MAX17681
General Description
4.5V to 42V Input, High-Efficiency,
Iso-Buck DC-DC Converter
●
Reduces External Components and Total Cost
• No Optocoupler
• Synchronous Primary Operation
• All-Ceramic Capacitors, Compact Layout
●
Reduces Number of DC-DC Regulators to Stock
• Wide 4.5V to 42V Input
• 0.9V to 0.96 x V
IN
Primary Output Voltage
• Delivers Up to 5W Output Power
●
Reduces Power Dissipation
•
Peak Efficiency > 90%
•
0.9μA (typ) Shutdown Current
●
Operates Reliably in Adverse Industrial Environments
• Peak and Sink Current-Limit Protection
• Robust Secondary-Side Output Overcurrent
Protection (MAX17681A)
•
±1.7% Feedback Accuracy
• Programmable EN/UVLO Threshold
• Adjustable Soft-Start
• Overtemperature Protection
• -40°C to +125°C Operation
The MAX17681/MAX17681A is a high-voltage, high-
efficiency, iso-buck DC-DC converter designed to provide
isolated power up to 5W. The device operates over a
wide 4.5V to 42V input and uses primary-side feedback
to regulate the output voltage.
The MAX17681/MAX17681A uses peak-current-mode
control. The low-resistance, on-chip MOSFETs ensure
high efficiency at full load while simplifying the PCB layout.
The MAX17681/MAX17681A devices generate a well
regulated primary side voltage which is then scaled by a
suitable transformer turns ratio to derive isolated secondary
output rails. While both MAX17681 and MAX17681A
support primary side overcurrent protection, the
MAX17681A is an enhanced design that supports robust
secondary-side overcurrent protection as well.
The MAX17681/MAX17681A is available in a compact
10-pin (3mm x 2mm) TDFN package. Simulation models
are available.
Benefits and Features
Applications
●
●
●
●
●
Isolated Fieldbus Interfaces
PLC I/O Modules
Smart Meters
Isolated Power Supplies in Medical Equipment
Floating Power Supply Generation
Ordering Information
appears at end of data sheet.
Application Circuit
V
IN
17V TO 32V
V
IN
EN/UVLO
LX
PGND
T1
1:2.4
D1
V
OUT
24V, 100mA
R4
49.9Ω
Z1
GND
C1
1µF
N
PRI
N
SEC
C7
2.2µF
C3
1µF
V
CC
MAX17681
MAX17681A
SS
FB
R1
105kΩ
R2
10kΩ
C2
10uF
C4
33nF
COMP
R3
4.75kΩ
C5
33nF
RESET
C8
1nF
C6
680pF
19-7053; Rev 2; 1/17
MAX17681
4.5V to 42V Input, High-Efficiency,
Iso-Buck DC-DC Converter
Absolute Maximum Ratings
V
IN
to GND ............................................................-0.3V to +48V
EN/UVLO to GND...................................... -0.3V to (VIN + 0.3V)
LX to PGND............................................... -0.3V to (VIN + 0.3V)
V
CC
, FB,
RESET,
COMP, SS to GND ....................-0.3V to +6V
PGND to GND ......................................................-0.3V to +0.3V
LX Total RMS Current ........................................................±1.6A
Output Short-Circuit Duration ....................................Continuous
Operating Temperature Range ......................... -40°C to +125°C
Junction Temperature ......................................................+150°C
Storage Temperature Range ............................ -65°C to +160°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.
Package Thermal Characteristics
(Note 1)
TDFN
Continuous Power Dissipation (T
A
= +70°C)
(derate 14.9mW/°C above +70°C) (multilayer board)...1188.7mW
Junction-to-Ambient Thermal Resistance (θ
JA
) .......67.3ºC/W
Junction-to-Case Thermal Resistance (θ
JC
) ............18.2ºC/W
Note 1:
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
(V
IN
= 24V, V
GND
= V
PGND
= 0V, C
VIN
= 2.2μF, C
VCC
= 1μF, V
EN
= 1.5V, C
SS
= 3300pF, V
FB
= 0.98 x V
OUT
, COMP = unconnected,
LX = unconnected,
RESET
= unconnected. T
A
= T
J
= -40°C to +125°C, unless otherwise noted. Typical values are at T
A
= +25°C. All
voltages are referenced to GND, unless otherwise noted.) (Note 2)
PARAMETER
INPUT SUPPLY (V
IN
)
Input Voltage Range
Input Supply Current
ENABLE/UVLO (EN/UVLO)
V
ENR
EN Threshold
EN Input Leakage Current
LDO
V
CC
Output Voltage Range
V
CC
Current Limit
V
CC
Dropout
V
CC
UVLO
V
CC
I
VCC-MAX
V
CC-DO
V
CC-UVR
V
CC-UVF
6V < V
IN
< 12V, 0mA < I
VCC
< 10mA,
12V < V
IN
< 42V, 0mA < I
VCC
< 2mA
V
CC
= 4.3V, V
IN
= 12V
V
IN
= 4.5V, I
VCC
= 5mA
V
CC
rising
V
CC
falling
4.65
15
4.1
3.85
3.55
4
