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MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
General Description
The Himalaya series of voltage regulator ICs, power
modules, and chargers enable cooler, smaller, and simpler
power supply solutions. The MAX17503/MAX17503S
high-efficiency, high-voltage, synchronously rectified stepdown converter with dual integrated MOSFETs operates
over a 4.5V to 60V input. It delivers up to 2.5A 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
-40°C to +125°C is ±1.1%. The device is available in a
compact (4mm x 4mm) TQFN-EP 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 MAX17503S 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/input 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 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
19-6669; Rev 4; 4/21
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 2.5A Over Temperature
• 100kHz to 2.2MHz Adjustable Frequency with
External Clock Synchronization
• MAX17503S Allows Higher Frequency of Operation
• Available in a 20-Pin, 4mm x 4mm TQFN-EP Package
● Reduces Power Dissipation
• Peak Efficiency of 94%
• PFM and DCM Modes for High Light-Load Efficiency
• Shutdown Current = 2.8µA (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
• Wide -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.
MAX17503
4.5V-60V, 2.5A, 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
CF, RESET, SS, MODE, SYNC,
RT to SGND......................................................-0.3V to +6.5V
FB to SGND..........................................................-0.3V to +1.5V
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-EP (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; 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 Information
PACKAGE TYPE: 20 TQFN-EP
Package Code
T2044+4C
Outline Number
21-100172
Land Pattern Number
90-0409
THERMAL RESISTANCE, FOUR-LAYER BOARD
Junction to Ambient (θJA)
33°C/W
Junction to Case (θJC)
2°C/W
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.
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.
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
MAX17503
4.5V-60V, 2.5A, 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)
EN/UVLO Threshold
EN/UVLO Input Leakage Current
VENR
VEN/UVLO rising
1.19
1.215
1.26
VENF
VEN/UVLO falling
1.068
1.09
1.131
-50
0
+50
nA
4.75
5
5.25
V
26.5
54
100
mA
IEN
VEN/UVLO = 0V, TA = +25ºC
V
LDO
VCC Output Voltage Range
VCC
VCC Current Limit
IVCC-MAX
VCC Dropout
VCC-DO
6V < VIN < 60V, IVCC = 1mA
1mA ≤ IVCC ≤ 25mA
VCC = 4.3V, VIN = 6V
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
5.3
µA
-40ºC ≤ TA ≤ +125ºC
0.89
0.9
0.91
V
0 < VFB < 1V, TA = +25ºC
-50
+50
nA
VCC UVLO
V
V
POWER MOSFET AND BST DRIVER
SOFT-START (SS)
Charging Current
ISS
FEEDBACK (FB)
FB Regulation Voltage
VFB_REG
FB Input Bias Current
IFB
MODE
VCC 1.6
VM-DCM
MODE = VCC (DCM mode)
VM-PFM
MODE = open (PFM mode)
VM-PWM
MODE = GND (PWM mode)
FB Threshold for Entering
Hibernate Mode
VFB_HBR
VFB rising
100.8
102.3
103.5
