Maxim MAX17531 Reduces power dissipation Datasheet

MAX17531
42V, 50mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
General Description
Features and Benefits
The MAX17531 uses peak-current-mode control and can
be operated in pulse-width modulation (PWM) or pulsefrequency modulation (PFM) modes.
●● Reduces Number of DC-DC Regulators to Stock
• Wide 4V to 42V Input
• Adjustable 0.8V to 0.9 x VIN Output
• 100kHz to 2.2MHz Adjustable Switching Frequency
with External Synchronization
The
MAX17531
high-efficiency,
high-voltage,
synchronous step-down DC-DC converter with integrated
MOSFETs operates over a 4V to 42V input. The converter
can deliver up to 50mA and generates output voltages
from 0.8V up to 0.9 x VIN. The feedback (FB) voltage is
accurate to within ±1.75% over -40°C to +125°C.
●● Reduces External Components and Total Cost
• No Schottky–Synchronous
• Internal Compensation for Any Output Voltage
• Built-In Soft-Start
• All-Ceramic Capacitors, Compact Layout
The device is available in 10-pin (3mm x 2mm) TDFN
and 10-pin (3mm x 3mm) μMAX® packages. Simulation
models are available.
●● Reduces Power Dissipation
• 22µA Quiescent Current
• Peak Efficiency > 90%
• PFM Enables Enhanced Light-Load Efficiency
• 1.2µA Shutdown Current
Applications
●●
●●
●●
●●
Industrial Sensors and Process Control
High-Voltage LDO Replacement
Battery-Powered Equipment
HVAC and Building Control
●● Operates Reliably in Adverse Environments
• Peak Current Limit Protection
• Built-In Output Voltage Monitoring RESET
• Programmable EN/UVLO Threshold
• Monotonic Startup into Prebiased Load
• Overtemperature Protection
• -40°C to +125°C Operation
µMAX is a registered trademark of Maxim Integrated Products, Inc.
Ordering Information appears at end of data sheet.
Typical Application Circuit—High-Efficiency 5V, 50mA Regulator
VIN
6V TO 42V
CIN
1µF
IN
MAX17531
EN/UVLO
LX
GND
SS
VOUT
MODE
FB
RT/SYNC
R3
140kΩ
19-7423; Rev 0; 11/14
L1
330µH
VOUT
5V
COUT
10µF
R4
22.1Ω
C1
0.22µF
R1
261kΩ
R2
49.9kΩ
RESET
L1 COILCRAFT LPS5030-334M
COUT MURATA 10µF/X7R/6.3V/0805 (GRM21BR70J106K)
CIN MURATA 1µF/X7R/50V/1206 (GRM31MR71H105K)
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Absolute Maximum Ratings
IN, EN/UVLO, VOUT, RESET to GND.....................-0.3V to 48V
LX to GND....................................................... -0.3V to IN + 0.3V
RT/SYNC, SS, FB, MODE to GND............................-0.3V to 6V
LX Total RMS Current.........................................................±0.8A
Output Short-Circuit Duration.....................................Continuous
Continuous Power Dissipation (TA = +70°C)
TDFN (derate 14.9mW/°C above +70°C) ............... 1188.7mW
µMAX (derate 8.8mW/°C above +70°C)...................707.3mW
Operating Temperature Range.......................... -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.
Package Thermal Characteristics (Note 1)
TDFN
Junction-to-Ambient Thermal Resistance (θJA)........67.3°C/W
Junction-to-Case Thermal Resistance (θJC).............18.2°C/W
μMAX
Junction-to-Ambient Thermal Resistance (θJA)......113.1°C/W
Junction-to-Case Thermal Resistance (θJC)................42°C/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
(VIN = 24V, VGND = 0V, VOUT = 3.3V, VFB = 0.85V, VEN/UVLO = 1.5V, RT/SYNC = 191kΩ, LX = SS = MODE = RESET = unconnected;
TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to GND, unless
otherwise noted.) (Note 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
42
V
INPUT SUPPLY (IN)
Input Voltage Range
Input Shutdown Current
Input Supply Current
VIN
4
IIN-SH
VEN/UVLO = 0V, TA = +25°C
IQ-PFM
VMODE = unconnected (Note 2)
IQ-PWM
Normal switching mode, VIN = 24V
0.67
1.2
2.25
18
32
180
485
650
2.96
3.05
