Maxim MAX17761 4.5v to 76v, 1a, high-efficiency, synchronous step-down dc-dc converter Datasheet

MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
General Description
The MAX17761, high-efficiency, high-voltage, synchronous
step-down DC-DC converter with integrated MOSFETs
operates over a 4.5V to 76V input. The converter can
deliver up to 1A current. Output voltage is programmable
from 0.8V up to 90% of VIN. The feedback voltage regulation accuracy over -40°C to +125°C is ±1.5%.
The device features a peak-current-mode control architecture
and can be operated in either the pulse-width modulation
(PWM) or pulse-frequency modulation (PFM) control
schemes.
The MAX17761 is available in a 12-pin (3mm x 3mm)
TDFN package. Simulation models are available.
Applications
●●
●●
●●
●●
●●
●●
Industrial Control Power Supplies
General-Purpose Point-of-Load
Distributed Supply Regulation
Basestation Power Supplies
Wall Transformer Regulation
High-Voltage, Single-Board Systems
Ordering Information appears at end of data sheet.
19-8608; Rev 1; 2/18
Benefits and Features
●● Reduces External Components and Total Cost
• No Schottky—Synchronous Operation
• Internal Compensation Components
• All-Ceramic Capacitors, Compact Layout
●● Reduces Number of DC-DC Regulators to Stock
• Wide 4.5V to 76V Input
• Output Adjustable from 0.8V up to 90% of VIN
• Delivers up to 1A Over Temperature
• 200kHz to 600kHz Adjustable Frequency with
External Clock Synchronization
• Programmable Current Limit
●● Reduces Power Dissipation
• Peak Efficiency > 90%
• PFM Mode Enables Enhanced Light-Load Efficiency
• Auxiliary Bootstrap LDO for Improved Efficiency
• 5μA Shutdown Current
●● Operates Reliably in Adverse Industrial Environments
• Adjustable Soft-Start and Prebiased Power-Up
• Built-in Output-Voltage Monitoring with RESET
• Programmable EN/UVLO Threshold
• Monotonic Startup into Prebiased Load
• Overtemperature Protection
• High Industrial -40°C to +125°C Ambient Operating Temperature Range/-40°C to +150°C Junction
Temperature Range
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Absolute Maximum Ratings
VIN to SGND..........................................................-0.3V to +80V
EN/UVLO to SGND................................................-0.3V to +26V
EXTVCC to SGND.................................................-0.3V to +26V
LX to PGND................................................-0.3V to (VIN + 0.3V)
FB, RESET, SS, MODE/ILIM, VCC,
RT/SYNC to SGND..............................................-0.3V to +6V
PGND to SGND.....................................................-0.3V to +0.3V
LX Total RMS Current.........................................................±1.6A
Continuous Power Dissipation (TA = +70°C)
(derate 24.4mW/°C above +70°C)
(Multilayer board).....................................................1951.2mW
Output Short-Circuit Duration.....................................Continuous
Operating Temperature Range (Note 1)............ -40°C to +125°C
Junction Temperature.......................................................+150°C
Storage Temperature Range............................. -65°C to +150°C
Lead Temperature (soldering, 10s).................................. +300°C
Soldering Temperature (reflow)........................................+260°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these
or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Note 1: Junction temperature greater than +125°C degrades operating lifetimes.
Package Information
PACKAGE TYPE: 12 TDFN
Package Code
TD1233+1C
Outline Number
21-0664
Land Pattern Number
90-0397
THERMAL RESISTANCE, FOUR-LAYER BOARD
Junction to Ambient (θJA)
41°C/W
Junction to Case (θJC)
8.5°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.