%
FB Threshold for Exiting Hibernate
Mode
VFB_HBF
VFB falling
100
101.1
102.3
%
3.2
3.7
4.3
A
3.7
4.3
5
A
-0.16
0
+0.16
MODE Threshold
V
VCC / 2
1.4
PFM/HIBERNATE MODE
CURRENT LIMIT
Peak Current-Limit Threshold
Runaway Current-Limit Threshold
IPEAK-LIMIT
IRUNAWAY-LIMIT
Valley Current-Limit Threshold
ISINK-LIMIT
PFM Current-Limit Threshold
IPFM
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MODE = open/VCC
MODE = GND
MODE = open
-1.8
0.6
0.75
0.9
A
A
Maxim Integrated │ 3
MAX17503
4.5V-60V, 2.5A, 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
UNITS
RT AND SYNC
Switching Frequency
fSW
SYNC Frequency Capture Range
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
SYNC Pulse Width
SYNC Threshold
FB Undervoltage Trip Level to
Cause Hiccup
1.4 x
fSW
50
VIH
VIL
0.8
Hiccup Timeout
0.56
(Note 3)
Minimum On-Time
tON-MIN
Minimum Off-Time
tOFF-MIN
0.58
0.65
32,768
MAX17503
MAX17503S
55
140
LX Dead Time
RESET Output Level Low
IRESET = 10mA
RESET Output Leakage Current
TA = TJ = +25ºC, VRESET = 5.5V
-0.1
V
V
Cycles
135
ns
80
ns
160
ns
5
RESET
kHz
ns
2.1
VFB-HICF
kHz
ns
0.4
V
+0.1
µA
FB Threshold for RESET Assertion
VFB-OKF
VFB falling
90.5
92
94.6
%VFB-
FB Threshold for RESET
Deassertion
VFB-OKR
VFB rising
93.8
95
97.8
%VFB-
RESET Deassertion Delay After FB
Reaches 95% Regulation
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 +25ºC. 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
MAX17503
4.5V-60V, 2.5A, 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 = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
VIN = 36V
VIN = 24V
70
VIN = 48V
VIN = 12V
60
90
EFFICIENCY (%)
80
VIN = 24V
60
VIN = 48V
VIN = 36V
VIN = 12V
80
VIN = 36V
VIN = 24V
70
VIN = 48V
VIN = 12V
60
500
1000
1500
2000
LOAD CURRENT (mA)
50
30
2500
0
500
1000
1500
2000
2500
VIN = 12V
95
VIN = 24V
90
VIN = 48V
VIN = 12V
50
40
80
75
30
65
MODE = SGND
0
500
1000
1500
2000
60
2500
VIN = 36V
1
10
LOAD CURRENT (mA)
30
MODE = OPEN
10
100
1000
2500
LOAD CURRENT (mA)
MAX17503S, 3.3VOUTPUT,
PFM MODE, FIGURE 4d CIRCUIT,
EFFICIENCY vs. LOADCURRENT
80
85
80
75
70
65
VIN = 48V
60
VIN = 36V
MODE = OPEN
55
50
40
90
EFFICIENCY (%)
EFFICIENCY (%)
VIN = 24V
VIN = 24V
VIN = 12V
VIN = 36V
50
1000 2500
100
MAX17503 toc04
VIN = 12V
90
VIN = 48V
60
toc04a
100
95
70
LOAD CURRENT (mA)
MAX17503, 3.3V OUTPUT, PFM MODE, FIGURE 4b
CIRCUIT EFFICIENCY vs. LOAD CURRENT
2500
80
MODE = OPEN
100
2000
90
VIN = 48V
70
1500
MAX17503S, 5VOUTPUT,
PFM MODE, FIGURE 4c CIRCUIT,
EFFICIENCY vs. LOADCURRENT
100
EFFICIENCY (%)
EFFICIENCY (%)
VIN = 36V
85
1000
LOAD CURRENT (mA)
toc03a
toc02a
100
80
VIN = 24V
500
0
MAX17503, 5V OUTPUT, PFM MODE, FIGURE 4a
CIRCUIT EFFICIENCY vs. LOAD CURRENT
90
60
40
LOAD CURRENT (mA)
MAX17503S, 3.3VOUTPUT,
PWM MODE, FIGURE 4d CIRCUIT,
EFFICIENCY vs. LOADCURRENT
70
MODE = SGND
MODE = SGND
MAX17503 toc03
0
100
EFFICIENCY (%)
70
40
MODE = SGND
20
80
90
50
50
40
100
MAX17503 toc02
MAX17503 toc01
90
EFFICIENCY (%)
100
MAX17503, 3.3V OUTPUT, PWM MODE, FIGURE 4b
CIRCUIT EFFICIENCY vs. LOAD CURRENT
toc01a
100
