-60
0
80
0
20
40
-50
-20
100K
10K
1K
50
30
10
-10
-30
-40
120
100
60
40
-120
-80
-40
PHASE (°)
2V/div
2μs/div
V
LX
10V/div
MAX17505 5V OUTPUT
APPLICATION OF EXTERNAL CLOCK AT 700kHz
(FIGURE 3 CIRCUIT)
toc31
V
SYNC
MODE = SGND
GAIN (dB)
FREQUENCY (Hz)
MAX17505S 5V OUTPUT
BODE PLOT
(1.7A LOAD CURRENT, FIGURE 5CIRCUIT)
CROSSOVER FREQUENCY = 101kHz
PHASE MARGIN = 58.1°
GAIN
PHASE
toc32a
100
105
104
103
-20
0
20
40
-50
0
50
2V/div
2μs/div
V
LX
10V/div
MAX17505S 5V OUTPUT
APPLICATION OF EXTERNAL CLOCK AT 1.2MHz
(FIGURE 5 CIRCUIT)
V
SYNC
toc31a
MODE = SGND
GAIN (dB)
FREQUENCY (Hz)
toc33
MAX17505 3.3V OUTPUT
BODE PLOT
(1.7A LOAD CURRENT, FIGURE 4 CIRCUIT)
CROSSOVER FREQUENCY = 58kHz
PHASE MARGIN = 59°
PHASE
GAIN
120
-60
0
-80
0
20
40
60
-20
100K
10K
1K
50
30
10
-10
-30
-40
100
80
60
40
20
-20
-40
PHASE (°)
GAIN (dB)
FREQUENCY (Hz)
MAX17505S 3.3V OUTPUT
BODE PLOT
(1.7A LOAD CURRENT, FIGURE 6CIRCUIT)
toc33a
CROSSOVER FREQUENCY = 77.7kHz
PHASE MARGIN = 63.2°
GAIN
PHASE
100
10
5
10
4
10
3
-30
-20
-10
0
10
20
30
40
-50
0
50
Typical Operating Characteristics (continued)
Maxim Integrated
│
14
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
PIN NAME FUNCTION
1–3 VIN
Power-Supply Input. 4.5V to 60V input supply range. Connect the VINpinstogether.DecoupletoPGND
with a 2.2µF capacitor; place the capacitor close to the VINandPGNDpins.RefertotheMAX17505/
MAX17505S EV kit data sheets for a layout example.
4 EN/UVLO
Enable/Undervoltage Lockout. Drive EN/UVLO high to enable the output voltage. Connect to the center
of the resistor-divider between VINandSGNDtosettheinputvoltageatwhichthedeviceturnson.Pull
up to VIN for always-on operation.
5RESET Open-Drain RESET Output. The RESET output is driven low if FB drops below 92% of its set value.
RESET goes high 1024 clock cycles after FB rises above 95% of its set value.
6 SYNC The device can be synchronized to an external clock using this pin. See the External Frequency
Synchronization section for more details.
7 SS Soft-StartInput.ConnectacapacitorfromSStoSGNDtosetthesoft-starttime.
8 CF Atswitchingfrequencieslowerthan500kHz,connectacapacitorfromCFtoFB.LeaveCFopenif
switchingfrequencyisequalormorethan500kHz.SeetheLoop Compensation section for more details.
9 FB FeedbackInput.ConnectFBtothecentertapofanexternalresistor-dividerfromtheoutputtoGNDto
set the output voltage. See the Adjusting Output Voltage section for more details.
10 RT ConnectaresistorfromRTtoSGNDtosettheregulator’sswitchingfrequency.LeaveRTopenforthe
default500kHzfrequency.SeetheSetting the Switching Frequency (RT) section for more details.
11 MODE
MODEpinconguresthedevicetooperateeitherinPWM,PFM,orDCMmodesofoperation.Leave
MODEunconnectedforPFMoperation(pulseskippingatlightloads).ConnectMODEtoSGNDfor
constant-frequency PWM operation at all loads. Connect MODE to VCC for DCM operation. See the
MODE Setting section for more details.
