EVALUATION KIT AVAILABLE
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
General Description
The MAX17505/MAX17505S high-efficiency, highvoltage, synchronously 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 discontinuousconduction 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 inputvoltage level. An open-drain RESET pin provides a
delayed power-good signal to the system 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
19-6907; Rev 2; 5/17
Benefits and Features
●● Eliminates External Components and Reduces Total
Cost
• No Schottky-Synchronous Operation for High
Efficiency 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 Efficiency > 90%
• PFM and DCM Modes for High Light-Load Efficiency
• 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
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
Absolute Maximum Ratings (Note 1)
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,
RT to 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
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.
Package Information
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
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 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.
Note 1: Junction temperature greater than +125°C degrades operating lifetimes.
Electrical Characteristics
(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
60
V
2.8
4.5
INPUT SUPPLY (VIN)
Input Voltage Range
Input Shutdown Current
VIN
IIN-SH
VFB = 1V, MODE = RT = open
118
VFB = 1V, MODE = open
162
IQ-DCM
DCM mode, VLX = 0.1V
1.16
IQ_PWM
Normal switching mode, fSW = 500kHz, VFB
= 0.8V
9.5
IQ_PFM
Input Quiescent Current
www.maximintegrated.com
4.5
VEN/UVLO = 0V (shutdown mode)
µA
1.8
mA
Maxim Integrated │ 2
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Electrical Characteristics (continued)
(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)
VENR
VEN/UVLO rising
1.19
1.215
1.24
VENF
VEN/UVLO falling
1.068
1.09
1.111
-50
0
+50
nA
4.75
5
5.25
V
VCC = 4.3V, VIN = 6V
26.5
54
100
mA
VIN = 4.5V, IVCC = 20mA
4.2
VCC_UVR
VCC rising
4.05
4.2
4.3
VCC_UVF
VCC falling
3.65
3.8
3.9
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
VSS = 0.5V
4.7
5.3
µA
MODE = SGND on VCC
0.89
0.9
0.91
MODE = OPEN
0.89
0.915
0.936
0 < VFB < 1V, TA = +25ºC
-50
EN/UVLO Threshold
EN/UVLO Input Leakage Current
IEN
VEN/UVLO = 0V, TA = +25ºC
V
LDO
VCC Output Voltage Range
VCC
VCC Current Limit
IVCC-MAX
VCC Dropout
VCC-DO
VCC UVLO
6V < VIN < 60V, IVCC = 1mA
1mA ≤ IVCC ≤ 25mA
V
V
POWER MOSFET AND BST DRIVER
SOFT-START (SS)
Charging Current
ISS
5
FEEDBACK (FB)
FB Regulation Voltage
VFB_REG
FB Input Bias Current
IFB
+50
V
nA
MODE
MODE Threshold
VM-DCM
MODE = VCC (DCM mode)
VM-PFM
MODE = open (PFM mode)
VM-PWM
MODE = GND (PWM mode)
VCC 1.6
V
VCC / 2
1.4
CURRENT LIMIT
Peak Current-Limit Threshold
Runaway Current-Limit Threshold
IPEAK-LIMIT
2.4
2.8
3.25
A
IRUNAWAY-LIMIT
2.9
3.4
3.9
A
0
+0.16
Valley Current-Limit Threshold
ISINK-LIMIT
PFM Current-Limit Threshold
IPFM
www.maximintegrated.com
MODE = open/VCC
-0.16
MODE = GND
MODE = open
-1.8
0.6
0.75
0.9
A
A
Maxim Integrated │ 3
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Electrical Characteristics (continued)
(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
RRT = 210kΩ
90
100
110
RRT = 102kΩ
180
200
220
RRT = 40.2kΩ
475
500
525
RRT = 8.06kΩ
1950
2200
2450
RRT = open
460
500
540
fSW set by RRT
1.1 x
fSW
UNITS
RT AND SYNC
Switching Frequency
fSW
SYNC Frequency Capture Range
SYNC Pulse Width
SYNC Threshold
FB Undervoltage Trip Level to
Cause Hiccup
50
VIH
0.8
VFB-HICF
0.56
(Note 3)
Minimum On-Time
tON-MIN
Minimum Off-Time
tOFF-MIN
MAX17505
55
140
LX Dead Time
0.6
RESET Output Level Low
IRESET = 10mA
RESET Output Leakage Current
TA = TJ = +25ºC, VRESET = 5.5V
VFB-OKF
VFB-OKR
VFB falling
VFB rising
RESET Deassertion Delay After FB
Reaches 95% Regulation
90.5
93.8
92
95
V
135
ns
80
ns
160
ns
ns
0.4
-0.1
V
Cycles
5
RESET
FB Threshold for RESET
Deassertion
0.58
32,768
MAX17505S
kHz
ns
2.1
VIL
Hiccup Timeout
FB Threshold for RESET Assertion
1.4 x
fSW
kHz
V
+0.1
µA
94
%VFB-
97.2
%VFB-
REG
REG
1024
Cycles
165
ºC
10
ºC
THERMAL SHUTDOWN
Thermal-Shutdown Threshold
Temperature rising
Thermal-Shutdown Hysteresis
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.