MAX17503S, 5VOUTPUT, PWMMODE,
FIGURE 4c CIRCUIT,
EFFICIENCY vs. LOADCURRENT
EFFICIENCY (%)
MAX17503, 5V OUTPUT, PWM MODE, FIGURE 4a
CIRCUIT EFFICIENCY vs. LOAD CURRENT
1
10
100
LOAD CURRENT (mA)
www.maximintegrated.com
1000 2500
70
VIN = 48V
60
50
VIN = 12V
VIN = 24V
VIN = 36V
40
30
MODE = OPEN
10
100
1000
2500
LOAD CURRENT (mA)
Maxim Integrated │ 5
MAX17503
4.5V-60V, 2.5A, 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 = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503S, 5VOUTPUT,
DCM MODE, FIGURE 4c CIRCUIT,
EFFICIENCY vs. LOADCURRENT
VIN = 48V
VIN = 24V
50
70
60
40
10
100
0
1000 2500
LOAD CURRENT (mA)
VIN = 24V
VIN = 12V
50
10
100
40
5.04
5.03
10
100
4.99
VIN = 48V
4.95
1000
500
0
MAX17503 toc08
3.33
3.32
3.31
3.30
3.29
VIN = 12V VIN = 24V VIN = 36V
VIN = 48V
3.26
3.25
MODE = SGND
0
www.maximintegrated.com
500
1000
1500
2000
LOAD CURRENT (mA)
2500
4.98
4.97
4.96
4.95
VIN = 36V
VIN = 12V
4.94
0
500
1000
1500
2000
2500
LOAD CURRENT (mA)
MAX17503S, 3.3VOUTPUT,
PWM MODE, FIGURE 4d CIRCUIT,
LOAD AND LINE REGULATION
3.50
3.45
3.40
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
3.34
VIN = 24V
toc08a
3.35
VIN = 48V
4.99
4.92
2500
1000
1500
2000
LOAD CURRENT (mA)
1000 2500
4.93
MODE = SGND
MAX17503, 3.3V OUTPUT, PWM MODE, FIGURE 4b
CIRCUIT LOAD AND LINE REGULATION
3.27
5.00
VIN = 12V VIN = 24V VIN = 36V
4.98
100
5.01
5.00
LOAD CURRENT (mA)
3.28
10
MAX17503S, 5VOUTPUT,
PWM MODE, FIGURE 4c CIRCUIT,
LOAD AND LINE REGULATION
5.02
5.01
4.96
MODE = VCC
1
MODE = VCC
1
LOAD CURRENT (mA)
5.02
4.97
30
20
1000
5.05
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
70
60
1
20
toc07a
VIN = 36V
80
VIN = 36V
MAX17503, 5V OUTPUT, PWM MODE, FIGURE 4a
CIRCUIT LOAD AND LINE REGULATION
toc06a
VIN = 48V
90
VIN = 24V
50
LOAD CURRENT (mA)
MAX17503S, 3.3VOUTPUT,
DCM MODE, FIGURE 4d CIRCUIT,
EFFICIENCY vs. LOADCURRENT
100
MODE = VCC
OUTPUT VOLTAGE (V)
1
VIN = 48V
60
30
10
MODE = VCC
70
40
20
VIN = 36V
30
10
VIN = 12V
50
VIN = 12V
80
VIN = 24V
30
40
20
90
VIN = 36V
80
EFFICIENCY (%)
60
100
MAX17503 toc07
EFFICIENCY (%)
70
VIN = 48V
90
EFFICIENCY (%)
VIN = 12V
80
100
MAX17503 toc05
90
toc05a
100
MAX17503, 3.3V OUTPUT, DCM MODE, FIGURE 4b
CIRCUIT EFFICIENCY vs. LOAD CURRENT
MAX17503 toc06
MAX17503 5V OUTPUT, DCM MODE, FIGURE 4a
CIRCUIT EFFICIENCY vs. LOAD CURRENT
VIN = 48V
VIN = 24V
3.35
3.30
3.25
VIN = 12V
VIN = 36V
3.20
3.15
3.10
0
500
1000
1500
2000
2500
LOAD CURRENT (mA)
Maxim Integrated │ 6
MAX17503
4.5V-60V, 2.5A, 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 = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503S, 5VOUTPUT,
PFM MODE, FIGURE 4c CIRCUIT,
LOAD AND LINE REGULATION
MAX17503 toc09
5.1
5.0
4.9
VIN = 36V
4.8
4.7
5
4.95
VIN = 24V
4.9
500
2500
1000
1500
2000
LOAD CURRENT (mA)
0
500
toc10a
3.30
3.20
VIN = 24V
VIN = 36V
3.10
0
500
1000
3.2
1000
1500
1500
2000
2500
LOAD CURRENT (mA)
VIN = 36V
2000
2500
2400
2200
2000
1800
1600
1400
1200
1000
800
600
400
200
0
VOUT
2V/div
IOUT
1A/div
VRESET
5V/div
1ms/div
500
1000
1500
2000
LOAD CURRENT (mA)
2500
SWITCHING FREQUENCY vs.