3.12
µA
EXTERNAL BIAS (VOUT)
VOUT Switchover Threshold
V
ENABLE/UVLO (EN/UVLO)
EN/UVLO Threshold
VENR
VEN/UVLO rising
1.2
1.25
1.3
VENF
VEN/UVLO falling
1.1
1.15
1.2
V
+100
nA
VEN-TRUESD
EN/UVLO Leakage Current
IEN
VEN/UVLO falling, true shutdown
VEN/UVLO = 1.3V, TA = +25°C
0.7
-100
POWER MOSFETs
High-Side pMOS On-Resistance
RDS-ONH
ILX = 0.1A (sourcing)
2.7
5.0
9.5
Ω
Low-Side nMOS On-Resistance
RDS-ONL
ILX = 0.1A (sinking)
1.25
2.5
5
Ω
+1
µA
LX Leakage Current
www.maximintegrated.com
ILX-LKG
VEN = 0V, TA = +25°C,
VLX = (VGND + 1V) to (VIN - 1V)
-1
Maxim Integrated │ 2
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Electrical Characteristics (continued)
(VIN = 24V, VGND = 0V, VOUT = 3.3V, VFB = 0.85V, VEN/UVLO = 1.5V, RT/SYNC = 191kΩ, LX = SS = MODE = RESET = unconnected;
TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to GND, unless
otherwise noted.) (Note 3)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SOFT-START (SS)
Soft-Start Time
tSS
SS = unconnected
4.4
5.1
5.8
ms
SS Charging Current
ISS
VSS = 0.4V
4.7
5
5.3
µA
MODE = GND
0.786
0.8
MODE = unconnected
0.786
0.812
VFB = 1V, TA = 25°C
-100
FEEDBACK (FB)
FB Regulation Voltage
FB Input Leakage Current
VFB-REG
IFB
0.814
0.826
V
+100
nA
110
123
mA
50
66
CURRENT LIMIT
Peak Current-Limit Threshold
IPEAK-LIMIT
Negative Current-Limit
Threshold
ISINK-LIMIT
PFM Current Level
IPFM
97
VMODE = GND
33
VMODE = unconnected
0.01
mA
VMODE = unconnected
28
39
47
mA
RRT = 422kΩ
90
100
111
RRT = 191kΩ
205
220
235
RRT = 130kΩ
295
319
340
RRT = 69.8kΩ
540
592
638
RRT = 45.3kΩ
813
900
973
RRT = 19.1kΩ
1.86
2.08
2.3
MHz
See the Switching Frequency
(RT/ SYNC) section for details
100
2200
kHz
1.1 x fSW
2200
kHz
OSCILLATOR (RT/SYNC)
Switching Frequency
fSW
Switching Frequency
Adjustable Range
SYNC Input Frequency
SYNC Pulse Minimum Off-Time
SYNC Rising Threshold
Hysteresis
40
ns
VSYNC-H
1
1.22
1.44
VSYNC-HYS
0.115
0.18
0.265
Number of SYNC Pulses to
Enable Synchronization
kHz
1
V
Cycles
TIMING
Minimum On-Time
Maximum Duty Cycle
Hiccup Timeout
www.maximintegrated.com
tON-MIN
DMAX
46
82
128
fSW ≤ 600kHz,
VFB = 0.98 x VFB-REG
90
94
98
fSW > 600kHz,
VFB = 0.98 x VFB-REG
87
92
ns
%
51
ms
Maxim Integrated │ 3
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Electrical Characteristics (continued)
(VIN = 24V, VGND = 0V, VOUT = 3.3V, VFB = 0.85V, VEN/UVLO = 1.5V, RT/SYNC = 191kΩ, LX = SS = MODE = RESET = unconnected;
TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. All voltages are referenced to GND, unless
otherwise noted.) (Note 3)
PARAMETER
SYMBOL
FB Threshold for RESET Rising
VFB-OKR
FB Threshold for RESET Falling
VFB-OKF
RESET
CONDITIONS
MIN
TYP
MAX
UNITS
VFB rising
93
95
97
%
VFB falling
90
92
94
%
RESET Delay after FB Reaches
95% Regulation
RESET Output Level Low
IRESET = 1mA
RESET Output Leakage Current
VFB = 1.01 x VFB-REG, TA = +25°C
2.1
ms
0.23
V
1
µA
1.44
V
MODE
MODE PFM Threshold
VMODE-PFM
MODE Hysteresis
VMODE-HYS
MODE Internal Pullup Resistor
1
1.22
0.19
V
VMODE = unconnected
123
VMODE = GND
1390
Temperature rising
160
°C
20
°C
kΩ
THERMAL SHUTDOWN
Thermal-Shutdown Threshold
Thermal-Shutdown Hysteresis
Note 2: Actual IQ-PFM in the application circuit is higher due to additional current in the output voltage feedback resistor divider.
For example, IQ-PFM (MODE = unconnected) = 26µA for Figure 6, 22µA for Figure 7, and 78µA for Figure 11.
Note 3: Limits are 100% tested at TA = +25°C. Limits over the operating temperature range and relevant supply voltage range are
guaranteed by design and characterization.
www.maximintegrated.com
Maxim Integrated │ 4
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Typical Operating Characteristics