Pin Description
Pin Conguration
19
20
* EXPOSED PAD (CONNECT TO GROUND).
18
17
7
6
8
V
IN
RESET
9
V
IN
PGND
V
CC
MODE
PGND
1 2
LX
4 5
15 14 12 11
LX
BST
FB
CF
SS
SYNC
+
V
IN
SGND
3
13
LX
16 10 RT
PGND
TQFN
4mm × 4mm
MAX17505/
TOP VIEW
EN/UVLO
MAX17505S
Maxim Integrated
│
15
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
PIN NAME FUNCTION
12 VCC 5V LDO Output. Bypass VCCwith2.2µFceramiccapacitancetoSGND.
13 SGND AnalogGround
14–16 PGND
PowerGround.ConnectthePGNDpinsexternallytothepowergroundplane.ConnecttheSGNDand
PGNDpinstogetheratthegroundreturnpathoftheVCCbypasscapacitor.RefertotheMAX17505/
MAX17505S EV kit data sheets for a layout example.
17–19 LX SwitchingNode.ConnectLXpinstotheswitchingsideoftheinductor.RefertotheMAX17505/
MAX17505S EV kit data sheets for a layout example.
20 BST Boost Flying Capacitor. Connect a 0.1µF ceramic capacitor between BST and LX.
— EP
Exposedpad.ConnecttotheSGNDpin.ConnecttoalargecopperplanebelowtheICtoimproveheat
dissipationcapability.Addthermalviasbelowtheexposedpad.RefertotheMAX17505/MAX17505SEV
kit data sheets for a layout example.
Pin Description (continued)
Block Diagram
VCC
SGND
1.215V
5V
LX
PGND
MODE
VIN
BST
LDO
EN/UVLO
RT
MAX17505/MAX17505S
SYNC
CF
FB
SS
FB
OSCILLATOR
SWITCHOVER
LOGIC
ERROR AMPLIFIER/
LOOP COMPENSATION
MODE
SELECTION
LOGIC
SLOPE
COMPENSATION
RESET
LOGIC
CURRENT-SENSE
LOGIC
HICCUP
HICCUP
5µA
VCC
PWM/
PFM/
HICCUP
LOGIC
AND
DRIVERS
VBG = 0.9V
RESET
EN/UVLO
Maxim Integrated
│
16
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Detailed Description
The MAX17505/MAX17505S high-efficiency, high-
voltage, synchro nously rectified step-down converter with
dual integrated MOSFETs operates over a 4.5V to 60V
input. It delivers up to 1.7A and 0.9V to 90%VIN output
voltage. Built-in compensation across the output voltage
range eliminates the need for external components. The
feedback (FB) regulation accuracy over -40NC to +125NC
is ±1.1%.
The device features a peak-current-mode control
architecture. An internal transconductance error amplifier
produces an integrated error voltage at an internal node,
which sets the duty cycle using a PWM comparator, a high-
side current-sense amplifier, and a slope-compensation
generator. At each rising edge of the clock, the high-
side MOSFET turns on and remains on until either
the appropriate or maximum duty cycle is reached, or
the peak current limit is detected. During the high-side
MOSFET’son-time,theinductorcurrentrampsup.During
the second half of the switching cycle, the high-side
MOSFET turns off and the low-side MOSFET turns on.
The inductor releases the stored energy as its current
ramps down and provides current to the output.
The device features a MODE pin that can be used to operate
the device in PWM, PFM, or DCN control schemes. The
device integrates adjustable-input undervoltage lockout,
adjustablesoft-start,openRESET, and external frequency
synchronization features. The MAX17505S offers a
lower Minimum On-Time that allows for higher switching
frequencies and a smaller solution size.
Mode Selection (MODE)
The logic state of the MODE pin is latched when VCC
and EN/UVLO voltages exceed the respective UVLO
rising thresholds and all internal voltages are ready to
allow LX switching. If the MODE pin is open at power-up,
the device operates in PFM mode at light loads. If the
MODE pin is grounded at power-up, the device operates
in constant-frequency PWM mode at all loads. Finally,
if the MODE pin is connected to VCC at power-up, the
device operates in constant-frequency DCM mode at light
loads. State changes on the MODE pin are ignored during
normal operation.