www.maximintegrated.com
Maxim Integrated │ 4
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics
(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.)
MAX17505 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PWM MODE, FIGURE 3 CIRCUIT)
MAX17505S 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PWM MODE, FIGURE 5 CIRCUIT)
toc01
100
100
100
80
VIN = 24V
70
VIN = 36V
VIN = 48V
VIN = 12V
60
70
VIN = 24V
EFFICIENCY (%)
80
toc02
90
80
EFFICIENCY (%)
EFFICIENCY (%)
toc01a
90
90
VIN = 36V VIN = 48V
60
VIN = 12V
50
70
VIN = 48V
VIN = 36V
60
VIN = 24V
50
40
VIN = 12V
30
20
50
40
MODE = SGND
40
MAX17505 3.3V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PWM MODE, FIGURE 4 CIRCUIT)
0
500
1000
1500
30
1700
LOAD CURRENT (mA)
0
500
1000
0
1700
1500
100
toc02a
EFFICIENCY (%)
80
70
VIN = 36V
VIN = 24V
1000
1500
1700
VIN = 48V
toc03
100
80
VIN = 12V
70
VIN = 36V
VIN = 48V
VIN = 24V
60
VIN = 12V
50
40
40
30
MODE = OPEN
MODE = SGND
20
500
MAX17505 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PfM MODE, FIGURE 3 CIRCUIT)
90
50
0
LOAD CURRENT (mA)
90
60
MODE = SGND
LOAD CURRENT (mA)
MAX17505S 3.3V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PWM MODE, FIGURE 6 CIRCUIT)
EFFICIENCY (%)
10
MODE = SGND
0
500
1000
1500
30
1700
1
10
LOAD CURRENT (mA)
LOAD CURRENT (mA)
MAX17505S 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(PFM MODE, FIGURE 5 CIRCUIT)
100
1000 1700
100
MAX17505 3.3V OUTPUT
EFFICIENCY VS. LOAD CURRENT
(PFM MODE, FIGURE 4 CIRCUIT)
toc03a
toc04
100
90
90
80
70
EFFICIENCY (%)
EFFICIENCY (%)
80
VIN = 48V
60
VIN = 12V
VIN = 24V
VIN = 36V
50
60
40
VIN = 24V
VIN = 12V
20
10
MODE = OPEN
10
100
LOAD CURRENT (mA)
www.maximintegrated.com
1000
1700
0
VIN = 48V
VIN = 36V
50
30
40
30
70
MODE = OPEN
1
10
100
1000 1700
LOAD CURRENT (mA)
Maxim Integrated │ 5
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(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.)