(VIN = 24V, VGND = 0V, VOUT = 3.3V, VEN/UVLO = 1.5V, RT/SYNC = 191kΩ, CIN = 1μF, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs LOAD CURRENT
toc1
80
80
70
70
70
VIN = 12V
50
VIN = 36V
VIN = 24V
40
50
40
FIGURE 6 APPLICATION
CIRCUIT, PFM MODE
VOUT = 5V
VIN = 36V
VIN = 24V
10
0
10
1
VIN = 24V
40
VIN = 36V
30
20
FIGURE 7 APPLICATION
CIRCUIT, PWM MODE
VOUT = 3.3V
10
0
10
20
30
40
5.02
4.99
0
10
20
30
40
VIN = 12V VIN = 24V V = 36V
IN
4.975
40
50
OUTPUT VOLTAGE
vs LOAD CURRENT
toc6
VIN = 36V
3.36
3.34
3.32
50
VIN = 12V, 24V
0
10
20
30
40
50
LOAD CURRENT (mA)
OUTPUT VOLTAGE
vs LOAD CURRENT
toc8
FEEDBACK VOLTAGE
VS TEMPERATURE
820
toc9
FIGURE 7 APPLICATION
CIRCUIT, PWM MODE
3.338
3.336
OUTPUT VOLTAGE (V)
4.979
30
3.38
VIN = 12V
3.34
toc7
FIGURE 6 APPLICATION
CIRCUIT, PWM MODE
4.977
20
LOAD CURRENT (mA)
OUTPUT VOLTAGE
vs LOAD CURRENT
4.981
10
FIGURE 7 APPLICATION
CIRCUIT, PFM MODE
VIN = 36V
VIN = 24V
LOAD CURRENT (mA)
4.983
0
3.4
FIGURE 6
APPLICATION
CIRCUIT, PFM MODE
5.05
4.96
50
toc5
OUTPUT VOLTAGE (V)
VIN = 6V
OUTPUT VOLTAGE (V)
VIN = 12V
FIGURE 6 APPLICATION
CIRCUIT, PWM MODE
VOUT = 5V
OUTPUT VOLTAGE
5.08
50
VIN = 36V
LOAD CURRENT (mA)
vs LOAD CURRENT
80
60
0
10
toc4
90
70
40
LOAD CURRENT (mA)
EFFICIENCY VS LOAD CURRENT
100
50
10
810
3.334
FEEDBACK VOLTAGE (V)
1
VIN = 24V
20
FIGURE 7 APPLICATION
CIRCUIT, PFM MODE
VOUT = 3.3V
toc3
VIN = 12V
60
30
20
LOAD CURRENT (mA)
0
VIN = 12V
30
10
0
60
EFFICIENCY (%)
90
80
60
EFFICIENCY vs LOAD CURRENT
100
90
20
OUTPUT VOLTAGE (V)
toc2
90
30
EFFICIENCY (%)
EFFICIENCY vs LOAD CURRENT
100
EFFICIENCY (%)
EFFICIENCY (%)
100
3.332
3.33
3.328
VIN = 12V
3.326
3.324
VIN = 24V
VIN = 36V
800
790
3.322
4.973
0
10
20
30
LOAD CURRENT (mA)
www.maximintegrated.com
40
50
3.32
0
10
20
30
LOAD CURRENT (mA)
40
50
780
-40
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
Maxim Integrated │ 5
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Typical Operating Characteristics (continued)
(VIN = 24V, VGND = 0V, VOUT = 3.3V, VEN/UVLO = 1.5V, RT/SYNC = 191kΩ, CIN = 1μF, TA = +25°C, unless otherwise noted.)
NO LOAD SUPPLY CURRENT
VS INPUT VOLTAGE
20
6
16
26
1
-0.5
-2
36
SHUTDOWN CURRENT (µA)
40
2.5
6
16
26
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
SWITCH CURRENT LIMIT
VS INPUT VOLTAGE
150
SWITCH CURRENT LIMIT (A)
75
SWITCH NEGATIVE
CURRENT LIMIT
50
25
6
16
1000
26
75
SWITCH NEGATIVE
CURRENT LIMIT
50
25
-40
-20
0
20
40
60
80
100
120
-40
-20
0
20
40
60
80
100
120
EN/UVLO THRESHOLD VOLTAGE
VS TEMPERATURE
1.3
toc15
RISING
1.26
1.22
1.18
FALLING
1.14
1.1
-40
-20
0
20
40
60
80
100
120
TEMPERATURE (°C)
SWITCHING FREQUENCY
VS TEMPERATURE
RESET THRESHOLD
VS TEMPERATURE
LOAD TRANSIENT RESPONSE,
PFM MODE (LOAD CURRENT STEPPED
FROM 2mA to 27mA)
toc16
96
RT = 69.8KΩ
600
400
RT = 191KΩ
200
RISING
0
20
40
60
TEMPERATURE (°C)
www.maximintegrated.com
80
VOUT (AC)
94
100
120
93
FALLING
92
90
100mV/div
FIGURE6
APPLICATION
CIRCUIT
FIGURE
6
VOUT=5V
APPLICATION CIRCUIT
VOUT = 5V
IOUT
91
RT = 422KΩ
toc18
toc17
95
-20
0.8
TEMPERATURE (°C)
RT = 45.3KΩ
-40
1.1
INPUT VOLTAGE (V)
800
0
toc14
100
0
36
RESET THRESHOLD (%)
SWITCH CURRENT LIMIT (A)
100
1.4
TEMPERATURE (°C)
SWITCH PEAK
CURRENT LIMIT
125
toc12
1.7
0.5
36
SWITCH CURRENT LIMIT
VS TEMPERATURE
150
SWITCH PEAK
CURRENT LIMIT
125
SWITCHING FREQUENCY (KHz)
toc13
SHUTDOWN CURRENT
VS TEMPERATURE
2
EN/UVLO THRESHOLD VOLTAGE (V)
PFM MODE
60
0
toc11
4
80
0
SHUTDOWN CURRENT
VS INPUT VOLTAGE
toc10
SHUTDOWN CURRENT (µA)
NO LOAD SUPPLY CURRENT (µA)
100
-40
-20
0
20
40
60
80
100
120
20mA/div
200µs/div
TEMPERATURE (°C)
Maxim Integrated │ 6
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Typical Operating Characteristics (continued)
(VIN = 24V, VGND = 0V, VOUT = 3.3V, VEN/UVLO = 1.5V, RT/SYNC = 191kΩ, CIN = 1μF, TA = +25°C, unless otherwise noted.)