PWM Mode Operation
In PWM mode, the inductor current is allowed to go
negative. PWM operation provides constant frequency
operation at all loads, and is useful in applications
sensitive to switching frequency. However, the PWM
mode of operation gives lower efficiency at light loads
compared to PFM and DCM modes of operation.
PFM Mode Operation
PFM mode of operation disables negative inductor current
and additionally skips pulses at light loads for high
efficiency. In PFM mode, the inductor current is forced to
a fixed peak of 750mA every clock cycle until the output
rises to 102.3% of the nominal voltage. Once the output
reaches 102.3% of the nominal voltage, both the high-side
and low-side FETs are turned off and the device enters
hibernate operation until the load discharges the output to
101.1% of the nominal voltage. Most of the internal blocks
are turned off in hibernate operation to save quiescent
current. After the output falls below 101.1% of the nominal
voltage, the device comes out of hibernate operation,
turns on all internal blocks, and again commences the
process of delivering pulses of energy to the output until it
reaches 102.3% of the nominal output voltage.
The advantage of the PFM mode is higher efficiency at
light loads because of lower quiescent current drawn from
supply. The disadvantage is that the output-voltage ripple
is higher compared to PWM or DCM modes of operation
and switching frequency is not constant at light loads.
DCM Mode Operation
DCM mode of operation features constant frequency
operation down to lighter loads than PFM mode, by not
skipping pulses but only disabling negative inductor cur-
rent at light loads. DCM operation offers efficiency perfor-
mance that lies between PWM and PFM modes.
Linear Regulator (VCC)
An internal linear regulator (VCC) provides a 5V nominal
supply to power the internal blocks and the low-side
MOSFET driver. The output of the linear regulator (VCC)
should be bypassed with a 2.2µF ceramic capacitor to
SGND. The device employs an undervoltage lockout
circuit that disables the internal linear regulator when VCC
falls below 3.8V (typ).
Setting the Switching Frequency (RT)
The switching frequency of the device can be programmed
from 100kHz to 2.2MHz by using a resistor connected
fromtheRTpintoSGND.Theswitchingfrequency(fSW)
isrelatedtotheresistorconnectedattheRTpin(RRT) by
the following equation:
3
RT
SW
21 10
R 1.7
f
×
≅−
whereRRTisinkΩandfSWisinkHz.LeavingtheRTpin
open causes the device to operate at the default switching
frequencyof500kHz.SeeTable 1forRTresistorvalues
for a few common switching frequencies.
Maxim Integrated
│
17
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Operating Input Voltage Range
The minimum and maximum operating input voltages for
a given output voltage should be calculated as follows:
OUT OUT(MAX) DCR
IN(MIN) SW(MAX) OFF(MAX)
OUT(MAX)
V (I (R 0.15))
V1- (f t )
(I 0.175)
+ ×+
=×
+×
OUT
IN(MAX) SW(MAX) ON(MIN)
V
Vf t)
=×
where VOUT is the steady-state output voltage, IOUT (MAX)
isthemaximumloadcurrent,RDCR is the DC resistance
of the inductor, fSW(MAX) is the maximum switching
frequency, tOFF-MAX is the worst-case minimum switch
off-time (160ns), and tON-MIN is the worst-case minimum
switch on-time (135ns for the MAX17505, 80ns for the
MAX17505S).
External Frequency Synchronization (SYNC)
The internal oscillator of the device can be synchronized
to an external clock signal on the SYNC pin. The external
synchronization clock frequency must be between 1.1
x fSW and 1.4 x fSW, where fSW is the frequency
programmed by the RT resistor. The minimum external
clock pulse-width high should be greater than 50ns. See
the RT AND SYNC section in the Electrical Characteristics
table for details.