MAX17505S 3.3V OUTPUT
EFFICIENCY VS. LOAD CURRENT
(PFM MODE, FIGURE 6 CIRCUIT)
100
MAX17505 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(DCM MODE, FIGURE 3 CIRCUIT)
toc04a
100
MAX17505S 5V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(DCM MODE, FIGURE 5 CIRCUIT)
toc05
VIN = 48V
60
50
VIN = 24V
VIN = 12V
VIN = 36V
60
VIN = 12V
40
30
MODE = OPEN
100
30
1700
1000
MAX17505 3.3V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(DCM MODE, FIGURE 4 CIRCUIT)
100
80
10
100
toc06
100
100
VIN = 12V
1000
toc06a
VIN = 48V
VIN = 36V
80
VIN = 24V
30
70
VIN = 24V
60
VIN = 12V
50
40
20
10
30
MODE = VCC
1
10
20
1000 1700
100
1000 1700
100
MAX17505 5V OUTPUT
LOAD AND LINE REGULATION
(PWM MODE, FIGURE 3 CIRCUIT)
MAX17505S 5V OUTPUT
LOAD AND LINE REGULATION
(PWM MODE, FIGURE 5 CIRCUIT)
toc07
5.02
5.00
OUTPUT VOLTAGE (V)
5.01
5.03
5.02
5.01
VIN = 12V
VIN = 24V VIN = 36V
VIN = 48V
4.99
4.98
4.97
4.96
VIN = 24V
4.98
4.97
4.96
4.95
VIN = 12V
500
1000
LOAD CURRENT (mA)
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1500
VIN = 36V
4.93
MODE = SGND
1700
toc07a
VIN = 48V
4.99
4.94
0
10
LOAD CURRENT (mA)
5.04
5.00
MODE = VCC
1
LOAD CURRENT (mA)
5.05
OUTPUT VOLTAGE (V)
10
90
40
4.95
1
MAX17505S 3.3V OUTPUT
EFFICIENCY vs. LOAD CURRENT
(DCM MODE, FIGURE 6 CIRCUIT)
60
0
MODE = VCC
LOAD CURRENT (mA)
VIN = 36V
50
10
1000 1700
EFFICIENCY (%)
EFFICIENCY (%)
1
VIN = 48V
90
20
MODE = VCC
LOAD CURRENT (mA)
LOAD CURRENT (mA)
70
VIN = 12V
50
40
10
VIN = 24V
60
50
40
30
VIN = 24V
70
70
EFFICIENCY (%)
EFFICIENCY (%)
EFFICIENCY (%)
70
VIN = 36V
80
VIN = 36V
80
80
VIN = 48V
90
90
90
toc05a
100
VIN = 48V
4.92
MODE = SGND
0
500
1000
1500 1700
LOAD CURRENT (mA)
Maxim Integrated │ 6
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(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.)
MAX17505S 3.3V OUTPUT
LOAD AND LINE REGULATION
(PWM MODE, FIGURE 6 CIRCUIT)
MAX17505 3.3V OUTPUT
LOAD AND LINE REGULATION
(PWM MODE, FIGURE 4 CIRCUIT)
toc08
3.36
3.33
3.32
3.31
VIN = 48V
VIN = 24V
3.30
3.29
3.28
3.27
0
500
5.3
3.40
VIN = 48V
VIN = 24V
3.35
3.30
3.25
VIN = 12V
VIN = 36V
3.20
3.10
1500 1700
1000
LOAD CURRENT (mA)
0
500
1000
VIN = 48V
4.5
MODE = OPEN
0
OUTPUT VOLTAGE (V)
5.05
5.00
4.95
VIN = 24V
VIN = 36V
4.85
4.80
toc10
VIN = 48V
500
3.33
3.32
3.31
3.27
1000
1500
1700
toc10a
toc11
2400
2200
SWITCHING FREQUENCY (kHz)
VIN = 12V
3.40
3.30
3.20
VIN = 36V
VIN = 24V
3.10
MODE = OPEN
500
1000
LOAD CURRENT (mA)
www.maximintegrated.com
500
SWITCHING FREQUENCY
vs. RT RESISTANCE
VIN = 48V
0
MODE = OPEN
0
LOAD CURRENT (mA)
MAX17505S 3.3V OUTPUT
LOAD AND LINE REGULATION
(PFM MODE, FIGURE 6 CIRCUIT)
3.50
VIN = 36V
3.30
LOAD CURRENT (mA)
3.60
VIN = 24V
3.28
1500 1700
1000
VIN = 12V
3.34
3.29
MODE = OPEN
0
1500 1700
3.35
VIN = 12V
4.90
1000
3.37
VIN = 48V
5.10
500
MAX17505 3.3V OUTPUT
LOAD AND LINE REGULATION
(PFM MODE, FIGURE 4 CIRCUIT)
3.36
5.15
OUTPUT VOLTAGE (V)
4.8
LOAD CURRENT (mA)
toc09a
5.20
OUTPUT VOLTAGE (V)
4.9
LOAD CURRENT (mA)
5.25
3.00
5.0
1500 1700
MAX17505S 5V OUTPUT
LOAD AND LINE REGULATION
(PFM MODE, FIGURE 5 CIRCUIT)
4.75
5.1
4.6
MODE = SGND
MODE = SGND
VIN = 36V
VIN = 24V
VIN = 12V
5.2
4.7
3.15
VIN = 36V
VIN = 12V
toc09
5.4
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.5
3.45
3.34
3.26
toc08a
3.50
3.35
MAX17505 5V OUTPUT
LOAD AND LINE REGULATION
(PFM MODE, FIGURE 3 CIRCUIT)
1500 1700
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0
20
40
60
80
100
RRT (kΩ)
Maxim Integrated │ 7
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(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.)