RT RESISTANCE
0
10 20 30 40 50 60 70 80 90 100
RRT (kΩ)
toc12a
MAX17503 toc12
VEN/UVLO
2V/div
MODE = OPEN
0
MAX17503S, SOFT-START/
SHUTDOWNFROM EN/UVLO, 5V OUTPUT,
2.5A LOADCURRENT, FIGURE 4c CIRCUIT)
MAX17503, SOFT-START/SHUTDOWN FROM EN/UVLO
5V OUTPUT, 2.5A LOAD CURRENT,
FIGURE 4a CIRCUIT
www.maximintegrated.com
VIN = 24V
3.1
3.0
VIN = 12V
3.40
VIN = 48V
3.3
LOAD CURRENT (mA)
VIN = 48V
3.50
OUTPUT VOLTAGE (V)
4.75
MAX17503S, 3.3VOUTPUT,
PFM MODE,FIGURE 4d CIRCUIT,
LOAD AND LINE REGULATION
3.60
3.00
VIN = 36V
3.4
4.8
MODE = OPEN
0
VIN = 12V
4.85
VIN = 48V
4.6
4.5
VIN = 12V
5.1
5.05
VIN = 12V
3.5
VIN = 48V
5.15
MAX17503 toc11
5.2
3.6
OUTPUT VOLTAGE (V)
VIN = 24V
5.2
SWITCHING FREQUENCY (kHz)
5.3
5.25
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.4
toc09a
5.5
MAX17503, 3.3V OUTPUT, PFM MODE, FIGURE 4b
CIRCUIT LOAD AND LINE REGULATION
MAX17503 toc10
MAX17503, 5V OUTPUT, PFM MODE, FIGURE 4a
CIRCUIT LOAD AND LINE REGULATION
VEN/UVLO
5V/div
VOUT
2V/div
IOUT
1A/div
VRESET
5V/div
1ms/div
Maxim Integrated │ 7
MAX17503
4.5V-60V, 2.5A, 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 = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503S, SOFT-START/
SHUTDOWNFROM EN/UVLO, 3.3V OUTPUT,
2.5A LOADCURRENT, FIGURE 4d CIRCUIT)
MAX17503 SOFT-START/SHUTDOWN FROM EN/UVLO
3.3V OUTPUT, 2.5A LOAD CURRENT,
FIGURE 4b CIRCUIT
toc13a
MAX17503 toc13
VEN/UVLO
2V/div
VEN/UVLO
VOUT
2V/div
VOUT
IOUT
1A/div
IOUT
1A/div
VRESET
5V/div
VRESET
5V/div
5V/div
2V/div
1mS/div
1ms/div
MAX17503 SOFT-START/SHUTDOWN FROM EN/UVLO
5V OUTPUT, PFM MODE, 5mA LOAD CURRENT,
FIGURE 4a CIRCUIT
MAX17503S, SOFT-START/SHUTDOWN
FROMEN/UVLO, 5V OUTPUT, PFM MODE 5MA
LOAD CURRENT, FIGURE 4c CIRCUIT)
toc14a
MAX17503 toc14
MODE = OPEN
VEN/UVLO
2V/div
VOUT
1V/div
VRESET
5V/div
5V/div
VEN/UVLO
1V/div
VOUT
VRESET
5V/div
2mS/div
2ms/div
MAX17503 SOFT-START/SHUTDOWN FROM EN/UVLO,
3.3V OUTPUT, PFM MODE, 5mA LOAD
CURRENT, FIGURE 4b CIRCUIT
MAX17503 toc15
MAX17503S, SOFT-START/SHUTDOWN
FROMEN/UVLO, 3.3V OUTPUT,PFMMODE 5MA
LOAD CURRENT, FIGURE 4d CIRCUIT)
toc15a
MODE = OPEN
VEN/UVLO
2V/div
VOUT
1V/div
VRESET
5V/div
2ms/div
www.maximintegrated.com
5/div
VEN/UVLO
VOUT
1V/div
VRESET
5V/div
2mS/div
Maxim Integrated │ 8
MAX17503
4.5V-60V, 2.5A, 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 = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503 5V OUTPUT, PWM MODE
SOFT-START WITH 2.5V PREBIAS,
FIGURE 4a CIRCUIT
MAX17503S, SOFT-START WITH2.5VPREBIAS,
5V OUTPUT, PWM MODE, FIGURE 4c CIRCUIT
toc16a
MAX17503 toc16
MODE = SGND
5V/div
VEN/UVLO
2V/div
VEN/UVLO
2V/div
VOUT
2V/div
VOUT
VRESET
5V/div
VRESET
5V/div
1ms/div
1mS/div
MAX17503 3.3V OUTPUT, PFM MODE
SOFT-START WITH 2.5V PREBIAS,
FIGURE 4b CIRCUIT
MAX17503S, SOFT-START WITH2.5VPREBIAS,
3.3V OUTPUT, PWM MODE, FIGURE 4d CIRCUIT
toc17a
MAX17503 toc17
MODE = OPEN
VEN/UVLO
2V/div
VEN/UVLO
5V/div
1V/div
VOUT
1V/div
VOUT
VRESET
5V/div
VRESET
5V/div
1ms/div
1mS/div
MAX17503 5V OUTPUT, 2.5A LOAD CURRENT
STEADY-STATE SWITCHING WAVEFORMS,
FIGURE 4a CIRCUIT
MAX17503S, STEADY-STATE
SWITCHING WAVEFORMS, 5VOUTPUT,
2.5A LOADCURRENT, FIGURE 4c CIRCUIT
toc18a
MAX17503 toc18
VOUT (AC)
