MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
����������������������������������������������������������������� Maxim Integrated Products 1
19-6244; Rev 0; 5/12
Ordering Information appears at end of data sheet.
Typical Operating Circuit
For related parts and recommended products to use with this part, refer to www.maxim-ic.com/MAX17501.related.
General Description
The MAX17501 high-efficiency, high-voltage, synchro-
nous step-down DC-DC converter operates over a 4.5V to
60V input voltage range and is designed for a wide range
of applications. The ultra-wide-input operation makes it
ideal for not only industrial control and building automa-
tion, but also base stations, telecom, home entertainment
and automotive applications. It delivers output currents
up to 500mA, at output voltages of 3.3V and 5V. The out-
put voltage is accurate within Q1.6% over temperature.
The device operates over the -40NC to +125NC industrial
temperature range and is available in a tiny, 10-pin (3mm
x 2mm) TDFN with an exposed pad.
The device features peak-current-mode control with
pulse-width modulation (PWM). The PWM operation
ensures constant switching frequency at all operating
conditions. The low-resistance, on-chip, pMOS/nMOS
switches ensure high efficiency at full load while minimiz-
ing the critical inductances, making the layout a much
simpler task compared to discrete solutions.
The device offers fixed switching frequency of 600kHz. To
reduce input inrush current, the device offers an adjust-
able voltage soft-start feature with an external capacitor
from the SS pin to ground. The device also incorporates
an output enable/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. The device
supports hiccup-mode current-limit protection for low
power dissipation under overload and output short-circuit
conditions.
Applications
Industrial Process Control
HVAC and Building Control
General-Purpose Point-of-Load
Base Station, VOIP, Telecom
Home Theater
Automotive
Battery-Powered Equipment
Benefits and Features
S Eliminate External Components and Reduce Total
Cost
No Schottky-Synchronous Operation for High
Efficiency and Reduced Cost
Internal Compensation for Ultra-Compact
Layout
All-Ceramic Capacitors
S Reduce Number of DC-DC Regulators to Stock
Wide 4.5V to 60V Operating-Voltage Range
Fixed 3.3V and 5V Output
Delivers Up to 500mA Over Temperature
600kHz Switching Frequency
S Reduce Power Dissipation
Peak Efficiency > 90%
Shutdown Current = 1µA (typ)
S Operate Reliably in Adverse Industrial Environments
Hiccup-Mode Current Limit and Autoretry Startup
Built-In Output-Voltage Monitoring (Open-Drain
RESET Pin)
Resistor-Programmable UVLO Threshold
Increased Safety with Adjustable Soft-Start and
Prebiased Power-Up
Optional Adjustable Output and PFM (Available
Upon Factory Request)
-40NC to +125NC Industrial Temperature Range
EVALUATION KIT AVAILABLE
C2
1µF
C3
3300pF
N.C.
SS
VCC
EN/UVLO
VIN LX
PGND
GND
FB/VO
RESET
VIN
24V ±20% C1
1µF
1206 1
2JU1
R1
3.32MI
R2
866kI
3
L1
47µH
C4
10µF, 6.3V
1206
VOUT
5V, 500mA
MAX17501F
RESET
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
����������������������������������������������������������������� Maxim Integrated Products 2
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
VIN to GND ............................................................-0.3V to +70V
EN/UVLO to GND ......................................... -0.3V to VIN + 0.3V
LX to PGND ...........................................................-0.3V to +70V
FB, RESET, COMP, SS to GND ................................. -0.3V to 6V
VCC to GND .............................................................-0.3V to +6V
GND to PGND ......................................................-0.3V to +0.3V
LX Total RMS Current ........................................................ Q1.6A
Output Short-Circuit Duration .................................... Continuous
Continuous Power Dissipation (TA = +70NC)
10-Pin TDFN (derate 14.9mW/NC above +70NC)
(multilayer board) ...................................................1188.7mW
Operating Temperature Range ........................ -40NC to +125NC
Junction Temperature .....................................................+150NC
Storage Temperature Range ............................ -65NC to +160NC
Lead Temperature (soldering, 10s) ................................+300NC
Soldering Temperature (reflow) ......................................+260NC
ABSOLUTE MAXIMUM RATINGS
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.maxim-ic.com/thermal-tutorial.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional opera-
tion 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.