MAX17505S 5V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(1.7A LOAD CURRENT, FIGURE 5 CIRCUIT)
MAX17505 5V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(1.7A LOAD CURRENT, FIGURE 3 CIRCUIT)
toc12a
toc12
VEN/UVLO
2V/div
VEN/UVLO
VOUT
2V/div
VOUT
2V/div
IOUT
1A/div
IOUT
1A/div
5V/div
VRESET
MODE = SGND
5V/div
VRESET
5V/div
MODE = SGND
1ms/div
1ms/div
MAX17505 3.3V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(1.7A LOAD CURRENT, FIGURE 4 CIRCUIT)
MAX17505S 3.3V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(1.7A LOAD CURRENT, FIGURE 6 CIRCUIT)
toc13
toc13a
VEN/UVLO
2V/div
VOUT
2V/div
IOUT
1A/div
VRESET
5V/div
MODE = SGND
VEN/UVLO
5V/div
VOUT
2V/div
IOUT
1A/div
5V/div
VRESET
MODE = SGND
1ms/div
1mS/div
MAX17505 5V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(PFM MODE, 5mA LOAD CURRENT, FIGURE 3 CIRCUIT)
toc14
MAX17505S 5V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(PFM MODE, 5MA LOAD CURRENT, FIGURE 5 CIRCUIT)
toc14a
MODE = OPEN
2V/div
VEN/UVLO
VEN/UVLO
5V/div
1V/div
VOUT
VRESET
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VOUT
5V/div
2mS/div
VRESET
1V/div
MODE = OPEN
2mS/div
5V/div
Maxim Integrated │ 8
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(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.)
MAX17505 3.3V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(PFM MODE, 5mA LOAD CURRENT, FIGURE 4 CIRCUIT)
toc15a
toc15
VEN/UVLO
MAX17505S 3.3V OUTPUT
SOFT-START/SHUTDOWN FROM EN/UVLO
(PFM MODE, 5mA LOAD CURRENT, FIGURE 6 CIRCUIT)
2V/div
VEN/UVLO
5/div
1V/div
VOUT
1V/div
VOUT
VRESET
5V/div
VRESET
MODE = OPEN
5V/div
MODE = OPEN
2ms/div
2mS/div
MAX17505 5V OUTPUT
SOFT-START WITH 2.5V PREBIAS
(PWM MODE, FIGURE 3 CIRCUIT)
MAX17505S 5V OUTPUT
SOFT-START WITH 2.5V PREBIAS
(PWM MODE, FIGURE 5 CIRCUIT)
toc16
toc16a
5V/div
2V/div
VEN/UVLO
VEN/UVLO
2V/div
2V/div
VOUT
5V/div
VRESET
VOUT
5V/div
VRESET
MODE = SGND
MODE = SGND
1mS/div
1mS/div
MAX17505S 3.3V OUTPUT
SOFT-START WITH 2.5V PREBIAS
(PWM MODE, FIGURE 6 CIRCUIT)
MAX17505 3.3V OUTPUT
SOFT-START WITH 2.5V PREBIAS
(PFM MODE, FIGURE 4 CIRCUIT)
toc17a
toc17
2V/div
VEN/UVLO
VEN/UVLO
5V/div
1V/div
1V/div
VOUT
5V/div
VRESET
MODE = OPEN
1ms/div
www.maximintegrated.com
VOUT
VRESET
5V/div
MODE = OPEN
1mS/div
Maxim Integrated │ 9
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(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.)
MAX17505 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(1.7A LOAD CURRENT, FIGURE 3 CIRCUIT)
MAX17505S 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(1.7A LOAD CURRENT, FIGURE 5 CIRCUIT)
toc18
toc18a
MAX17505 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(PWM MODE, NO LOAD, FIGURE 3 CIRCUIT)
toc19
MODE = SGND
20mV/div
VOUT (AC)
VOUT (AC)
10V/div
VLX
50mV/div
VLX
10V/div
ILX
ILX
MODE = SGND
1A/div
1A/div
VOUT (AC)
20mV/div
VLX
10V/div
ILX
1A/div
MODE = SGND
1μs/div
1μs/div
400nS/div
MAX17505 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(PFM MODE, 25mA LOAD, FIGURE 3 CIRCUIT)
MAX17505S 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(NO LOAD CURRENT, FIGURE 5 CIRCUIT)
toc20
toc19a
MODE = SGND
VOUT (AC)
50mV/div
100mV/div
VOUT (AC)
VLX
10V/div
VLX
10V/div
ILX
500mA/div
ILX
500mA/div
MODE = OPEN
10μs/div
400ns/div
MAX17505S 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(PFM MODE, 25mA LOAD CURRENT, FIGURE 5 CIRCUIT)
MAX17505 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(DCM MODE, 25mA LOAD, FIGURE 3 CIRCUIT)
toc21
toc20a
VOUT (AC)
100mV/div
20mV/div
VOUT (AC)
MODE = VCC
VLX
10V/div
ILX
500mA/div
VLX
10V/div
ILX
200mA/div
MODE = OPEN
4μs/div
www.maximintegrated.com
1μs/div
Maxim Integrated │ 10
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(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.)