50mV/div
VOUT
(AC)
VLX
10V/div
VLX
10V/div
ILX
2A/div
ILX
1A/div
1µs/div
www.maximintegrated.com
50mV/div
400nS/div
Maxim Integrated │ 9
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX17503 5V OUTPUT, PWM MODE, NO LOAD
STEADY-STATE SWITCHING WAVEFORMS,
FIGURE 4a CIRCUIT
MAX17503S, STEADY-STATE
SWITCHING WAVEFORMS, 5VOUTPUT,
NO LOAD CURRENT, FIGURE 4c CIRCUIT
toc19a
MAX17503 toc19
VOUT (AC)
50mV/div
MODE = SGND
VLX
10V/div
ILX
500mA/div
VOUT
(AC)
50mV/div
VLX
10V/div
ILX
500mA/div
400ns/div
1µs/div
MAX17503 5V OUTPUT, PFM MODE, 25mA LOAD
STEADY-STATE SWITCHING WAVEFORMS,
FIGURE 4a CIRCUIT
MAX17503S, STEADY-STATE
SWITCHING WAVEFORMS, 5VOUTPUT, PFMMODE,
25mA LOAD CURRENT, FIGURE 4c CIRCUIT
toc20a
MAX17503 toc20
VOUT
(AC)
VOUT (AC)
100mV/div
VLX
10V/div
ILX
500mA/div
ILX
MODE = OPEN
MAX17503 toc21
VOUT (AC)
20mV/div
VLX
10V/div
500mA/div
4μs/div
MAX17503 5V OUTPUT, DCM MODE, 25mA LOAD
STEADY-STATE SWITCHING WAVEFORMS,
FIGURE 4a CIRCUIT
MAX17503S, STEADY-STATE
SWITCHING WAVEFORMS, 5VOUTPUT, DCM MODE,
25mA LOAD CURRENT, FIGURE 4c CIRCUIT
toc21a
VOUT
(AC)
20mV/div
VLX
10V/div
ILX
200mA/div
MODE = VCC
1µs/div
www.maximintegrated.com
10V/div
VLX
10µs/div
ILX
200mA/div
100mV/div
1μs/div
Maxim Integrated │ 10
MAX17503
4.5V-60V, 2.5A, 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 = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503 5V OUTPUT, PWM MODE
(LOAD CURRENT STEPPED FROM 1A TO 2A),
FIGURE 4a CIRCUIT
MAX17503S, 5VOUTPUT,
PWM MODE, FIGURE 4c CIRCUIT
(LOAD CURRENT STEPPED FROM 1A TO2A)
toc22a
MAX17503 toc22
MODE = SGND
VOUT (AC)
100mV/div
VOUT
AC
IOUT
1A/div
ILX
100mV/div
1A/div
40µS/div
40µs/div
MAX17503 3.3V OUTPUT, PWM MODE
(LOAD CURRENT STEPPED FROM 1A TO 2A),
FIGURE 4b CIRCUIT
MAX17503S, 3.3VOUTPUT,
PWM MODE, FIGURE 4d CIRCUIT
(LOAD CURRENT STEPPED FROM 1A TO2A)
toc23a
MAX17503 toc23
MODE = SGND
VOUT (AC)
50mV/div
VOUT
AC
IOUT
1A/div
50mV/div
ILX
2A/div
40μS/div
40µs/div
MAX17503 5V OUTPUT, PWM MODE (LOAD CURRENT
STEPPED FROM NO-LOAD TO 1A),
FIGURE 4a CIRCUIT
MAX17503S, 5V OUTPUT,
PWM MODE, FIGURE 4c CIRCUIT
(LOAD CURRENT STEPPED FROM NO LOAD TO 1A)
toc24a
MAX17503 toc24
MODE = SGND
VOUT (AC)
100mV/div
VOUT
AC
IOUT
1A/div
ILX
40µs/div
www.maximintegrated.com
100mV/div
1A/div
40μS/div
Maxim Integrated │ 11
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX17503 3.3V OUTPUT, PWM MODE (LOAD CURRENT
STEPPED FROM NO-LOAD TO 1A),
FIGURE 4b CIRCUIT
MAX17503S, 3.3V OUTPUT,
PWM MODE, FIGURE 4d CIRCUIT
(LOAD CURRENT STEPPED FROM NO LOAD TO 1A)
toc25a
MAX17503 toc25
MODE = SGND
VOUT (AC)
50mV/div
VOUT
AC
IOUT
1A/div
ILX
50mV/div
1A/div
40μS/div
40µs/div
MAX17503 5V OUTPUT, PFM MODE (LOAD CURRENT
STEPPED FROM 5mA TO 1A),
FIGURE 4a CIRCUIT
MAX17503 toc26
MODE = OPEN
VOUT (AC)
100mV/div
IOUT
500mA/div
2ms/div
MAX17503 3.3V OUTPUT, PFM MODE (LOAD CURRENT
STEPPED FROM 5mA TO 1A),
FIGURE 4b CIRCUIT
MAX17503 toc27
MODE = OPEN
VOUT (AC)
50mV/div
IOUT
500mA/div
2ms/div
www.maximintegrated.com
Maxim Integrated │ 12
MAX17503
4.5V-60V, 2.5A, 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 = +25ºC. All voltages are referenced to GND, unless otherwise noted.)