Electrical Characteristics
(VIN = 24V, VEN/UVLO = unconnected, RRT = 105kΩ (fSW = 400kHz), LX = unconnected, 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
76
V
10
µA
INPUT SUPPLY (VIN)
Input Voltage Range
Input Shutdown Current
Input Quiescent Current
V­IN
IIN-SH
4.5
VEN = 0V, shutdown mode
IQ_PFM
RILIM = open or 422kΩ
IQ_PWM
RILIM = 243kΩ or 121kΩ
2.5
5
195
µA
3
4
5
mA
ENABLE/UVLO (EN)
EN Threshold
VENR
VEN/UVLO rising
1.19
1.215
1.24
VENF
VEN/UVLO falling
1.09
1.115
1.14
V
2.8
µA
VEN-TRUESD
EN Pullup Current
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IEN
VEN/UVLO falling, true shutdown
VEN/UVLO = 1.215V
0.7
2.2
2.5
Maxim Integrated │ 2
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Electrical Characteristics (continued)
(VIN = 24V, VEN/UVLO = unconnected, RRT = 105kΩ (fSW = 400kHz), LX = unconnected, 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
VCC
6V < VIN < 76V, 0mA < IVCC < 5mA
4.75
5
5.25
V
13
26
52
mA
0.25
V
LDO (VCC)
VCC Output Voltage Range
VCC Current Limit
VCC Dropout
VCC UVLO
IVCC-MAX
VCC = 4.3V, VIN = 12V
VCC-DO
VIN = 4.5V, IVCC = 5mA
VCC-UVR
VCC rising
4.05
4.2
4.35
V
VCC-UVF
VCC falling
3.65
3.8
3.95
V
EXTVCC rising
4.65
4.744
4.85
V
EXT LDO
EXTVCC Switchover Threshold
EXTVCC Switchover Threshold
Hysteresis
EXTVCC Dropout
EXTVCC Current Limit
0.3
EXTVCC-DO
EXTVCC = 4.75V, IVCC = 5mA
IVCC-MAX
VCC = 4.3V, EXTVCC = 5V
High-Side pMOS On-Resistance
RDS-ONH
ILX = 0.3A, sourcing
Low-Side nMOS On-Resistance
RDS-ONL
ILX = 0.3A, sinking
15
V
0.1
V
21
34
mA
0.9
1.8
Ω
0.275
0.55
Ω
+1
µA
POWER MOSFETs
LX Leakage Current
ILX-LKG
VIN = 76V, TA = +25°C,
VLX = (VPGND + 1V) to (VIN - 1V)
-1
SOFT-START
Charging Current
ISS
4.7
5
5.3
µA
FEEDBACK (FB)
FB Regulation Voltage
VFB-REG
RILIM = 243kΩ or 121kΩ
0.788
0.8
0.812
V
FB Regulation Voltage
VFB-REG
RILIM = open or 422kΩ
0.788
0.812
0.824
V
IFB
VFB = 1V, TA = +25°C
-100
+100
nA
RILIM = open or RILIM = 243KΩ
1.41
1.6
1.83
A
RILIM = 121kΩ or RILIM = 422kΩ
0.94
1.14
1.3
A
FB Input Leakage Current
CURRENT LIMIT
Peak Current-Limit Threshold
ISOURCELIMIT
RILIM = open or RILIM = 422kΩ
Negative Current-Limit Threshold
PFM Current Level
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ISINK-LIMIT
IPFM
2.5
mA
RILIM = 243kΩ
0.57
0.65
0.725
A
RILIM = 121kΩ
0.35
0.455
0.56
A
RILIM = open
0.235
0.33
0.44
A
RILIM = 422kΩ
0.125
0.23
0.32
A
Maxim Integrated │ 3
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Electrical Characteristics (continued)
(VIN = 24V, VEN/UVLO = unconnected, RRT = 105kΩ (fSW = 400kHz), LX = unconnected, 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
1
1.22
1.44
V
MODE
MODE PFM Threshold
Rising
Hysteresis
0.19
V
TIMINGS
Minimum On-Time
Maximum Duty Cycle
tON-MIN
45
70
110
ns
DMAX
90
93
97
%
RRT = 210kΩ
180
200
220
kHz
RRT = 140kΩ
270
300
330
kHz
RRT = 105kΩ
360
400
440
kHz
RRT = 69.8KΩ
540
600
660
kHz
200
600
kHz
1.15 ×
fSW
1.4
× fSW
kHz
OSCILLATOR
Switching Frequency
fSW
Switching Frequency Adjustable
Range
SYNC Input Frequency
SYNC Pulse Minimum Off time
SYNC High Threshold
Hysteresis
40
VSYNC-H
1
VSYNC-HYS
Number of SYNC Pulses to Enable
Synchronization
ns
1.22
1.44
V
0.18
V
1
Cycles
RESET
FB Threshold for RESET Rising
VFB-OKR
VFB rising
95
%
FB Threshold for RESET Falling
VFB-OKF
VFB falling
92
%
2.1
ms
RESET Delay After FB Reaches
95% Regulation
RESET Output Level Low
IRESET = 1mA
RESET Output Leakage Current
VFB = 1.063 × VFB-REG, TA = +25°C
0.07
V
1
µA
THERMAL SHUTDOWN
Thermal-Shutdown Threshold
Thermal-Shutdown Hysteresis
Temperature rising
160
°C
20
°C
Note 2: Electrical specifications are production tested at TA = +25°C. Specifications over the entire operating temperature range are
guaranteed by design and characterization.
www.maximintegrated.com
Maxim Integrated │ 4
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics
(VIN = 24V, VSGND = VPGND = 0V, CVIN = 2.2μF, CVCC = 1μF, VEN/UVLO = Open, CSS = 33nF, MODE/ILIM = unconnected, 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.)