toc19
VOUT (AC)
LOAD TRANSIENT RESPONSE
PFM OR PWM MODE (LOAD CURRENT
STEPPED FROM 25mA TO 50mA)
LOAD TRANSIENT RESPONSE
PFM OR PWM MODE (LOAD CURRENT
STEPPED FROM 25mA TO 50mA)
LOAD TRANSIENT RESPONSE
PFM MODE (LOAD CURRENT STEPPED
FROM 2mA to 27mA)
toc20
50mV/div
toc21
VOUT (AC)
50mV/div
VOUT (AC)
IOUT
20mA/div
IOUT
50mV/div
FIGURE 7
FIGURE7
APPLICATION
CIRCUITCIRCUIT
APPLICATION
VOUT = 3.3V
VOUT=3.3V
IOUT
FIGURE 6
APPLICATION CIRCUIT
VOUT = 5V
20mA/div
200µs/div
20mA/div
FIGURE 7
APPLICATION CIRCUIT
VOUT = 3.3V
100µs/div
100µs/div
LOAD TRANSIENT RESPONSE
PWM MODE (LOAD CURRENT STEPPED
FROM NO LOAD TO 25mA)
LOAD TRANSIENT RESPONSE
PWM MODE (LOAD CURRENT STEPPED
FROM NO LOAD TO 25mA)
SWITCHING WAVEFORMS
(PFM MODE)
toc23
toc22
toc24
FIGURE 6 APPLICATION CIRCUIT
VOUT = 5V, LOAD = 10mA
VOUT(AC)
50mV/div
FIGURE 7
APPLICATION CIRCUIT
VOUT = 3.3V
FIGURE 6
APPLICATION CIRCUIT
VOUT = 5V
IOUT
20mA/div
100mV/div
20mA/div
10V/div
50mA/div
ILX
100µs/div
FULL-LOAD SWITCHING WAVEFORMS
(PWM OR PFM MODE)
10µs/div
NO-LOAD SWITCHING WAVEFORMS
(PWM MODE)
toc25
20mV/div
10V/div
SOFT-START
toc26
FIGURE 6 APPLICATION CIRCUIT
VOUT = 5V
FIGURE 6 APPLICATION CIRCUIT
VOUT = 5V, LOAD = 50mA
LX
VOUT(AC)
LX
IOUT
100µs/div
VOUT(AC)
50mV/div
VOUT(AC)
VOUT(AC)
20mV/div
LX
10V/div
VEN/UVLO
FIGURE 6
APPLICATION
CIRCUIT
VOUT = 5V
toc27
5V/div
2V/div
VOUT
20mA/div
50mA/div
ILX
50mA/div
ILX
4µs/div
www.maximintegrated.com
4µs/div
5V/div
IOUT
VRESET
1ms/div
Maxim Integrated │ 7
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Typical Operating Characteristics (continued)
(VIN = 24V, VGND = 0V, VOUT = 3.3V, VEN/UVLO = 1.5V, RT/SYNC = 191kΩ, CIN = 1μF, TA = +25°C, unless otherwise noted.)
SOFT-START
VEN/UVLO
toc28
SHUTDOWN WITH ENABLE
5V/div VEN/UVLO
5V/div
FIGURE 7
APPLICATION CIRCUIT
VOUT = 3.3V
VOUT
2V/div
20mA/div
VOUT
IOUT
5V/div
VRESET
SOFT-START WITH 3V PREBIAS
toc29
FIGURE 6
APPLICATION CIRCUIT
VOUT = 5V
IOUT
VOUT
5V/div
FIGURE 6
APPLICATION CIRCUIT
NO-LOAD
PWM MODE
5V/div
VRESET
1ms/div
OVERLOAD PROTECTION
toc31
1V/div
5V/div
1V/div
20mA/div
1ms/div
1ms/div
EXTERNAL SYNCHRONIZATION
VEN/UVLO
2V/div
VRESET
toc30
VOUT
toc32
2V/div
VRT/SYNC
10V/div
VLX
20mA/div
ILX
ILX
50mA/div
2µs/div
40us/div
BODE PLOT
toc33
PHASE
FIGURE 6 APPLICATION CIRCUIT
VOUT = 5V
FREQUENCY(Hz)
www.maximintegrated.com
GAIN (dB)
GAIN
PHASE (º)
GAIN (dB)
PHASE
FCR = 16.3KHz,
PHASE MARGIN = 58°
toc34
FCR = 17.3KHz,
PHASE MARGIN = 57°
GAIN
PHASE (º)
BODE PLOT
FIGURE 7 APPLICATION CIRCUIT
VOUT = 3.3V
FREQUENCY(Hz)
GAIN
Maxim Integrated │ 8
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Pin Configurations
TOP VIEW
LX
10
GND MODE RESET VOUT
9
8
7
6
MAX17531
+
1
IN
2
3
4
5
EN/ RT/ SS
UVLO SYNC
FB
IN
1
EN/UVLO
2
RT/SYNC
3
SS
FB
+
MAX17531
10
LX
9
GND
8
MODE
4
7
RESET
5
6
VOUT
µMAX
3mm x 3mm
TDFN
3mm x 2mm
Pin Description
PIN
NAME
1
IN
FUNCTION
2
EN/UVLO
Active-High, Enable/Undervoltage-Detection Input. Pull EN/UVLO to GND to disable the regulator output.
Connect EN/UVLO to IN for always-on operation. Connect a resistor-divider between IN, EN/UVLO, and
GND to program the input voltage at which the device is enabled and turns on.
3
RT/SYNC
Oscillator Timing Resistor Input. Connect a resistor from RT/SYNC to GND to program the switching
frequency from 100kHz to 2.2MHz. See the Switching Frequency (RT/SYNC) section for details. An external
pulse can be applied to RT/SYNC through a coupling capacitor to synchronize the internal clock to the
external pulse frequency. See the External Synchronization section for details.
4
SS
Soft-Start Capacitor Input. Connect a capacitor from SS to GND to set the soft-start time. Leave SS
unconnected for default 5.1ms internal soft-start.
5
FB
Output Feedback Connection. Connect FB to a resistor-divider between VOUT and GND to set the
output voltage. See the Adjusting the Output Voltage section for details.