MAX17505S 5V OUTPUT
STEADY-STATE SWITCHING WAVEFORMS
(DCM MODE, 25mA LOAD CURRENT, FIGURE 5 CIRCUIT)
toc21a
VOUT (AC)
toc22a
toc22
20mV/div
MODE = VCC
VLX
MAX17505S 5V OUTPUT
LOAD CURRENT STEPPED FROM 0.85A TO 1A
(PWM MODE, FIGURE 5 CIRCUIT)
MAX17505 5V OUTPUT
LOAD CURRENT STEPPED FROM 0.85A TO 1.7A
(PWM MODE, FIGURE 3 CIRCUIT)
VOUT (AC)
VOUT (AC)
100mV/div
100mV/div
10V/div
ILX
IOUT
200mA/div
1A/div
1A/div
ILX
MODE = SGND
1μs/div
MODE = SGND
40μs/div
MAX17505 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 0.85A TO 1.7A
(PWM MODE, FIGURE 4 CIRCUIT)
40μS/div
MAX17505S 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 0.85A TO 1.7A
(PWM MODE, FIGURE 6 CIRCUIT)
toc23
toc23a
50mV/div
VOUT (AC)
IOUT
VOUT (AC)
50mV/div
1A/div
ILX
1A/div
MODE = SGND
MODE = SGND
100μs/div
40μS/div
MAX17505 5V OUTPUT
LOAD CURRENT STEPPED FROM NO LOAD TO 0.85A
(PWM MODE, FIGURE 3 CIRCUIT)
MAX17505S 5V OUTPUT
LOAD CURRENT STEPPED FROM NO LOAD TO 0.85A
(PWM MODE, FIGURE 5 CIRCUIT)
toc24
toc24a
VOUT (AC)
100mV/div
IOUT
500mA/div
MODE = SGND
40μs/div
www.maximintegrated.com
VOUT (AC)
100mV/div
500mA/div
ILX
MODE = SGND
40μS/div
Maxim Integrated │ 11
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(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.)
MAX17505 3.3V OUTPUT
LOAD CURRENT STEPPED FROM NO LOAD TO 0.85A
(PWM MODE, FIGURE 4 CIRCUIT)
MAX17505S 3.3V OUTPUT
LOAD CURRENT STEPPED FROM NO LOAD TO 0.85A
(PWM MODE, FIGURE 6 CIRCUIT)
toc25a
toc25
VOUT (AC)
50mV/div
500mA/div
IOUT
VOUT (AC)
50mV/div
ILX
MODE = SGND
500mA/div
MODE = SGND
100μs/div
40μS/div
MAX17505 5V OUTPUT
LOAD CURRENT STEPPED FROM 5mA TO 0.85A
(PFM MODE, FIGURE 3 CIRCUIT) toc26
MAX17505S 5V OUTPUT
LOAD CURRENT STEPPED FROM 5MA TO 0.85A
(PFM MODE, FIGURE 5 CIRCUIT)
toc26a
100mV/div
VOUT (AC)
100mV/div
VOUT (AC)
500mA/div
IOUT
ILX
500mA/div
MODE = OPEN
MODE = OPEN
2ms/div
1mS/div
MAX17505 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 5mA TO 0.85A
(PFM MODE, FIGURE 4 CIRCUIT)
toc27
VOUT (AC)
100mV/div
500mA/div
IOUT
toc27a
VOUT (AC)
50mV/div
ILX
500mA/div
MODE = OPEN
2ms/div
www.maximintegrated.com
MAX17505S 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 5mA TO 0.85A
(PFM MODE, FIGURE 6 CIRCUIT)
MODE = OPEN
2mS/div
Maxim Integrated │ 12
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(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.)