EFFICIENCY VS. LOAD CURRENT
(3.3V OUTPUT, FIGURE 5 CIRCUIT)
EFFICIENCY VS. LOAD CURRENT
(5V OUTPUT, FIGURE 4 CIRCUIT)
toc01
100
VIN = 12V
EFFICIENCY (%)
70
VIN = 48V
VIN = 60V
VIN = 76V
VIN = 36V
60
50
80
70
VIN = 60V
50
0.0
0.2
0.4
0.6
0.8
LOAD CURRENT (A)
VIN = 48V
60
VIN = 24V
VIN = 12V
1.0
VIN = 76V
0.0
CONDITIONS: PWM MODE, fSW = 400kHz
VIN = 24V
EFFICIENCY (%)
80
70
VIN = 48V
VIN = 76V
50
30
0.00
0.01
0.10
LOAD CURRENT (A)
VIN = 24V
5.00
4.98
VIN = 12V
0.0
LOAD AND LINE REGULATION
(5V OUTPUT, FIGURE 4 CIRCUIT)
0.2
VIN = 76V
VIN = 48V
5.00
4.90
VIN = 36V
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.10
4.95
0.2
VIN = 76V
CONDITIONS: PFM MODE
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0.4
0.6
0.8
LOAD CURRENT (A)
1.0
VIN = 24V
3.34
1.0
VIN = 48V
VIN = 76V
3.33
3.32
3.31
VIN = 36V
VIN = 60V
3.29
0.0
VIN = 48V
3.4
0.2
0.4
0.6
0.8
LOAD CURRENT (A)
1.0
CONDITIONS: PWM MODE
toc08
SOFT-START/SHUTDOWN FROM EN/UVLO,
(5V OUTPUT, PWM MODE, 1A LOAD CURRENT,
FIGURE 4 CIRCUIT)
toc09
VEN/UVLO
5V/div
VOUT
2V/div
VIN = 76V
3.35
VIN = 12V
3.3
VIN = 60V
0.4
0.6
0.8
LOAD CURRENT (A)
toc06
VIN = 12V
VIN = 60V
3.25
0.0
VIN = 36V
3.5
3.45
VIN = 24V
5.05
VIN = 60V
VIN = 48V
LOAD AND LINE REGULATION
(3.3V OUTPUT, FIGURE 5 CIRCUIT)
VIN = 12V
1.00
3.36
CONDITIONS: PWM MODE
toc07
0.01
0.10
LOAD CURRENT (A)
3.30
CONDITIONS: PFM MODE, fSW = 400kHz
5.15
toc05
4.99
4.96
1.00
5.20
0.00
LOAD AND LINE REGULATION
(3.3V OUTPUT, FIGURE 5 CIRCUIT)
4.97
VIN = 36V
VIN = 60V
3.35
VIN = 60V
40
VIN = 48V
CONDITIONS: PFM MODE, fSW = 400kHz
5.01
60
60
40
1.0
5.02
OUTPUT VOLTAGE (V)
VIN = 12V
VIN = 76V
70
50
0.4
0.6
0.8
LOAD CURRENT (A)
LOAD AND LINE REGULATION
(5V OUTPUT, FIGURE 4 CIRCUIT)
toc04
90
80
CONDITIONS: PWM MODE, fSW = 400kHz
EFFICIENCY VS. LOAD CURRENT
(3.3V OUTPUT, FIGURE 5 CIRCUIT)
100
0.2
VIN = 24V
VIN = 36V
90
OUTPUT VOLTAGE (V)
EFFICIENCY (%)
80
VIN = 12V
VIN = 24V VIN = 36V
90
90
toc03
100
EFFICIENCY (%)
100
EFFICIENCY VS. LOAD CURRENT
(5V OUTPUT, FIGURE 4 CIRCUIT)
toc02
VIN = 24V
0.0
0.2
VIN = 36V
0.4
0.6
0.8
LOAD CURRENT (A)
IOUT
1.0
VRESET
0.5A/div
5V/div
2ms/div
CONDITIONS: PFM MODE
Maxim Integrated │ 5
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
(VIN = 24V, VSGND = VPGND = 0V, CVIN = 2.2μF, CVCC = 1μF, VEN/UVLO = Open, CSS = 33nF, MODE/ILIM = unconnected, 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.)