Overcurrent Protection/Hiccup Mode
The device is provided with a robust overcurrent protection
scheme that protects the device under overload and
output short-circuit conditions. A cycle-by-cycle peak
current limit turns off the high-side MOSFET whenever
the high-side switch current exceeds an internal limit
of 2.8A (typ). A runaway current limit on the high-side
switch current at 3.4A (typ) protects the device under
high input voltage, short-circuit conditions when there is
insufficient output voltage available to restore the inductor
current that was built up during the ON period of the
step-down converter. One occurrence of the runaway
current limit triggers a hiccup mode. In addition, if due to
a fault condition, feedback voltage drops to 0.58V (typ)
any time after soft-start is complete, and hiccup mode
is triggered. In hiccup mode, the converter is protected
by suspending switching for a hiccup timeout period of
32,768 clock cycles. Once the hiccup timeout period
expires, soft-start is attempted again. Note that when soft-
start is attempted under overload condition, if feedback
voltage does not exceed 0.58V, the device switches at
halftheprogrammed switchingfrequency.Hiccup mode
of operation ensures low power dissipation under output
short-circuit conditions.
RESET Output
The device includes a RESET comparator to monitor the
output voltage. The open-drain RESET output requires
an external pullup resistor. RESET goes high (high
impedance) 1024 switching cycles after the regulator
output increases above 95% of the designed nominal
regulated voltage. RESET goes low when the regulator
output voltage drops to below 92% of the nominal
regulated voltage. RESET also goes low during thermal
shutdown.
Prebiased Output
When the device starts into a prebiased output, both the
high-side and the low-side switches are turned off so that
theconverterdoesnotsinkcurrentfromtheoutput.High-
side and low-side switches do not start switching until
the PWM comparator commands the first PWM pulse, at
which point switching commences. The output voltage is
then smoothly ramped up to the target value in alignment
with the internal reference.
Thermal-Shutdown Protection
Thermal-shutdown protection limits total power dissipation
inthedevice.Whenthejunctiontemperatureofthedevice
exceeds +165ºC, an on-chip thermal sensor shuts down
the device, allowing the device to cool. The thermal sensor
turnsthe device on againafter the junctiontemperature
cools by 10ºC. Soft-start resets during thermal shutdown.
Carefully evaluate the total power dissipation (see the
Power Dissipation section) to avoid unwanted triggering of
the thermal shutdown in normal operation.
Table 1. Switching Frequency vs. RT
Resistor
SWITCHING FREQUENCY (kHz) RT RESISTOR (kΩ)
500 Open
100 210
200 102
400 49.9
1000 19.1
2200 8.06
Maxim Integrated
│
18
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Applications Information
Input Capacitor Selection
The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the circuit’s switching.
The input capacitor RMS current requirement (IRMS) is
defined by the following equation:
×
= ×
OUT IN OUT
RMS OUT(MAX) IN
V (V - V )
II V
where, IOUT(MAX) is the maximum load current. IRMS has
a maximum value when the input voltage equals twice
the output voltage (VIN = 2 x VOUT), so IRMS(MAX) =
IOUT(MAX)/2.
Choose an input capacitor that exhibits less than +10ºC
temperature rise at the RMS input current for optimal
long-termreliability.Uselow-ESRceramiccapacitorswith
high-ripple-currentcapabilityattheinput.X7Rcapacitors
are recommended in industrial applications for their
temperature stability. Calculate the input capacitance
using the following equation:
××
=η× ×∆
OUT(MAX)
IN
SW IN
I D (1- D)
CfV
where D = VOUT/VIN is the duty ratio of the controller,
fSWistheswitchingfrequency,ΔVIN is the allowable input
voltage ripple, and E is the efficiency.
In applications where the source is located distant from
the device input, an electrolytic capacitor should be
added in parallel to the ceramic capacitor to provide
necessary damping for potential oscillations caused by
the inductance of the longer input power path and input
ceramic capacitor.