6
VOUT
External Bias Input for Internal Control Circuitry. Decouple to GND with a 0.22μF capacitor and connect to
output capacitor positive terminal with a 22.1Ω resistor for applications with an output voltage from 3.3V to
5V. Connect to GND for output voltages < 3.3V and > 5V. See the External Bias (VOUT) section for details.
7
RESET
Open-Drain Reset Output. Pull up RESET to an external power supply with an external resistor. RESET
pulls low if FB voltage drops below 92% of its set value. RESET goes high-impedance 2ms after FB voltage
rises above 95% of its set value.
8
MODE
PFM/PWM Mode-Selection Input. Connect MODE to GND to enable the fixed-frequency PWM operation.
Leave MODE unconnected for light-load PFM operation.
9
GND
10
LX
Inductor Connection. Connect LX to the switching-side of the inductor. LX is high-impedance when the
device is in shutdown.
—
EP
Exposed Pad (TDFN Only). Connect to the GND pin to the IC.
Switching Regulator Input. Connect a X7R 1µF ceramic capacitor from IN to GND for bypassing.
Ground. Connect GND to the power ground plane. Connect all the circuit ground connections together at a
single point. See the PCB Layout Guidelines section.
www.maximintegrated.com
Maxim Integrated │ 9
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Block Diagram
IN
INTERNAL
LDO
REGULATOR
VOUT
POK
VCC_INT
PEAK-LIMIT
EN/UVLO
CURRENTSENSE
LOGIC
CHIPEN
1.25V
PFM
THERMAL
SHUTDOWN
CLK
RT/SYNC
PFM/PWM
CONTROL
LOGIC
OSCILLATOR
SLOPE
VCC_INT
SLOPE
SS
CS
INTERNAL OR
EXTERNAL
SOFT-START
CONTROL
DH
LX
LOW-SIDE
DRIVER
MODE SELECT
1.22V
FB
CURRENTSENSE
AMPLIFIER
HIGH-SIDE
DRIVER
DL
MODE
CS
SINK-LIMIT
CURRENT
SENSE
AMPLIFIER
PWM
ERROR
AMPLIFIER
NEGATIVE
CURRENT
REF
GND
RESET
0.76V
FB
CLK
2ms
DELAY
MAX17531
www.maximintegrated.com
Maxim Integrated │ 10
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Detailed Description
The
MAX17531
high-efficiency,
high-voltage,
synchronous step-down DC-DC converter with integrated
MOSFETs operates over a 4V to 42V input voltage range.
The converter can deliver output current up to 50mA at
output voltages of 0.8V to 0.9 x VIN. The output voltage
is accurate to within ±1.75% over -40°C to +125°C. The
converter consumes only 22µA of supply current in PFM
mode, while regulating the output voltage at no load.
The device uses an internally-compensated, peakcurrent-mode-control architecture (see the Block
Diagram). On the rising-edge of the internal clock, the
high-side pMOSFET turns on. An internal error-amplifier
compares the feedback voltage to a fixed internal reference voltage and generates an error voltage. The error
voltage is compared to a sum of the current-sense voltage
and a slope-compensation voltage by a PWM comparator
to set the on-time. During the on-time of the pMOSFET,
the inductor current ramps up. For the remainder of the
switching period (off-time), the pMOSFET is kept off and
the low-side nMOSFET turns on. During the off-time,
the inductor releases the stored energy as the inductor
current ramps down, providing current to the output.
Under overload conditions, the cycle-by-cycle currentlimit feature limits inductor peak current by turning off the
high-side pMOSFET and turning on the low-side nMOSFET.
Mode Selection (MODE)
The device features a MODE pin for selecting either the
forced-PWM or PFM mode of operation. If the MODE pin
is left unconnected, the device operates in PFM mode
at light loads. If the MODE pin is grounded, the device
operates in a constant-frequency forced-PWM mode at all
loads. The mode of operation can be changed on-the-fly
during normal operation of the device.
In PWM mode, the inductor current is allowed to go
negative. PWM operation is useful in frequency-sensitive
applications and provides fixed switching frequency at all
loads. However, the PWM mode of operation gives lower
efficiency at light loads when compared to the PFM mode of
operation.
PFM mode 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 39mA (typ) (IPFM) every clock cycle until the output rises to 102% (typ) of the nominal voltage. Once the
output reaches 102% (typ) of the nominal voltage, both
high-side and low-side FETs are turned off and the device
www.maximintegrated.com
enters hibernate operation until the load discharges the
output to 101% (typ) 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% (typ) 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% (typ) of the
nominal output voltage. The device naturally exits PFM
mode when the load current increases to a magnitude of
approximately:
IPFM - (ΔI/2)
where ΔI is the peak-peak ripple current in the output
inductor. The part enters PFM mode again if the load
current reduces to approximately (ΔI/2). See the Inductor
Selection section for details. The advantage of the PFM
mode is higher efficiency at light loads because of lower
current drawn from the supply.
Enable Input (EN/UVLO) and Soft-Start (SS)
When EN/UVLO voltage increases above 1.25V (typ), the
device initiates a soft-start sequence. The duration of the
soft-start depends on the status of the SS pin voltage at
the time of power-up. If the SS pin is not connected, the
device uses a fixed 5ms internal soft-start to ramp up the
internal error-amplifier reference. If a capacitor is connected from SS to GND, a 5μA current source charges the
capacitor and ramps up the SS pin voltage. The SS pin
voltage is used as reference for the internal error amplifier. Such a reference ramp-up allows the output voltage
to increase monotonically from zero to the final set value
independent of the load current.