SOFT-START/SHUTDOWN FROM EN/UVLO,
(3.3V OUTPUT, PWM MODE, 1A LOAD CURRENT,
FIGURE 5 CIRCUIT)
SOFT-START/SHUTDOWN FROM EN/UVLO,
(5V OUTPUT, PFM MODE, 5mA LOAD CURRENT,
FIGURE 4 CIRCUIT)
toc11
toc10
VEN/UVLO
5V/div
VOUT
1V/div
IOUT
0.5A/div
VRESET
5V/div
toc12
VEN/UVLO
5V/div
VOUT
2V/div
VRESET
SOFT-START WITH 2.5V PRE-BIAS,
(5V OUTPUT, PWM MODE, 5mA LOAD CURRENT,
FIGURE 4 CIRCUIT)
VRESET
5V/div
VOUT
1V/div
VRESET
SOFT-START WITH 1.65V PRE-BIAS,
(3.3V OUTPUT, PWM MODE, 5mA LOAD CURRENT,
FIGURE 5 CIRCUIT)
5V/div
2ms/div
STEADY-STATE SWITCHING WAVEFORMS
(5V OUTPUT, FIGURE 4 CIRCUIT)
toc15
toc14
toc13
VOUT
VEN/UVLO
5V/div
2ms/div
2ms/div
VEN/UVLO
SOFT-START/SHUTDOWN FROM EN/UVLO,
(3.3V OUTPUT, PFM MODE, 5mA LOAD CURRENT,
FIGURE 5 CIRCUIT)
5V/div
VEN/UVLO
5V/div
2V/div
VOUT
1V/div
5V/div
VRESET
VOUT
(AC)
20mV/div
VLX
10V/div
ILX
1A/div
5V/div
2ms/div
2ms/div
2µs/div
CONDITIONS: 1A LOAD CURRENT
STEADY-STATE SWITCHING WAVEFORMS
(5V OUTPUT, FIGURE 4 CIRCUIT)
STEADY-STATE SWITCHING WAVEFORMS
(5V OUTPUT, FIGURE 4 CIRCUIT)
toc16
VOUT
(AC)
10mV/div
LOAD CURRENT STEPPED FROM 0.5A TO 0.75A
(5V OUTPUT, PWM MODE, FIGURE 4 CIRCUIT)
toc18
toc17
VOUT
(AC)
50mV/div
VOUT
(AC)
VLX
VLX
100mV/div
10V/div
10V/div
ILX
500mA/div
500mA/div
ILX
IOUT
2µs/div
CONDITIONS: NO LOAD CURRENT
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10μs/div
200mA/div
100µs/div
CONDITIONS: PFM MODE, 25mA LOAD CURRENT
Maxim Integrated │ 6
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
(VIN = 24V, VSGND = VPGND = 0V, CVIN = 2.2μF, CVCC = 1μF, VEN/UVLO = Open, CSS = 33nF, MODE/ILIM = unconnected, 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.)
LOAD CURRENT STEPPED FROM 0.5A TO 0.75A
(3.3V OUTPUT, PWM MODE, FIGURE 5 CIRCUIT)
toc19
toc20
50mV/div
VOUT
(AC)
VOUT
(AC)
IOUT
IOUT
LOAD CURRENT STEPPED FROM 0A TO 0.25A
(3.3V OUTPUT, FIGURE 5 CIRCUIT)
LOAD CURRENT STEPPED FROM 0A TO 0.25A
(5V OUTPUT, FIGURE 4 CIRCUIT)
toc21
100mV/div
VOUT
(AC)
50mV/div
100mA/div
IOUT
100mA/div
200mA/div
100µs/div
LOAD CURRENT STEPPED FROM 0A TO 0.25A
(5V OUTPUT, FIGURE 4 CIRCUIT)
toc22
VOUT
(AC)
100µs/div
CONDITIONS: PWM MODE
LOAD CURRENT STEPPED FROM 0A TO 0.25A
(3.3V OUTPUT, FIGURE 5 CIRCUIT)
APPLICATION OF EXTERNAL CLOCK AT 600kHz
(5V OUTPUT, FIGURE 4 CIRCUIT)
toc23
100mV/div
IOUT
100µs/div
CONDITIONS: PWM MODE
100mA/div
VOUT
(AC)
toc24
100mV/div
100mA/div
IOUT
1ms/div
10V/div
VSYNC
2V/div
1ms/div
CONDITIONS: PFM MODE
4μs/div
CONDITIONS: PFM MODE
BODE PLOT
(5V OUTPUT, FIGURE 4 CIRCUIT)
BODE PLOT
(3.3V OUTPUT, FIGURE 5 CIRCUIT)
toc25
40
toc26
40
10
0
0
-10 CROSSOVER
FREQUENCY = 15.9kHz,
PHASE MARGIN = 70.6°
-20
3
10
104
FREQUENCY (Hz)
CONDITIONS: 1A LOAD CURRENT
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-50
105
GAIN (dB)
50
PHASE (°)
20
30
100
20
50
10
0
PHASE (°)
100
30
GAIN (dB)
VLX
0
CROSSOVER
-10
FREQUENCY = 15.8kHz,
PHASE MARGIN = 69.8°
-50
-20
3
10
104
105
FREQUENCY (Hz)
CONDITIONS: 1A LOAD CURRENT
Maxim Integrated │ 7
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Pin Configuration
TOP VIEW
1
PGND
2
VCC
3
EN/UVLO
4
RESET
5
RT/SYNC
6
+
VIN
MAX17761
EP*
12
LX
11
SGND
10
MODE/ILIM
9
SS
8
FB
7
EXTVCC
TDFN
(3mm x 3mm)
*EP = EXPOSED PAD , CONNECTED TO SGND
Pin Description
PIN
NAME
VIN
1
Power-Supply Input. 4.5V to 76V input supply range. Decouple to PGND with a 2.2μF capacitor;
place the capacitor close to the VIN and PGND pins.