Inductor Selection
Three key inductor parameters must be specified for
operation with the device: inductance value (L), inductor
saturation current (ISAT),andDCresistance(RDCR). The
switching frequency and output voltage determine the
inductor value as follows:
OUT
SW
V
Lf
=
where VOUT, and fSW are nominal values. Select an
inductor whose value is nearest to the value calculated by
the previous formula.
Select a low-loss inductor closest to the calculated
value with acceptable dimensions and having the lowest
possible DC resistance. The saturation current rating
(ISAT) of the inductor must be high enough to ensure that
saturation can occur only above the peak current-limit
value of 2.8A.
Output Capacitor Selection
X7Rceramicoutputcapacitorsarepreferredduetotheir
stability over temperature in industrial applications. The
output capacitors are usually sized to support a step load
of 50% of the maximum output current in the application,
so the output voltage deviation is contained to 3% of the
output voltage change. The minimum required output
capacitance can be calculated as follows:
×
= × ∆
STEP RESPONSE
OUT
OUT
It
1
C2V
≅+
RESPONSE C sw
0.33 1
t ()
ff
where ISTEP is the load current step, tRESPONSE is the
response time of the controller, DVOUT is the allowable
output-voltage deviation, fC is the target closed-loop crossover
frequency, and fSW is the switching frequency. For the
MAX17505, select fC to be 1/9th of fSW if the switching
frequency is less than or equal to 500kHz. If the switching
frequencyismorethan500kHz,selectfCtobe55kHz.For
the MAX17505S, select fC to be 1/10th of fSW if the switching
frequency is less than or equal to 1MHz. If the switching
frequencyismorethan1MHz,selectfCtobe100kHz.
Derating of ceramic capacitors with DC-voltage must be
considered while selecting the output capacitor. Derating
curvesareavailablefromallmajorceramiccapacitorvendors.
Soft-Start Capacitor Selection
The device implements adjustable soft-start operation to
reduce inrush current. A capacitor connected from the SS pin
toSGNDprogramsthesoft-starttime.Theselectedoutput
capacitance (CSEL) and the output voltage (VOUT) determine
the minimum required soft-start capacitor as follows:
-6
SS SEL OUT
C 28 10 C V
≥× × ×
The soft-start time (tSS) is related to the capacitor
connected at SS (CSS) by the following equation:
SS
SS -6
C
t
5.55 10
=
×
For example, to program a 1ms soft-start time, a 5.6nF
capacitorshouldbeconnectedfromtheSSpintoSGND.
Maxim Integrated
│
19
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Setting the Input Undervoltage-Lockout Level
Thedeviceoffersanadjustableinputundervoltage-lockout
level. Set the voltage at which the device turns on with
a resistive voltage-divider connected from VIN to SGND.
Connect the center node of the divider to EN/UVLO.
ChooseR1tobe3.3MIandthencalculateR2asfollows:
×
=
INU
R1 1.215
R2 (V - 1.215)
where VINU is the voltage at which the device is required
to turn on. Ensure that VINU is higher than 0.8 x VOUT. If
the EN/UVLO pin is driven from an external signal source,
aseriesresistanceofminimum1kΩisrecommendedto
be placed between the signal source output and the EN/
UVLO pin, to reduce voltage ringing on the line.
Loop Compensation
The device is internally loop compensated. However, if
theswitchingfrequencyislessthan500kHz,connecta
0402 capacitor C6 between the CF pin and the FB pin.
Use Table 2 to select the value of C6.
Adjusting Output Voltage
Set the output voltage with a resistive voltage-divider
connected from the positive terminal of the output
capacitor (VOUT)toSGND(seeFigure2).Connectthe
center node of the divider to the FB pin. Use the following
procedure to choose the resistive voltage-divider values:
Calculate resistor R3 from the output to the FB pin as
follows:
3
C OUT
216 10
R3 fC
×
=×
whereR3isinkΩ,crossoverfrequencyfCisinkHz,and
the output capacitor COUT is in µF. For the MAX17505,
choose fC to be 1/9th of the switching frequency, fSW, if
theswitchingfrequencyislessthanorequalto500kHz.