EN/UVLO can be used as an input voltage UVLOadjustment input. An external voltage-divider between
IN and EN/UVLO to GND adjusts the input voltage at
which the device turns on or turns off. See Setting the
Input Undervoltage-Lockout Level section for details.
If input UVLO programming is not desired, connect
EN/UVLO to IN (see the Electrical Characteristics table for
EN/UVLO rising and falling-threshold voltages). Driving
EN/UVLO low disables both power MOSFETs, as well as
other internal circuitry, and reduces IN quiescent current
to below 1.2μA. The SS capacitor is discharged with an
internal pulldown resistor when EN/UVLO is low. 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.
Maxim Integrated │ 11
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Switching Frequency (RT/SYNC)
Switching frequency of the device can be programmed
from 100kHz to 2.2MHz by using a resistor connected
from RT/SYNC to GND. The switching frequency (fSW)
is related to the resistor connected at the RT/SYNC pin
(RT) by the following equation, where RT is in kΩ and fSW
is in kHz:
RT =
42000
f SW
The switching frequency in ranges of 130kHz to
160kHz and 230kHz to 280kHz are not allowed for user
programming to ensure proper configuration of the internal
adaptive-loop compensation scheme.
External Synchronization
The RT/SYNC pin can be used to synchronize the
device’s internal oscillator to an external system clock.
The external clock should be coupled to the RT/SYNC
pin through a 47pF capacitor, as shown in Figure 1. The
external clock logic-high level should be higher than
3V, logic-low level lower than 0.5V, and the duty cycle
of the external clock should be in the range of 10% to
70%. External clock-synchronization is allowed only in
PWM mode of operation (MODE pin connected to GND).
The RT resistor should be selected to set the switching
frequency 10% lower than the external clock frequency.
The external clock should be applied at least 500μs after
enabling the device for proper configuration of the internal
loop compensation.
External Bias (VOUT)
The device provides a VOUT pin to power the internal
blocks from a low-voltage supply. When the VOUT pin
MAX17531
47pF
voltage exceeds 3.1V, the device draws switching and
quiescent current from this pin to improve the converter’s
efficiency. In applications with an output voltage setting
from 3.3V to 5V, VOUT should be decoupled to GND
with a ceramic capacitor, and should be connected to the
positive terminal of the output capacitor with a resistor
(R4, C1), as shown in the typical application circuits. In
the absence of R4 and C1, the absolute maximum rating of VOUT (-0.3V) can be exceeded, under short-circuit
conditions, due to oscillations between the ceramic output
capacitor and the inductance of the short-circuit path. In
general, parasitic board or wiring inductance should be
minimized and the output voltage waveform under shortcircuit operation should be verified to ensure that the
absolute maximum rating of VOUT is not exceeded. For
applications with an output voltage setting less than 3.3V
or greater than 5V, VOUT should be connected to GND.
Reset Output (RESET)
The device includes an open-drain RESET output to
monitor output voltage. RESET should be pulled up with
an external resistor to the desired external power supply.
RESET goes high-impedance 2ms after the output rises
above 95% of its nominal set value and pulls low when
the output voltage falls below 92% of the set nominal
output voltage. RESET asserts low during the hiccup
timeout period.
Startup Into a Prebiased Output
The device supports monotonic startup into a prebiased
output. 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.
High-side and low-side switches do not start switching
until the PWM comparator commands the first PWM
pulse, at which point switching commences. The output
voltage is then smoothly ramped up to the target value
in alignment with the internal reference. Such a feature is
useful in applications where digital integrated circuits with
multiple rails are powered.
RT/SYNC
CLOCK
SOURCE
RT
VLOGIC-HIGH
VLOGIC-LOW
DUTY
Figure 1. Synchronization to an External Clock
www.maximintegrated.com
Maxim Integrated │ 12
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Operating Input Voltage Range
The maximum operating input voltage is determined
by the minimum controllable on-time. The minimum
operating input voltage is determined by the maximum
duty cycle and circuit voltage drops. The minimum and
maximum operating input voltages for a given output
voltage should be calculated as follows:
=
VINMIN
VOUT + (I OUT × (R DCR + 5))
+ (I OUT × 4.5)
D MAX
VINMAX =
VOUT
t ONMIN × f SW
where VOUT is the steady-state output voltage, IOUT is
the maximum load current, RDCR is the DC resistance of
the inductor, fSW is the switching frequency (max), DMAX
is the maximum duty cycle (0.9), and tONMIN is the worstcase minimum controllable switch on-time (128ns).
Overcurrent Protection, HICCUP Mode
The device implements a HICCUP-type overload protection scheme to protect the inductor and internal FETs
under output short-circuit conditions. When the inductor
peak current exceeds 0.11A (typ) 16 consecutive times,
the part enters HICCUP mode. In this mode, the part is initially operated with hysteretic cycle-by-cycle peak-current
limit that continues for a time duration equal to twice the
soft-start time. The part is then turned off for a fixed 51ms
hiccup timeout period. This sequence of hysteretic inductor
current waveforms, followed by a hiccup timeout period,
continues until the short/overload on the output is removed.
Since the inductor current is bound between two limits,
inductor-current runway never happens.
Thermal-Overload Protection
Thermal-overload protection limits the total power dissipation in the IC. When the junction temperature exceeds
+160°C, an on-chip thermal sensor shuts down the
device, turns off the internal power MOSFETs, allowing
it to cool down. The device turns on after the junction
temperature cools by 20°C.
www.maximintegrated.com
Applications Information
Inductor Selection
A low-loss inductor having the lowest possible DC
resistance that fits in the allotted dimensions should be
selected. Calculate the required inductance from the
equation:
L=
18000 × VOUT
f SW
where L is inductance in μH, VOUT is output voltage
and fSW is the switching frequency in kHz. Calculate the
peak-peak ripple current (ΔI) in the output inductor from
the equation:


V
1000 × VOUT × 1 − OUT 
V
IN 

∆I =
f SW × L
where L is inductance in μH, VOUT is output voltage, VIN
is input voltage and fSW is the switching frequency in kHz.