PGND
2
Power Ground Pin of the Converter. Connect externally to the power ground plane. Connect the
SGND and PGND pins together at the ground return path of the VCC bypass capacitor.
VCC
3
5V LDO Output. Bypass VCC with a 1μF ceramic capacitance to SGND.
EN/UVLO
4
Enable/Undervoltage Lockout Pin. Drive EN/UVLO high to enable the output. Connect to the center
of the resistor-divider between VIN and SGND to set the input voltage at which the part turns on.
Leave the pin floating for always on operation.
RESET
5
Open-Drain RESET Output. The RESET output is driven low if FB drops below 92% of its set
value. RESET goes high 2.1ms after FB rises above 95% of its set value.
RT/SYNC
6
Programmable Switching Frequency Input. Connect a resistor from RT/SYNC to SGND to set the
switching frequency of the part between 200kHz and 600kHz. An external clock can be connected
to the RT/SYNC pin to synchronize the part with an external frequency.
EXTVCC
7
External Power Supply Input for the Internal LDO.
FB
8
Feedback Input. Connect FB to the center tap of an external resistor-divider from the output to
SGND to set the output voltage.
SS
9
Soft-Start Input. Connect a capacitor from SS to SGND to set the soft-start time.
MODE/ILIM
10
Connect a resistor from MODE/ILIM to SGND to program the peak current limit and mode of
operation of the part. See the Current Limit and Mode of Operation Selection section for more
details.
SGND
11
Analog Ground.
LX
12
Switching Node. Connect LX pin to the switching-side of the inductor.
EP
—
Exposed Pad. Always connect EP to the SGND pin of the IC. Also, connect EP to a large GND
plane with several thermal vias for best thermal performance. Refer to the MAX17761 EV kit data
sheet for an example of the correct method for EP connection and thermal vias.
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FUNCTION
Maxim Integrated │ 8
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Functional (or Block) Diagram
EXTVCC
VIN
MAX17761
VCC
INTERNAL LDO
REGULATOR
POK
VCC_INT
ENOK
EN/UVLO
PEAK-LIMIT
CHIPEN
CURRENTSENSE LOGIC
1.215V
CS
CURRENTSENSE
AMPLIFIER
PFM
THERMAL
SHUTDOWN
HIGH-SIDE
DRIVER
DH
LX
PFM/PWM
CONTROL LOGIC
CLK
RT/SYNC
OSCILLATOR
LOW-SIDE
DRIVER
DL
SLOPE
GND
MODE/ILIM
MODE SELECT
SINK LIMIT
1.22V
CS
FB
SS
EXTERNAL
SOFT-START
CONTROL
ZX/ILIMN
COMP
SLOPE
NEGATIVE
CURRENT REF
RESET
PWM
ERROR
AMPLIFIER
0.76V
ENOK
RESET
LOGIC
FB
CLK
Detailed Description
The MAX17761 step-down regulator operates from 4.5V
to 76V and delivers up to 1A load current on output.
Feedback voltage regulation accuracy meets ±1.5% over
load, line, and temperature.
The device uses a peak-current-mode control scheme.
An internal transconductance error amplifier generates an
integrated error voltage. The error voltage sets the duty
cycle using a PWM comparator, a high-side current-sense
amplifier, and a slope-compensation generator.
At each rising-edge of the clock, the high-side pMOSFET
turns on and remains on until either the appropriate or
maximum duty cycle is reached, or the peak current limit
is detected.
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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
nMOSFET turns on and remains on until either the next
rising edge of the clock arrives or sink current limit is
detected. The inductor releases the stored energy as its
current ramps down, and provides current to the output.
The internal low RDSON pMOS/nMOS switches ensure
high efficiency at full load.
This device also integrates switching frequency selector
pin, current limit and mode of operation selector pin,
enable/undervoltage lockout (EN/UVLO) pin, programmable
soft-start pin and open-drain RESET signal.