Iftheswitchingfrequencyismorethan500kHz,selectfC
tobe55kHz.FortheMAX17505S,selectfC to be 1/10th
of fSW if the switching frequency is less than or equal
to1MHz.Iftheswitchingfrequencyismorethan1MHz,
select fCtobe100kHz.
Figure 1. Setting the Input Undervoltage Lockout Figure 2. Setting the Output Voltage
Table 2. C6 Capacitor Value at Various Switching Frequencies
SWITCHING FREQUENCY RANGE (kHz) C6 (pF)
200 to 300 2.2
300 to 400 1.2
400 to 500 0.75
R3
R4
SGND
FB
VOUT
R1
R2
SGND
EN/UVLO
VIN
Maxim Integrated
│
20
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
CalculateresistorR4fromtheFBpintoSGNDasfollows
:
×
=
OUT
R3 0.9
R4 (V - 0.9)
Power Dissipation
At a particular operating condition, the power losses that
lead to temperature rise of the part are estimated as
follows:
()
=××
η
2
LOSS OUT DCR
OUT
1
P (P ( - 1)) - I R
= ×
OUT OUT OUT
P VI
where POUT is the total output power, η is the efficiency
of the converter, and RDCR is the DC resistances of the
inductor. (See the Typical Operating Characteristics for more
information on efficiency at typical operating conditions.)
For a multilayer board, the thermal performance metrics
for the package are given below:
JA 33 C Wθ=°
JC 2CWθ=°
Thejunctiontemperatureofthedevicecanbeestimated
at any given maximum ambient temperature (TA_MAX)
from the equation below:
( )
= +θ ×
J_MAX A_MAX JA LOSS
TT P
If the application has a thermal management system that
ensures that the exposed pad of the device is maintained
at a given temperature (TEP_MAX) by using proper heat
sinks,thenthejunctiontemperatureofthedevicecanbe
estimated at any given maximum ambient temperature
from the equation below:
( )
= +θ ×
J_MAX EP_MAX JC LOSS
TT P
Junction temperature greater than +125°C degrades
operating lifetimes.
PCB Layout Guidelines
All connections carrying pulsed currents must be very
short and as wide as possible. The inductance of these
connections must be kept to an absolute minimum due to
the high di/dt of the currents. Since inductance of a current
carrying loop is proportional to the area enclosed by the
loop, if the loop area is made very small, inductance is
reduced. Additionally, small-current loop areas reduce
radiated EMI.
A ceramic input filter capacitor should be placed close
to the VIN pins of the IC. This eliminates as much trace
inductance effects as possible and gives the IC a cleaner
voltage supply. A bypass capacitor for the VCC pin also
should be placed close to the pin to reduce effects of trace
impedance.
When routing the circuitry around the IC, the analog
small-signal ground and the power ground for switching
currents must be kept separate. They should be connected
together at a point where switching activity is at a
minimum, typically the return terminal of the VCC bypass
capacitor. This helps keep the analog ground quiet.
The ground plane should be kept continuous/unbroken
as far as possible. No trace carrying high switching
current should be placed directly over any ground plane
discontinuity.
PCB layout also affects the thermal performance of the
design. A number of thermal vias that connect to a large
ground plane should be provided under the exposed pad
of the part, for efficient heat dissipation.
For a sample layout that ensures first pass success,
refer to the MAX17505 evaluation kit layout available at
www.maximintegrated.com.