MAX17503 5V OUTPUT, DCM MODE (LOAD CURRENT
STEPPED FROM 50mA TO 1A),
FIGURE 4a CIRCUIT
MAX17503S, 5VOUTPUT, DCM MODE
(LOAD CURRENT STEPPED FROM 50mATO1A)
FIGURE 4c CIRCUIT
toc28a
MAX17503 toc28
MODE = VCC
VOUT (AC)
100mV/div
IOUT
500mA/div
VOUT
(AC)
100mV/div
IOUT
500mA/div
200µs/div
200μs/div
MAX17503 3.3V OUTPUT, DCM MODE (LOAD CURRENT
STEPPED FROM 50mA TO 1A),
FIGURE 4b CIRCUIT
MAX17503S, 3.3VOUTPUT, DCM MODE
(LOAD CURRENT STEPPED FROM 50mATO1A)
FIGURE 4d CIRCUIT
toc29a
MAX17503 toc29
MODE = VCC
VOUT (AC)
100mV/div
IOUT
500mA/div
VOUT
(AC)
100mV/div
IOUT
500mA/div
200μs/div
200µs/div
MAX17503 5V OUTPUT, OVERLOAD PROTECTION,
FIGURE 4a CIRCUIT
MAX17503S, OVERLOADPROTECTION
5V OUTPUT, FIGURE 4c CIRCUIT
MAX17503 toc30
toc30a
VOUT
500mV/div
VOUT
IOUT
1A/div
IOUT
20ms/div
www.maximintegrated.com
200mV/div
1A/div
10ms/div
Maxim Integrated │ 13
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MAX17503S 5V OUTPUT, APPLICATION OF
EXTERNAL CLOCK AT 1.2MHz,
FIGURE 4c CIRCUIT
MAX17503 5V OUTPUT, APPLICATION OF
EXTERNAL CLOCK AT 700kHz,
FIGURE 4a CIRCUIT
MAX17503 toc31
VSYNC
toc31a
5V/div
VSYNC
50mV/div
VOUT(AC)
5V/div
50mV/div
VOUT(AC)
VLX
20V/div
VLX
20V/div
ILX
2A/div
ILX
2A/div
4µs/div
2µs/div
MAX17503 5V OUTPUT, 2.5A LOAD CURRENT
BODE PLOT, FIGURE 4a CIRCUIT
MAX17503 toc32
50
PHASE
40
80
60
30
40
GAIN
10
20
0
0
-10
-20
CROSSOVER
FREQUENCY = 58.2kHz
-30
PHASE MARGIN = 63.4°
-40
2
1k
4 6 81
2
-20
PHASE (°)
GAIN (dB)
20
-50
100
-40
-60
4 6 81
2
100k
10k
-80
-100
FREQUENCY (Hz)
MAX17503S, 3.3VOUTPUT, 2.5A LOAD CURRENT,
BODE PLOT, FIGURE 4cCIRCUIT
MAX17503 5V OUTPUT, 2.5A LOAD CURRENT
BODE PLOT, FIGURE 4b CIRCUIT
MAX17503 toc33
100
80
30
60
20
40
GAIN
10
20
0
-10
CROSSOVER
FREQUENCY = 62.5kHz
-20
PHASE MARGIN = 61.2°
-30
-40
2
1k
4 6 81
2
0
-20
-40
4 6 81
10k
FREQUENCY (Hz)
www.maximintegrated.com
100k
2
-60
PHASE
GAIN
PHASE (°)
PHASE
40
GAIN (dB)
GAIN (dB)
50
toc33a
120
PHASE (°)
60
CROSSOVER FREQUENCY = 77.5kHz,
PHASE MARGIN = 64.7°
-80
FREQUENCY (Hz)
Maxim Integrated │ 14
MAX17503
4.5V-60V, 2.5A, 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
19
BST
20
EP
+
VIN
1
2
3
4
5
RESET
18
EN/UVLO
LX
MAX17503/
MAX17503S
VIN
17
VIN
LX
10 RT
9
FB
8
CF
7
SS
6
SYNC
TQFN-EP
(4mm x 4mm)
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 MAX17503/
MAX17503S 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
6
SYNC
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 Selection (MODE) section for more details.