Maxim Integrated │ 9
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Current Limit and Mode of Operation Selection
The following table lists the value of the resistors to program
PWM or PFM modes of operation and 1.6A or 1.14A peak
current limits.
The mode of operation cannot be changed on-the-fly after
power-up.
Table 1. RILIM Resistor vs.
Modes of Operation and Peak Current Limit
RILIM (kΩ)
MODE OF
OPERATION
PEAK CURRENT
LIMIT (A)
OPEN
PFM
1.6
422
PFM
1.14
243
PWM
1.6
121
PWM
1.14
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 the PFM mode 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 every clock cycle until the output rises to 102% of
the nominal voltage. Once the output reaches 102% 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% 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% 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% 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. However, the output-voltage ripple is higher
compared to PWM mode of operation and switching
frequency is not constant at light loads.
Linear Regulator (VCC)
The MAX17761 has two internal low dropout regulators
(LDO), which power VCC. One LDO is powered from input
voltage and the other LDO is powered from the EXTVCC
pin. Only one of the two LDOs is in operation at a time,
depending on the voltage levels present at the EXTVCC pin.
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If EXTVCC is greater than 4.74V (typ), VCC is powered from
the EXTVCC pin. If EXTVCC is lower than 4.44V (typ), VCC
is powered from input voltage. Powering VCC from EXTVCC
increases efficiency particularly at higher input voltages.
Typical VCC output voltage is 5V. Bypass VCC to SGND with
a 1µF cap. Both the LDOs can source up to 13mA.
When VCC falls below its undervoltage lockout (3.8V(typ)),
the internal step-down controller is turned off, and LX switching is disabled. The LX switching is enabled again when the
VCC voltage exceeds 4.2V (typ). The 400mV (typ) hysteresis prevents chattering on power-up/power-down.
When the EXTVCC is connected to the output and the
output is shorted such that inductive ringings cause the
output voltage to become temporarily negative, a R-C
network should be connected between the output and the
EXTVCC pin. A 4.7Ω between the output and the pin and
a 0.1µF from the pin to ground is recommended.
Switching Frequency Selection and External
Frequency synchronization
The RT/SYNC pin programs the switching frequency of
the converter. Connect a resistor from RT/SYNC to SGND
to set the switching frequency of the part at any one of
four discrete frequencies—200kHz, 300kHz, 400kHz, and
600kHz. Table 2 provides resistor values.
The internal oscillator of the device can be synchronized to
an external clock signal on the RT/SYNC pin. The external
synchronization clock frequency must be between 1.15 x
fSW and 1.4 x fSW, where fSW is the frequency programmed
by the resistor connected from the RT/SYNC pin.
Table 2. Switching Frequency vs.
RT Resistor
SWITCHING FREQUENCY
(kHz)
RT/SYNC RESISTOR
VALUE (kΩ)
200
210
300
140
400
105
600
69.8
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(MAX) + R DS−ONL(MAX) ))
D MAX
+ (I OUT(MAX) × (R DS−ONH(MAX) − R DS−ONL(MAX) ))
VIN(MAX) =
VOUT
f SW(MAX) × t ON−MIN(MAX)
Maxim Integrated │ 10
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
where:
VOUT = Steady-state output voltage
IOUT(MAX) = Maximum load current
RDCR(MAX) = Worse-case DC resistance of the inductor
fSW(MAX) = Maximum switching frequency
DMAX(MIN) = Minimum value of the maximum allowable
duty ratio (0.9)
tON-MIN(MAX) = Worst-case minimum switch on-time
(110ns)
RDS-ONL(MAX) and RDS-ONH(MAX) = Worst-case on-time
resistances of low-side and high-side internal MOSFETs,
respectively.
Overcurrent Protection
The device is provided with a robust overcurrent-protection
scheme that protects the device under overload and output
short-circuits conditions. The positive current limit is triggered
when the peak value of the inductor current hits a fixed
threshold (ILIM_P, 1.6A/1.14A, depending on the value
of the resistor connected to the MODE/ILIM pin). At this
point, the high-side switch is turned off and the low-side
switch is turned on. The low-side switch is kept on until the
inductor current discharges below 0.7 x ILIM_P.
While in PWM mode of operation, the negative current
limit is triggered when the valley value of the inductor
current hits a fixed threshold (ILIM_N, -0.65A/-0.455A,
depending on the value of the resistor connected to the
MODE/ILIM pin). At this point, the low-side switch is
turned off and the high-side switch is turned on.
RESET Output
Thermal Shutdown Protection
Thermal shutdown protection limits total power dissipation
in the device. When the junction temperature of the device
exceeds +160°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 20°C. 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 protection in normal operation.