Maxim Integrated
│
21
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Recommended Component Placement for MAX17505/MAX17505S
R1
R2
C5
R6
C3 C6
R4
R5
R3
C2
VOUT
PLANE
VIN PLANE
C4
PGND PLANE
SYNC
SGND PLANE
MODE
SGND
PGND PLANE
MAX17505/
MAX17505S
LX PLANE
LX PLANE
L1
C1
Maxim Integrated
│
22
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Figure 3. MAX17505 Typical Application Circuit (5V, 500kHz Switching Frequency)
Figure 4. MAX17505 Typical Application Circuit (3.3V, 500kHz Switching Frequency)
RESET
VIN VIN VIN
BSTRT
SYNC
MODE
VCC
SGND
CF SS
FB
PGNDPGNDPGND
LX
LX
LX
VIN (4.5V TO 60V)
EN/UVLO
MAX17505
L1
6.8µH
C5
0.1µF
C4
47µF R3
127kΩ
R4
47.5kΩ
VOUT
3.3V, 1.7A
C1
2.2uF
C3
5600pF
C2
2.2µF
fSW = 500kHz
VIN
L1 = 6.8µH (XAL6060-682ME)
C4 = 47µF (MURATA GRM32ER71A476K)
RESET
VIN VIN VIN
BSTRT
SYNC
MODE
VCC
SGND
CF SS
FB
PGNDPGNDPGND
LX
LX
LX
EN/UVLO
MAX17505
L1
10µH
C5
0.1µF
C4
22µF R3
178kΩ
R4
39kΩ
VOUT
5V, 1.7A
VIN
(6.5V TO 60V)
C1
2.2µF
C3
5.6nF
C2
2.2µF
fSW = 500kHz
L1 = 10µH (XAL6060-103ME)
C4 = 22µF (MURATA GRM32ER71A226K)
Maxim Integrated
│
23
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Figure 6. MAX17505S Typical Application Circuit (3.3V Output, 1MHz Switching Frequency)
Figure 5. MAX17505S Typical Application Circuit (5V Output, 1MHz Switching Frequency)
RT
SYNC
MODE
V
CC
SGND
BST
LX
FB
RESET
LX
LX
CF SS PGND PGND PGND
V
IN
V
IN
V
IN
EN/UVLO
C4
C2
2.2µF
C3
5.6nF
R3
196KΩ
R4
43.2KΩ
10µF
4.7µH
L1
C5
0.1µF
C1
2.2µF
MAX17505S
V
OUT
5V,1.7A
V
IN
L1 = 4.7µH (XAL4030, 4mm x 4mm)
R5
19.1KΩ
f
SW
= 1MHz
C4 = 10µH (MURATA GRM32DR71A106KA01)
RT
SYNC
MODE
V
CC
SGND
BST
LX
FB
LX
LX
CF SS PGND PGND PGND
V
IN
V
IN
V
IN
EN/UVLO
C4
C2
2.2µF
C3
5.6nF
R3
115KΩ
R4
43.2KΩ
22µF
3.3µH
L1
C5
0.1µF
C1
2.2µF
MAX17505S
V
OUT
3.3V,1.7A
V
IN
L1 = 3.3µH (XAL4030, 4mm x 4mm)
R5
19.1KΩ
f
SW =
1MHz
RESET
C4 = 22µH (MURATA GRM32ER71A226KE20)
Maxim Integrated
│
24
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Note: Device operates over the -40ºC to +125ºC temperature
range, unless otherwise noted.
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
PART PIN-PACKAGE
MAX17505ATP+ 20 TQFN (4mm x 4mm)
MAX17505SATP+ 20 TQFN-EP* (4mm x 4mm)
Chip Information
PROCESS:BiCMOS
Ordering Information
Maxim Integrated
│
25
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
www.maximintegrated.com
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 1/14 Initial release —
1 10/16 Added MAX17505S to data sheet 1–17
2 5/17 Updated part number in title and TOCs 8a, 12, 12a, 13, 13a, 14a, 15a, 16a, 17a, 18,
18a, 19a, 20a, 21a, 22, 22a, 23, 23a, 24a, 25a, 26a, 27a, 29a, 31, and 31a 1–27
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim
reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits) shown in the Electrical Character-
istics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
© 2017 Maxim Integrated Products, Inc.
│
26
MAX17505 4.5V-60V, 1.7A, High-Efciency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Mouser Electronics
Authorized Distributor
Click to View Pricing, Inventory, Delivery & Lifecycle Information:
Maxim Integrated:
MAX17505EVKITA# MAX17505EVKITB# MAX17505ATP+ MAX17505ATP+T MAX17505SATP+
MAX17505SATP+T