MAX17505 5V OUTPUT
LOAD CURRENT STEPPED FROM 50mA TO 0.85A
(DCM MODE, FIGURE 3 CIRCUIT)
toc28
toc28a
100mV/div
VOUT (AC)
500mA/div
IOUT
MAX17505S 5V OUTPUT
LOAD CURRENT STEPPED FROM 50mA TO 0.85A
(DCM MODE, FIGURE 5 CIRCUIT)
VOUT (AC)
100mV/div
IOUT
500mA/div
MODE = VCC
MODE = VCC
200μs/div
200μs/div
MAX17505 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 50mA TO 0.85A
(DCM MODE, FIGURE 4 CIRCUIT)
MAX17505S 3.3V OUTPUT
LOAD CURRENT STEPPED FROM 50mA TO 0.85A
(DCM MODE, FIGURE 6 CIRCUIT)
toc29a
toc29
100mV/div
VOUT (AC)
500mA/div
IOUT
MODE = VCC
VOUT (AC)
100mV/div
500mA/div
IOUT
MODE = VCC
200μs/div
200μs/div
MAX17505 5V OUTPUT
OVERLOAD PROTECTION
(FIGURE 3 CIRCUIT)
MAX17505S 5V OUTPUT
OVERLOAD PROTECTION
(FIGURE 5 CIRCUIT)
toc30
VOUT
toc30a
2V/div
VOUT
IOUT
1A/div
200mV/div
IOUT
1A/div
MODE = VCC
20ms/div
www.maximintegrated.com
MODE = VCC
10ms/div
Maxim Integrated │ 13
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(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.)
MAX17505 5V OUTPUT
APPLICATION OF EXTERNAL CLOCK AT 700kHz
(FIGURE 3 CIRCUIT)
MAX17505S 5V OUTPUT
APPLICATION OF EXTERNAL CLOCK AT 1.2MHz
(FIGURE 5 CIRCUIT)
toc31
VLX
toc31a
10V/div
VLX
VSYNC
2V/div
10V/div
2V/div
VSYNC
MODE = SGND
MODE = SGND
2μs/div
2μs/div
MAX17505S 5V OUTPUT
BODE PLOT
(1.7A LOAD CURRENT, FIGURE 5 CIRCUIT)
MAX17505 5V OUTPUT
BODE PLOT
(1.7A LOAD CURRENT, FIGURE 3 CIRCUIT)
toc32
50
40
PHASE
GAIN (dB)
0
0
-40
-20
-60
CROSSOVER FREQUENCY = 60.7kHz
PHASE MARGIN = 59°
-40
PHASE (°)
40
-10
-30
PHASE
60
GAIN
10
GAIN
CROSSOVER FREQUENCY = 101kHz
PHASE MARGIN = 58.1°
103
FREQUENCY (Hz)
toc33
60
50
PHASE
MAX17505S 3.3V OUTPUT
BODE PLOT
(1.7A LOAD CURRENT, FIGURE 6 CIRCUIT)
30
0
-20
1K
-40
-60
-80
-40
10K
100K
100
PHASE
20
GAIN (dB)
20
CROSSOVER FREQUENCY = 58kHz
PHASE MARGIN = 59°
toc33a
80
40
GAIN
-10
-30
40
100
60
0
-20
120
PHASE (°)
GAIN (dB)
30
10
105
104
FREQUENCY (Hz)
MAX17505 3.3V OUTPUT
BODE PLOT
(1.7A LOAD CURRENT, FIGURE 4 CIRCUIT)
20
-50
-20
100K
40
0
0
-80
-120
10K
50
20
-100
-50
1K
100
40
80
GAIN (dB)
30
20
toc32a
120
100
50
10
GAIN
0
-10
-20
0
CROSSOVER FREQUENCY = 77.7kHz
PHASE MARGIN = 63.2°
-50
-30
103
104
105
FREQUENCY (Hz)
FREQUENCY (Hz)
www.maximintegrated.com
Maxim Integrated │ 14
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
PGND
SGND
VCC
MODE
TOP VIEW
PGND
Pin Configuration
15
14
13
12
11
PGND 16
LX 17
MAX17505/
MAX17505S
LX 18
LX 19
3
VIN
4
5
RESET
2
EN/UVLO
1
VIN
+
VIN
BST 20
10
RT
9
FB
8
CF
7
SS
6
SYNC
TQFN
4mm × 4mm
* EXPOSED PAD (CONNECT TO GROUND).