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) for a
single output is defined by the following equation:
=
IRMS I OUT ( MAX ) ×
where, IOUT(MAX) = 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 +10°C
temperature rise at the RMS input current for optimal longterm reliability. Use low-ESR ceramic capacitors with highripple-current capability at the input. X7R capacitors are
recommended in industrial applications for their temperature
stability. Calculate the input capacitance using the following
equation:
The device includes RESET pin to monitor the output voltage.
The open-drain RESET output requires an external pullup
resistor. RESET goes high (high impedance) in 2.1ms after
the output voltage increases above 95% of the nominal voltage. RESET goes low when the output voltage drops to below
92% of the nominal voltage. RESET also goes low during
thermal shutdown.
where,
Prebiased Output
η = The efficiency.
When the device starts into a prebiased output, both the
high-side and 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 first with the high-side
switch. The output voltage is then smoothly ramped up to
the target value in alignment with the internal reference.
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VOUT × ( VIN − VOUT )
VIN
C IN =
I OUT(MAX) × D × (1 − D)
η × f SW × ∆VIN
D = VOUT/VIN is the duty ratio of the controller,
fSW = The switching frequency,
ΔVIN = The allowable input voltage ripple,
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.
Maxim Integrated │ 11
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
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:
For RILIM = OPEN or RILIM = 243kΩ,
2.6 × VOUT
L=
f SW
For RILIM = 121kΩ or RILIM = 422kΩ,
3.7 × VOUT
L=
f SW
where, VOUT and fSW are nominal values. Select an
inductor whose value is nearest to the value calculated by
the previous formula.
Select a low-loss inductor closest to the calculated value
with acceptable dimensions and having the lowest possible
DC resistance. The saturation current rating (ISAT) of the
inductor must be high enough to ensure that saturation
can occur only above the peak current-limit value.
Output Capacitor Selection
X7R ceramic output capacitors are preferred due to their
stability over temperature in Industrial applications. The
output capacitor is sized to support a step load of 25%
of the maximum output current in the application, such
that the output voltage deviation is contained to 3% of the
output voltage change. The output capacitance can be
calculated as follows:
1 I STEP × t RESPONSE
C OUT=
×
2
∆VOUT
t RESPONSE ≅
0.33
fC
where,
ISTEP = The load-current step,
tRESPONSE = The response time of the controller,
ΔVOUT = The allowable output-voltage deviation,
fC = The target closed-loop crossover frequency (fC is
chosen to be 15kHz or 1/20th of fSW, whichever is lower),
fSW = The switching frequency.
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.
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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 for the corresponding
output voltage. The selected output capacitance (CSEL) and
the output voltage (VOUT) determine the minimum required
soft-start capacitor as follows:
C SS ≥ 30 × 10 −6 × C SEL × VOUT
The soft-start time (tSS) is related to the capacitor connected
at SS (CSS) by the following equation:
t SS =
C SS
6.25 × 10 −6
For example, to program a 5.3ms soft-start time, a 33nF
capacitor should be connected from the SS pin to SGND.
The minmum possible soft-start time is 5ms.
Adjusting Output Voltage
Set the output voltage with resistive voltage-dividers connected
from the positive terminal of the output capacitor (VOUT)
to SGND (Figure 1). Connect the centre node of the
divider to the FB pin. To optimize efficiency and output
accuracy, use the following calculations to choose the
resistive divider values:
R4 =
15 × VOUT
0.8
R 4 × 0.8
R5 =
( VOUT − 0.8 )
where R4 and R5 are in kΩ.
VOUT
R4
FB
R5
SGND
Figure 1. Adjusting Output Voltage
Maxim Integrated │ 12
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Setting the Undervoltage Lockout Level
Drive EN/UVLO high to enable the output. Leave the pin
floating for always on operation. Set the voltage at which
each converter turns on with a resistive voltage-divider
connected from VIN to SGND (see Figure 2). Connect the
center node of the divider to EN/UVLO pin.
At a particular operating condition, the power losses that
lead to temperature rise of the device are estimated as
follows:
OUT
Choose R1 as follows:
R1 ≤ (110000 x VINU)
where VINU is the input voltage at which the MAX17761
is required to turn on and R1 is in Ω. Calculate the value
of R2 as follows:
R2 =
1.215 × R1
(VINU − 1.215 + (2.5µA × R1))
Series R-C Selection Across
Bottom Feedback Resistor
In order to achieve the targeted bandwidth, R-C series circuit
is connected across bottom feedback resistor (Figure 3).
Selection procedure for series R-C (R6 and C6) values
are as follows:
=
R6
R4 ×R5
k
×
R 4 + R 5 1 − 0.99k
1.125 × 10 6
C6 =
fC ×
k
1− K 2
×R6
(
1
− 1)) − I OUT 2 × R DCR
η
P=
OUT VOUT × I OUT
PLOSS
= (P
×(
)
where,
POUT = The output power,
η = The efficiency of the device
RDCR = The DC resistance of the output inductor (see the
Typical Operating Characteristics for more information on
efficiency at typical operating conditions).