The saturation current rating of the inductor must exceed
the maximum current-limit value (IPEAK-LIMIT). The
saturation current rating should be at least 0.123A.
Once the L value is known, the next step is to select
the right core material. Ferrite and powdered iron are
commonly available core materials. Ferrite cores have
low core losses and are preferred for high-efficiency
designs. Powdered iron cores have more core losses and
are relatively cheaper than ferrite cores.
Input Capacitor Selection
Small ceramic input capacitors are recommended for the
IC. The input capacitor reduces peak current drawn from
the power source and reduces noise and voltage ripple
on the input caused by the switching circuitry. A minimum
of 1μF, X7R-grade capacitor in a package larger than 0805
is recommended for the input capacitor of the IC to keep the
input-voltage ripple under 2% of the minimum input voltage,
and to meet the maximum ripple-current requirements.
Maxim Integrated │ 13
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Output Capacitor Selection
Small ceramic X7R-grade output capacitors are recommended for the device. The output capacitor has two
functions. It stores sufficient energy to support the output
voltage under load-transient conditions and stabilizes the
device’s internal control loop. Usually, the output capacitor is sized to support a step load of 50% of the maximum
output current in the application, such that the outputvoltage deviation is less than 3%. The minimum required
output capacitance (COUT) is calculated as:
COUT (in µF) = 25/VOUT
It should be noted that dielectric materials used in ceramic
capacitors exhibit capacitance loss due to DC bias
levels and should be appropriately derated to ensure the
required output capacitance is obtained in the application.
Soft-Start Capacitor Selection
The device offers a 5.1ms internal soft-start when the
SS pin is left unconnected. When adjustable soft-start
time is required, connect a capacitor from SS to GND
to program the soft-start time. The minimum soft-start
time is related to the output capacitance (COUT) and the
output voltage (VOUT) by the following equation.
tSS > 0.05 x COUT x VOUT
where tSS is in milliseconds and COUT is in μF. Soft-start
time (tSS) is related to the capacitor connected at SS
(CSS) by the following equation:
C=
SS 6.25 × t SS
where tSS is in milliseconds and CSS is in nanofarads.
Setting the Input Undervoltage-Lockout Level
The device offers an adjustable input undervoltagelockout level. Set the voltage at which the device turns on
with a resistive voltage-divider connected from IN to GND
(see Figure 2). Connect the center node of the divider to
EN/UVLO.
Choose R1 to be 3.3MΩ max and then calculate R2 as
follows:
R2 =
R1× 1.25
(VINU - 1.25)
where VINU is the voltage at which the device is required
to turn on.
Adjusting the Output Voltage
The output voltage can be programmed from 0.8V to
0.9 x VIN. Set the output voltage by connecting a resistordivider from output to FB to GND (see Figure 3). Choose
R2 in the range of 25kΩ to 100kΩ and calculate R1 with
the following equation:
=
R1
V
R2 ×  OUT
 0.8
−

1

Transient Protection
In applications where fast line transients or oscillations with a slew rate in excess of 15V/µs are expected
during power-up or steady-state operation, the MAX17531
VOUT
VIN
IN
R1
MAX17531
EN/UVLO
MAX17531
R1
FB
R2
R2
GND
Figure 2. Adjustable EN/UVLO Network
www.maximintegrated.com
Figure 3. Setting the Output Voltage
Maxim Integrated │ 14
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
should be protected with a series resistor that forms a
lowpass filter with the input ceramic capacitor (Figure 4).
These transients can occur in conditions such as hotplugging from a low-impedance source or due to inductive
load switching and surges on the supply lines.
Power Dissipation
Ensure that the junction temperature of the device does
not exceed 125°C under the operating conditions specified for the power supply. At a particular operating condition, the power losses that lead to temperature rise of the
device are estimated as follows:

 1 
2
PLOSS =
POUT ×  - 1  - (I OUT × R DCR )
η



particular attention. Follow these guidelines for good PCB
layout:
● Place the input ceramic capacitor as close as possible
to VIN and GND pins
● Minimize the area formed by the LX pin and inductor
connection to reduce the radiated EMI
● Ensure that all feedback connections are short and
direct
● Route high-speed switching node (LX) away from the
signal pins
For a sample PCB layout that ensures the first-pass
success, refer to the MAX17531 evaluation kit data sheet.
P=
OUT VOUT × I OUT
where POUT is the output power, η is the efficiency of
power conversion, and RDCR is the DC resistance of the
output inductor. See the Typical Operating Characteristics
section for the power-conversion efficiency or measure
the efficiency to determine the total power dissipation.
4.7Ω
The junction temperature (TJ) of the device can be
estimated at any ambient temperature (TA) from the
following equation:
IN
CIN
1µF
TJ= T A + (θ JA × PLOSS )
MAX17531
GND
where θJA is the junction-to-ambient thermal impedance
of the package.