11
www.maximintegrated.com
FUNCTION
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.
The device can be synchronized to an external clock using this pin. See the External Clock
Synchronization (SYNC) section for more details.
Maxim Integrated │ 15
MAX17503
4.5V-60V, 2.5A, 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 MAX17503/
MAX17503S 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 MAX17503/
MAX17503S 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 MAX17503/MAX17503S EV
kit data sheets for a layout example.
Block Diagram
VCC
5V
BST
MAX17503/MAX17503S
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
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Detailed Description
The MAX17503/MAX17503S high-efficiency, highvoltage, synchronously rectified step-down converter with
dual integrated MOSFETs operates over a 4.5V to 60V
input. It delivers up to 2.5A 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 DCM control schemes.
The device integrates adjustable-input undervoltage
lockout, adjustable soft-start, open RESET, and external
clock synchronization features. The MAX17503S 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. 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.
www.maximintegrated.com
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 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).
Maxim Integrated │ 17
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
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. To operate the
MAX17503/MAX17503S at switching frequencies lower
than 200kHz, an R-C network has to be connected in
parallel to the resistor connected from RT to SGND, as
shown in Figure 1. The values of the components R8 and
C13 are 90.9kW and 220pF, respectively.
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 MAX17503, 80ns for the MAX17503S).
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
www.maximintegrated.com
External Clock Synchronization (SYNC)
The internal oscillator of the device can be synchronized
to an external clock signal on the SYNC pin. The external
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 3.7A (typ). A runaway current limit on the high-side
switch current at 4.3A (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
R5
R8
C13
Figure 1. Setting the Switching Frequency
Maxim Integrated │ 18
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
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.
temperature stability. Calculate the input capacitance
using the following equation:
Prebiased Output
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.
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 +165°C, 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.
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
www.maximintegrated.com
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.
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:
L=
VOUT
f SW
where VOUT, and fSW are nominal values.
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 3.7A.
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
response time of the controller,
output-voltage deviation, fC is
crossover frequency, and fSW is
step, tRESPONSE is the
DVOUT is the allowable
the target closed-loop
the switching frequency.
Maxim Integrated │ 19
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
VOUT
VIN
R3
R1
FB
EN/UVLO
R2
R4
SGND
SGND
Figure 2. Setting the Input Undervoltage Lockout
Figure 3. Setting the Output Voltage
Table 2. C6 Capacitor Value at Various
Switching Frequencies
For example, to program a 1ms soft-start time, a 5.6nF
capacitor should be connected from the SS pin to SGND.
SWITCHING FREQUENCY RANGE (kHz)
C6 (pF)
200 to 300
2.2
300 to 400
1.2
400 to 500
0.75
For the MAX17503, 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 MAX17503S, 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
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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 3.3MI 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.
If the switching frequency is less than 200kHz, connect
an additional R-C network in parallel to the top resistor of
the feedback divider (R3). See Figure 5 to calculate the
values of the components R7, C12, and C6.
Maxim Integrated │ 20
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
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 3). 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 MAX17503,
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 MAX17503S, 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.
Calculate resistor R4 from the FB pin to SGND as follows:
R4 =
R3 × 0.9
(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
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 )
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 MAX17503 evaluation kit layout available at
www.maximintegrated.com.