Pin Description
PIN
NAME
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.
5
RESET
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.
MODE
MODE pin configures 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.
11
www.maximintegrated.com
FUNCTION
Maxim Integrated │ 15
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Pin Description (continued)
PIN
NAME
FUNCTION
12
VCC
13
SGND
5V LDO Output. Bypass VCC with 2.2µF ceramic capacitance to 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
20
BST
—
EP
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.
Boost Flying Capacitor. Connect a 0.1µF ceramic capacitor between BST and LX.
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.
Block Diagram
VCC
MAX17505/MAX17505S
5V
BST
LDO
VIN
SGND
CURRENT-SENSE
LOGIC
EN/UVLO
HICCUP
1.215V
PWM/
PFM/
HICCUP
LOGIC
AND
DRIVERS
LX
RT
PGND
OSCILLATOR
SYNC
CF
FB
VCC
SS
SWITCHOVER
LOGIC
VBG = 0.9V
SLOPE
COMPENSATION
5µA
FB
HICCUP
www.maximintegrated.com
MODE
SELECTION
LOGIC
ERROR AMPLIFIER/
LOOP COMPENSATION
EN/UVLO
MODE
RESET
RESET
LOGIC
Maxim Integrated │ 16
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Detailed Description
The MAX17505/MAX17505S high-efficiency, highvoltage, synchronously 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 highside current-sense amplifier, and a slope-compensation
generator. At each rising edge of the clock, the highside 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.
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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 current at light loads. DCM operation offers efficiency performance 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 RT pin to SGND. The switching frequency (fSW)
is related to the resistor connected at the RT pin (RRT) by
the following equation:
R RT ≅
21× 10 3
− 1.7
f SW
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 1 for RT resistor values
for a few common switching frequencies.
Maxim Integrated │ 17
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Table 1. Switching Frequency vs. RT
Resistor
SWITCHING FREQUENCY (kHz)
500
100
200
400
1000
2200
RT RESISTOR (kΩ)
Open
210
102
49.9
19.1
8.06
Operating Input Voltage Range
The minimum and maximum operating input voltages for
a given output voltage should be calculated as follows:
VIN(MIN) =
VOUT + (I OUT(MAX) × (R DCR + 0.15))
1- (f SW(MAX) × t OFF(MAX) )
+ (I OUT(MAX) × 0.175)
VIN(MAX) =
VOUT
f SW(MAX) × t ON(MIN) )
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
www.maximintegrated.com
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 softstart 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. Highside 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.
Maxim Integrated │ 18
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
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:
=
IRMS I OUT(MAX) ×
VOUT × (VIN - VOUT )
VIN
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:
C IN =
I OUT(MAX) × D × (1- D)
η × f SW × ∆VIN
where D = VOUT/VIN is the duty ratio of the controller,
fSW is 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:
V
L = OUT
f SW
where VOUT, and fSW are nominal values. Select an
inductor whose value is nearest to the value calculated by
the previous formula.
www.maximintegrated.com
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:
C OUT=
1 I STEP × t RESPONSE
×
2
∆VOUT
t RESPONSE ≅ (
0.33
1
)
+
fC
f sw
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 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 fC to 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:
C SS ≥ 28 × 10 -6 × C SEL × VOUT
The soft-start time (tSS) is related to the capacitor
connected at SS (CSS) by the following equation:
C SS
t SS =
5.55 × 10 -6
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-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
VOUT
VIN
R1
R3
EN/UVLO
FB
R2
R4
SGND
SGND
Figure 1. Setting the Input Undervoltage Lockout
Figure 2. Setting the Output Voltage
Setting the Input Undervoltage-Lockout Level
Adjusting Output Voltage
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 3.3MI and then calculate R2 as follows:
R2 =
R1× 1.215
(VINU - 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.
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:
216 × 10 3
R3 =
f C × C OUT
where R3 is in kΩ, crossover frequency fC is 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 fC to be 100kHz.