PCB Layout Guidelines
Careful PCB layout (Figure 5) is critical to achieve clean
and stable operation. The switching power stage requires
www.maximintegrated.com
Figure 4. Transient Protection
Maxim Integrated │ 15
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
VIN
IN
MAX17531
R1
CIN
R2
L1
LX
VOUT
COUT
EN/UVLO
GND
SS
VOUT
R7
CF
CSS
MODE
R4
FB
VOUT
R5
R6
RT/SYNC
R3
RESET
GND PLANE
CIN
VIN PLANE
R1
R2
R3
U1
LX
IN
COUT
EN/UVLO
GND
RT/SYNC
MODE
RESET
SS
CSS
FB
R4
VOUT
R7
R5
Figure 5. Layout Guidelines
VOUT PLANE
L1
R6
GND PLANE
CF
VIAS TO BOTTOM-SIDE GROUND PLANE
VIAS TO VOUT
www.maximintegrated.com
Maxim Integrated │ 16
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Typical Application Circuits
VIN
6V TO 42V
CIN
1µF
IN
MAX17531
EN/UVLO
L1
330µH
LX
COUT
10µF
GND
MODE
C1
0.22µF
FB
RT/SYNC
R3
140kΩ
IN
CIN
1µF
MAX17531
EN/UVLO
R4
22.1Ω
SS
VOUT
VIN
4V TO 42V
VOUT
5V
SS
LX
GND
VOUT
RT/SYNC
R2
49.9kΩ
VOUT
3.3V
COUT
10µF
MODE
R1
261kΩ
L1
220µH
R4
22.1Ω
C1
0.22µF
R1
158kΩ
FB
R2
49.9kΩ
R3
140kΩ
RESET
RESET
L1 COILCRAFT LPS5030-334M
COUT MURATA 10µF/X7R/6.3V/0805 (GRM21BR70J106K)
CIN MURATA 1µF/X7R/50V/1206 (GRM31MR71H105K)
L1 COILCRAFT LPS5030-224M
COUT MURATA 10µF/X7R/6.3V/0805 (GRM21BR70J106K)
CIN MURATA 1µF/X7R/50V/1206 (GRM31MR71H105K)
Figure 6. High-Efficiency 5V, 50mA Regulator
VIN
6V TO 42V
CIN
1µF
Figure 7. High-Efficiency 3.3V, 50mA Regulator
IN
MAX17531
EN/UVLO
SS
MODE
LX
VOUT
5V
COUT
10µF
GND
VOUT
R4
22.1Ω
C1
0.22µF
R1
261kΩ
FB
R2
49.9kΩ
RT/SYNC
R3
69.8kΩ
L1
150µH
RESET
L1 COILCRAFT LPS3015-154M
COUT MURATA 10µF/X7R/6.3V/0805 (GRM21BR70J106K)
CIN MURATA 1µF/X7R/50V/1206 (GRM31MR71H105K)
Figure 8. Small-Footprint 5V, 50mA Regulator
www.maximintegrated.com
Maxim Integrated │ 17
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Typical Application Circuits (continued)
VIN
4V TO 40V
CIN
1µF
IN
MAX17531
EN/UVLO
SS
MODE
L1
100µH
LX
VIN
4V TO 24V
COUT
10µF
GND
VOUT
IN
CIN
1µF
R4
22.1Ω
MAX17531
EN/UVLO
SS
C1
0.22µF
R1
158kΩ
FB
MODE
R2
49.9kΩ
RT/SYNC
R3
69.8kΩ
VOUT
3.3V
R3
69.8kΩ
GND
VOUT
R1
127kΩ
FB
R2
100kΩ
RESET
L1 COILCRAFT LPS3015-683M
COUT MURATA 10µF/X7R/6.3V/0805 (GRM21BR70J106K)
CIN MURATA 1µF/X7R/50V/1206 (GRM31MR71H105K)
L1 COILCRAFT LPS3015-104M
COUT MURATA 10µF/X7R/6.3V/0805 (GRM21BR70J106K)
CIN MURATA 1µF/X7R/50V/1206 (GRM31MR71H105K)
Figure 9. Small-Footprint 3.3V, 50mA Regulator
CIN
1µF
VOUT
1.8V
COUT
10µF
RT/SYNC
RESET
VIN
15V TO 42V
LX
L1
68µH
Figure 10. Small-Footprint 1.8V, 50mA Regulator
IN
MAX17531
EN/UVLO
SS
MODE
LX
VOUT
12V
COUT
4.7µF
GND
VOUT
R1
348kΩ
FB
R2
24.9kΩ
RT/SYNC
R3
69.8kΩ
L1
470µH
RESET
L1 COILCRAFT LPS4018-474M
COUT MURATA 4.7µF/X7R/16V/0805 (GRM21BR71C475K)
CIN MURATA 1µF/X7R/50V/1206 (GRM31MR71H105K)
Figure 11. Small-Footprint 12V, 50mA Step-Down Regulator
www.maximintegrated.com
Maxim Integrated │ 18
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Package Information
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX17531ATB+
-40°C to +125°C
10 TDFN-EP*
MAX17531AUB+
-40°C to +125°C
10 μMAX
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Chip Information
PROCESS: BiCMOS
www.maximintegrated.com
For the latest package outline information and land patterns
(footprints), go to www.maximintegrated.com/packages. Note
that a “+”, “#”, or “-” in the package code indicates RoHS status
only. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
10 TDFN-EP
T1032N+1
21-0429
90-0082
10 μMAX
U10+5
21-0061
90-0330
Maxim Integrated │ 19
MAX17531
42V, 50mA, Ultra-Small, High-Efficiency
Synchronous Step-Down DC-DC Converter
with 22µA No-Load Supply Current
Revision History
REVISION
NUMBER
REVISION
DATE
0
11/14
DESCRIPTION
Initial release
PAGES
CHANGED
—
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.
© 2014 Maxim Integrated Products, Inc. │ 20