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 )
www.maximintegrated.com
Maxim Integrated │ 21
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Recommended Component Placement for MAX17503/MAX17503S
VOUT
PLANE
PGND PLANE
L1
LX PLANE
C1
C4
C5
LX PLANE
PGND PLANE
VIN PLANE
MAX17503/
MAX17503S
SGND
C2
R1
R2
MODE
R6
SYNC
C3
C6
R3
R5
R4
SGND PLANE
www.maximintegrated.com
Maxim Integrated │ 22
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Recommended Component Placement for MAX17503/MAX17503S (continued)
VOUT
PLANE
PGND PLANE
L1
LX PLANE
C1
C4
C5
LX PLANE
PGND PLANE
VIN PLANE
MAX17503/
MAX17503S
SGND
C2
R1
R2
MODE
R6
SYNC
C3
C6
R3
R5
R4
SGND PLANE
www.maximintegrated.com
Maxim Integrated │ 23
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
VIN
(6.5V to 60V)
C1
2.2µF
EN/UVLO
RT
VIN
VIN
VIN
BST
SYNC
C5
0.1µF
LX
VOUT
5V,2.5A
C4
22µF
LX
MAX17503
MODE
L1
10µH
LX
FB
VCC
C2
2.2µF
R3
178kΩ
SGND
R4
39kΩ
RESET
CF
SS
PGND
PGND
PGND
C3
5.6nF
fSW = 500kHz
a) 5V Output, 500kHz Switching Frequency
VIN
(6.5V to 60V)
C1
2.2µF
EN/UVLO
RT
VIN
VIN
VIN
BST
SYNC
LX
LX
MAX17503
MODE
C5
0.1µF
L1
6.8µH
VOUT
3.3V,2.5A
C4
47µF
LX
FB
VCC
C2
2.2µF
R3
127kΩ
SGND
R4
47.5kΩ
RESET
CF
SS
PGND
PGND
PGND
C3
5.6nF
fSW = 500kHz
b) 3.3V Output, 500kHz Switching Frequency
Figure 4. MAX17503/MAX17503S Typical Application Circuits
www.maximintegrated.com
Maxim Integrated │ 24
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
VIN
C1
2.2µF
EN/UVLO
RT
R5
19.1kΩ
VIN
VIN
VIN
BST
SYNC
C5
0.1µF
LX
VOUT
5V,2.5A
C4
10µF
LX
MAX17503S
MODE
L1
4.7µH
LX
FB
VCC
C2
2.2µF
R3
196kΩ
SGND
R4
43.2kΩ
RESET
CF
SS
PGND
PGND
PGND
C3
5.6nF
fSW = 1MHz
L1 = 4.7µH (XAL4030-472ME)
c) 5V Output, 1MHz Switching Frequency
VIN
C1
2.2µF
EN/UVLO
RT
R5
19.1kΩ
VIN
VIN
VIN
BST
SYNC
LX
LX
MAX17503S
MODE
C5
0.1µF
L1
3.3µH
VOUT
3.3V,2.5A
C4
22µF
LX
FB
VCC
C2
2.2µF
R3
115kΩ
SGND
R4
43.2kΩ
RESET
CF
SS
PGND
PGND
PGND
C3
5.6nF
fSW = 1MHz
L1 = 3.3µH (XAL4030-332ME)
d) 3.3V Output, 1MHz Switching Frequency
Figure 4. MAX17503/MAX17503S Typical Application Circuits (continued)
www.maximintegrated.com
Maxim Integrated │ 25
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
VIN
C8
2.2µF
R8
90.9kΩ
C13
220pF
R5
210kΩ
VIN
EN/UVLO
RT
VIN
VIN
SYNC
BST
LX
LX
MAX17503
MODE
C1
2.2µF
C5
L1
0.1µF 33µH
C14
100µF
VOUT
3.3V,2.5A
C4
100µF
C9
100µF
R3
97.6kΩ
LX
C2
2.2µF
VCC
FB
SGND
CF
RESET
SS
PGND
PGND
C6
15pF
R7
1kΩ
C12
47pF
R4
36.5kΩ
PGND
C3
33000pF
fSW = 100kHz
C6 = 1.4x10-6/fSW
C12 = 0.5/(R3 x fSW)
R7 = R3/100
Figure 5. MAX17503/MAX17503S Typical Application Circuit—3.3V Output, 100kHz Switching Frequency
Ordering Information
PART
Chip Information
PIN-PACKAGE
MAX17503ATP+
20 TQFN-EP* (4mm x 4mm)
MAX17503ATP+T
20 TQFN-EP* (4mm x 4mm)
MAX17503SATP+
20 TQFN-EP* (4mm x 4 mm)
MAX17503SATP+T
20 TQFN-EP* (4mm x 4mm)
PROCESS: BiCMOS
Note: All devices operate over the -40ºC to +125ºC temperature range, unless otherwise noted.
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
T = Tape and Reel
www.maximintegrated.com
Maxim Integrated │ 26
MAX17503
4.5V-60V, 2.5A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
With Internal Compensation
Revision History
REVISION
NUMBER
REVISION
DATE
0
8/13
Initial release
1
4/14
Added description and schematic for operation at 100kHz frequency
2
10/16
Added MAX17503S to data sheet, updated junction temperature, and added
TOCs
3
4/17
Updated data sheet title
3.1
4
4/21
PAGES
CHANGED
DESCRIPTION
—
1-9, 12-13, 15, 18
1–17
1–27
Corrected typos
15, 17–18, 21
Updated General Description, Benefits and Features, Package Information,
toc31, toc31a, Pin Configuration, Pin Description, Detailed Description, Figure 4,
Figure 5, and Ordering Information
1, 2, 14, 15,
17, 18, 24, 26
For pricing, delivery, and ordering information, please visit Maxim Integrated’s online storefront at https://www.maximintegrated.com/en/storefront/storefront.html.
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.
© 2021 Maxim Integrated Products, Inc. │ 27
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