Table 2. C6 Capacitor Value at Various Switching Frequencies
SWITCHING FREQUENCY RANGE (kHz)
C6 (pF)
200 to 300
2.2
www.maximintegrated.com
300 to 400
1.2
400 to 500
0.75
Maxim Integrated │ 20
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Calculate resistor R4 from the FB pin to SGND as follows
:
R3 × 0.9
R4 =
(VOUT - 0.9)
Power Dissipation
At a particular operating condition, the power losses that
lead to temperature rise of the part are estimated as
follows:
(
1
PLOSS =
(POUT × ( - 1)) - I OUT 2 × R DCR
η
)
P=
OUT VOUT × I OUT
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:
θ JA = 33°C W
θ JC =2°C W
The junction temperature of the device can be estimated
at any given maximum ambient temperature (TA_MAX)
from the equation below:
TJ_MAX
= T A _MAX + (θ JA × PLOSS )
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:
T=
J_MAX TEP_MAX + (θ JC × PLOSS )
www.maximintegrated.com
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-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Recommended Component Placement for MAX17505/MAX17505S
VOUT
PLANE
PGND PLANE
L1
LX PLANE
C1
C4
C5
LX PLANE
PGND PLANE
VIN PLANE
MAX17505/
MAX17505S
SGND
C2
R1
R2
MODE
R6
SYNC
C3
C6
R3
R5
R4
SGND PLANE
www.maximintegrated.com
Maxim Integrated │ 22
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
VIN
(6.5V TO 60V)
C1
2.2µF
VIN
EN/UVLO
RT
VIN
VIN
BST
SYNC
LX
MAX17505
MODE
L1
10µH
VOUT
5V, 1.7A
C4
22µF
LX
R3
178kΩ
LX
VCC
C2
2.2µF
C5
0.1µF
FB
SGND
R4
39kΩ
RESET
CF
SS
PGND
PGND
PGND
C3
5.6nF
fSW = 500kHz
L1 = 10µH (XAL6060-103ME)
C4 = 22µF (MURATA GRM32ER71A226K)
Figure 3. MAX17505 Typical Application Circuit (5V, 500kHz Switching Frequency)
VIN (4.5V TO 60V)
C1
2.2uF
VIN
VIN
EN/UVLO
RT
VIN
VIN
BST
SYNC
LX
MODE
C2
2.2µF
C5
0.1µF
LX
VCC
VOUT
3.3V, 1.7A
C4
47µF
LX
MAX17505
L1
6.8µH
R3
127kΩ
FB
SGND
CF
SS
C3
5600pF
R4
47.5kΩ
RESET
PGND
PGND
PGND
fSW = 500kHz
L1 = 6.8µH (XAL6060-682ME)
C4 = 47µF (MURATA GRM32ER71A476K)
Figure 4. MAX17505 Typical Application Circuit (3.3V, 500kHz Switching Frequency)
www.maximintegrated.com
Maxim Integrated │ 23
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
VIN
C1
2.2µF
R5
EN/UVLO
RT
VIN
VIN
VIN
BST
19.1KΩ
SYNC
C5
0.1µF
L1
4.7µH
LX
C4
10µF
LX
MODE
VOUT
5V,1.7A
MAX17505S
LX
C2
2.2µF
R3
196KΩ
FB
VCC
SGND
R4
43.2KΩ
RESET
CF
SS
PGND
PGND
PGND
C3
5.6nF
fSW = 1MHz
L1 = 4.7µH (XAL4030, 4mm x 4mm)
C4 = 10µH (MURATA GRM32DR71A106KA01)
Figure 5. MAX17505S Typical Application Circuit (5V Output, 1MHz Switching Frequency)
VIN
C1
2.2µF
R5
EN/UVLO
RT
VIN
VIN
VIN
BST
19.1KΩ
SYNC
LX
C5
0.1µF
L1
3.3µH
C4
22µF
LX
MODE
VOUT
3.3V,1.7A
MAX17505S
LX
C2
2.2µF
R3
115KΩ
FB
VCC
SGND
R4
43.2KΩ
RESET
CF
SS
PGND
PGND
PGND
C3
5.6nF
fSW = 1MHz
L1 = 3.3µH (XAL4030, 4mm x 4mm)
C4 = 22µH (MURATA GRM32ER71A226KE20)
Figure 6. MAX17505S Typical Application Circuit (3.3V Output, 1MHz Switching Frequency)
www.maximintegrated.com
Maxim Integrated │ 24
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Ordering Information
PART
MAX17505ATP+
MAX17505SATP+
PIN-PACKAGE
20 TQFN (4mm x 4mm)
20 TQFN-EP* (4mm x 4mm)
Note: Device operates over the -40ºC to +125ºC temperature
range, unless otherwise noted.
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Chip Information
PROCESS: BiCMOS
www.maximintegrated.com
Maxim Integrated │ 25
MAX17505
4.5V-60V, 1.7A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
DESCRIPTION
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
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.
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 specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics 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.
© 2017 Maxim Integrated Products, Inc. │ 26
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