3.7
4.15
3.85
5
40
5.35
80
V
mA
V
V
V
ENF
V
EN-TRUESD
I
EN
V
EN
rising
V
EN
falling
V
EN
falling, true shutdown
V
EN
= V
IN
= 42V, T
A
= +25°C
1.183
1.1
1.218
1.135
0.7
8
200
nA
1.253
1.17
V
V
IN
I
IN-SH
I
IN-SW
V
EN
= 0V, shutdown mode
Normal switching mode, no load
4.5
0.9
1.95
42
3.5
2.8
V
µA
mA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
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Maxim Integrated
│
2
MAX17681
4.5V to 42V Input, High-Efficiency,
Iso-Buck DC-DC Converter
Electrical Characteristics (continued)
(V
IN
= 24V, V
GND
= V
PGND
= 0V, C
VIN
= 2.2μF, C
VCC
= 1μF, V
EN
= 1.5V, C
SS
= 3300pF, V
FB
= 0.98 x V
OUT
, COMP = unconnected,
LX = unconnected,
RESET
= unconnected. T
A
= T
J
= -40°C to +125°C, unless otherwise noted. Typical values are at T
A
= +25°C. All
voltages are referenced to GND, unless otherwise noted.) (Note 2)
PARAMETER
POWER MOSFETs
High-Side pMOS On-Resistance
R
DS-ONH
I
LX
= 0.5A
(sourcing)
I
LX
= 0.5A
(sinking)
T
A
= +25°C
T
A
= T
J
= +125°C
(Note 3)
T
A
= +25°C
T
A
= T
J
= +125°C
(Note 3)
0.2
0.55
0.85
1.2
0.35
0.47
1
Ω
Ω
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Low-Side nMOS On-Resistance
R
DS-ONL
I
LX_LKG
LX Leakage Current
SOFT-START (SS)
Charging Current
FEEDBACK (FB)
FB Regulation Voltage
FB Input Bias Current
Transconductance
COMP Source Current
COMP Sink Current
Current Sense Transresistance
CURRENT LIMIT
Peak Current-Limit Threshold
Runaway Current-Limit
Threshold
Sink Current-Limit Threshold
TIMINGS
Switching Frequency
Events to Hiccup After Crossing
Runaway Current Limit
V
OUT
Undervoltage Trip Level
to Cause Hiccup
Hiccup Timeout
Minimum On-Time
Maximum Duty Cycle
LX Dead Time
V
EN
= 0V, T
A
= +25°C, V
LX
= (V
PGND
+ 1V) to (V
IN
– 1V)
V
SS
= 0.5V
4.7
0.884
T
A
= +25°C
I
COMP
= ±2.5μA
510
19
19
0.45
1.4
1.45
1.05
186
590
32
32
0.5
1.65
1.7
1.25
200
1
5
0.9
μA
I
SS
V
FB_REG
I
FB
GM
I
COMP_SRC
I
COMP_SINK
R
CS
I
PEAK-LIMIT
I
RUNAWAY-
LIMIT
5.3
0.916
100
650
55
55
0.55
1.9
2
1.45
213
μA
V
nA
μS
μA
μA
V/A
A
A
A
kHz
TRANSCONDUCTANCE AMPLIFIER (COMP)
I
SINK-LIMIT
f
SW
V
OUT-HICF
V
SS
> 0.95V (soft-start is done)
67.86
70.5
32768
73.14
%
Cycles
t
ON_MIN
D
MAX
V
FB
= 0.98 x V
FB-REG
200
96.5
300
97.5
12
415
98.5
ns
%
ns
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Maxim Integrated
│
3
MAX17681
4.5V to 42V Input, High-Efficiency,
Iso-Buck DC-DC Converter
Electrical Characteristics (continued)
(V
IN
= 24V, V
GND
= V
PGND
= 0V, C
VIN
= 2.2μF, C
VCC
= 1μF, V
EN
= 1.5V, C
SS
= 3300pF, V
FB
= 0.98 x V
OUT
, COMP = unconnected,
LX = unconnected,
RESET
= unconnected. T
A
= T
J
= -40°C to +125°C, unless otherwise noted. Typical values are at T
A
= +25°C. All
voltages are referenced to GND, unless otherwise noted.) (Note 2)
RESET
PARAMETER
SYMBOL
CONDITIONS
I
RESET
= 1mA
V
FB
= 1.01 x V
FB-REG
,
T
A
= 25°C
V
FB-OKF
V
FB-OKR
V
FB
falling
V
FB
rising
V
FB
rising
90.5
93.5
92.5
95.5
1024
MIN
TYP
MAX
0.02
0.45
94.5
97.5
UNITS
V
μA
%
%
Cycles
RESET
Output Level Low
RESET
Output Leakage Current
High
FB Threshold for
RESET
Falling
FB Threshold for
RESET
Rising
RESET
Delay After FB Reaches
95% Regulation
THERMAL SHUTDOWN
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
Temperature rising
165
10
°C
°C
Note 2:
All limits are 100% tested at +25°C. Limits over temperature are guaranteed by design.
Note 3:
Guaranteed by design, not production tested.
www.maximintegrated.com
Maxim Integrated
│
4
MAX17681
4.5V to 42V Input, High-Efficiency,
Iso-Buck DC-DC Converter
Typical Operating Characteristics
(V
IN
= 24V, V
GND
= V
PGND
= 0V, C
VIN
= 1μF, C
VCC
= 1μF, V
EN
= 1.5V, C
SS
= 33nF, V
FB
= 0.98 x V
PRI
, T
A
= +25°C, unless otherwise
noted.)
8
6
4
OUTPUT VOLTAGE REGULATION
toc2
REGULATION (%)
2
0
-2
-4
-6
0
V
IN
= 17V
V
IN
= 32V
V
IN
= 24V
V
IN
= 19V
FIGURE 9
APPLICATION CIRCUIT
10 20 30 40 50 60 70 80 90 100
LOAD CURRENT (mA)
1.26
EN/UVLO THRESHOLD VOLTAGE
VS.
TEMPERATURE
toc4
EN/UVLO THRESHOLD VOLTAGE (V)
1.22
RISING
1.18
1.14
FALLING
1.1
-40
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
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Maxim Integrated
│
5
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