For a typical multilayer board, the thermal performance
metrics for the 12-pin TDFN package are given as:
θJA = 41°C/W
θJC = 8.5°C/W
The junction temperature of the device can be estimated
at any given maximum ambient temperature (TA_MAX)
from the following equation:
TJ_MAX = TA_MAX + (θJA x 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
as:
TJ_MAX = TEP_MAX + (θJC x PLOSS)
where,
k=
 R 4
f C × C OUT × 1 +

 R5
Junction temperatures greater than +125°C degrade
operating lifetimes.
3.6274 × 10 6
COUT = The actual derated capacitance value for a given
bias voltage of selected output capacitor in μF,
VIN
R1
fC = The targeted crossover frequency in Hz,
R4 and R5 = The feedback network values in kΩ,
R6 and C6 are in kΩ and nF respectively.
Power Dissipation
The exposed pad of the IC should be properly soldered to
the PCB to ensure good thermal contact.
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EN/UVLO
R2
SGND
Figure 2. Setting the Undervoltage Lockout Level
Maxim Integrated │ 13
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
PCB Layout Guidelines
VOUT
R4
FB
R6
R5
C6
SGND
Figure 3. Setting R-C Series Network
www.maximintegrated.com
Careful PCB layout is critical to achieve low switching
losses and stable operation. For a sample layout that
ensures first-pass success, refer to the MAX17761 evaluation
kit layouts available at www.maximintegrated.com.
Follow these guidelines for good PCB layout:
All connections carrying pulsed currents must be very
short and as wide as possible. The loop area of these
connections must be made very small to reduce stray
inductance and radiated EMI.
A ceramic input filter capacitor should be placed close to
the VIN pin of the device. The bypass capacitor for the
VCC pin should also be placed close to the VCC pin. The
feedback trace should be routed as far as possible from
the inductor.
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
minimum, typically the return terminal of the VCC bypass
capacitor. The ground plane should be kept continuous as
much as possible.
A number of thermal vias that connect to a large ground
plane should be provided under the exposed pad of the
device for efficient heat dissipation.
Maxim Integrated │ 14
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Application Circuits
L1
VIN
LX
VIN
33µH
C1
2.2µF
VCC
C2
1µF
C4
22µF
PGND
EN/UVLO
VOUT
5V, 1A
R4
95.3K
MAX17761
SGND
R6
16.9K
R5
18.2K
MODE/ILIM
FB
RT/SYNC
C6
4.7nF
RESET
EXTVCC
SS
R1
105K
C3
33nF
VOUT
L1 PN - 74404064330
C1 PN - GRM32ER72A225KA35
C4 PN – GRM32ER71A226K
(PFM MODE, 1.6A PEAK CURRENT LIMIT)
fSW = 400kHz
Figure 4. 5V Output Typical Application Circuit (Part is Always On when the EN/UVLO Pin is Unconnected)
L1
VIN
LX
VIN
C1
2.2µF
EN/UVLO
PGND
VCC
MAX17761
C2
1µF
22µH
C4
47µF
R4
57.6K
SGND
MODE/ILIM
FB
RT/SYNC
VOUT
3.3V, 1A
R6
15.4K
R5
18.2K
C6
6.8nF
RESET
R1
105K
SS
C3
33nF
EXTVCC
(PFM MODE, 1.6A PEAK CURRENT LIMIT)
fSW = 400kHz
L1 PN - XAL5050-223ME
C1 PN - GRM32ER72A225KA35
C4 PN – GRM32ER71A476KE15L
Figure 5. 3.3V Output Typical Application Circuit (Part is Always On when the EN/UVLO Pin is Unconnected)
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Maxim Integrated │ 15
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Ordering Information
PART
MAX17761ATC+
PIN-PACKAGE
PIN-PACKAGE
12 TDFN-EP*
3mm x 3mm
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Chip Information
PROCESS: BiCMOS
www.maximintegrated.com
Maxim Integrated │ 16
MAX17761
4.5V to 76V, 1A, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Revision History
REVISION
NUMBER
REVISION
DATE
0
6/17
Initial release
2/18
Updated the General Description, Benefits and Features, Absolute Maximum
Ratings, Typical Operating Characteristics, Operating Input Voltage Range, and SoftStart Capacitor Selection sections. Updated the Electrical Characteristics and Pin
Description tables. Replaced the Functional Diagram and Typical Application Circuits.
1
PAGES
CHANGED
DESCRIPTION
—
1─2,
4─12, 15
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated 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.
© 2018 Maxim Integrated Products, Inc. │ 17