Thermal Resistance
TDFN
Junction-to-Ambient Thermal Resistance (BJA) .......67.3NC/W Junction-to-Case Thermal Resistance (BJC) ............18.2NC/W
PACKAGE THERMAL CHARACTERISTICS (Note 1)
ELECTRICAL CHARACTERISTICS
(VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF, VFB = 0.98 x VOUT, LX = unconnected,
RESET =
unconnected. TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC. All voltages are referenced to GND,
unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
INPUT SUPPLY (VIN)
Input Voltage Range VIN 4.5 60 V
Input Supply Current
IIN-SH VEN = 0V, shutdown mode 0.9 3.5 FA
IIN-SW Normal switching
mode, VCOMP = 0.8V
VIN = 12V 3.7 5.2 mA
VIN = 24V 5 6.75
ENABLE/UVLO (EN/UVLO)
EN Threshold
VENR VEN rising 1.194 1.218 1.236
VVENF VEN falling 1.114 1.135 1.156
VEN-TRUESD VEN falling, true shutdown 0.75
EN Input Leakage Current IEN 7 200 nA
LDO
VCC Output Voltage Range VCC 6V < VIN < 12V, 0mA < IVCC < 10mA,
12V < VIN < 60V, 0mA < IVCC < 2mA 4.65 5 5.35 V
VCC Current Limit IVCC-MAX VCC = 4.3V, VIN = 12V 17 40 80 mA
VCC Dropout VCC-DO VIN = 4.5V, IVCC = 5mA 4.1 V
VCC UVLO VCC-UVR VCC rising 3.85 4 4.15 V
VCC-UVF VCC falling 3.55 3.7 3.85
����������������������������������������������������������������� Maxim Integrated Products 3
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF, VFB = 0.98 x VOUT, LX = unconnected,
RESET =
unconnected. TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC. All voltages are referenced to GND,
unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
LX
LX Leakage Current ILX_LKG VEN = 0V, TA = +25NC,
VLX = (VPGND + 1V) to (VIN - 1V) 1FA
SOFT-START (SS)
Switchover to Internal Reference-
Voltage Threshold VSS-TH 863 880 898 mV
Charging Current ISS VSS = 0.5V 4.7 5 5.3 FA
FEEDBACK (FB)
FB Input Bias Current IFB TA = +25NC
MAX17501E,
VFB = 3.3V 6.8 12 17 FA
MAX17501F,
VFB = 5V 6.8 12 17 FA
OUTPUT VOLTAGE (VOUT)
Output Voltage Range MAX17501E only 3.248 3.3 3.352
MAX17501F only 4.922 5 5.08
CURRENT LIMIT
Peak-Current-Limit Threshold IPEAK-LIMIT 0.585 0.685 0.795 A
Runaway-Current-Limit Threshold IRUNAWAY-
LIMIT 0.73 0.865 1 A
Valley Current-Limit Threshold ISINK-LIMIT 0.3 0.35 0.4 A
TIMING
Switching Frequency fSW
VFB >
VOUT-HICF MAX17501E/F
560 600 640
kHz
VFB <
VOUT-HICF 280 300 320
Events to Hiccup After Crossing
Runaway-Current Limit 1
VOUT Undervoltage Trip Level to
Cause Hiccup VOUT-HICF VSS > 0.95V (soft-start is done) 69.14 71.14 73.14 %
HICCUP Timeout 32,768 Cycles
Minimum On-Time tON_MIN 85 120 ns
Maximum Duty Cycle DMAX VFB = 0.98 x VFB-
REG MAX17501E/F 92 94 96 %
LX Dead Time 5 ns
����������������������������������������������������������������� Maxim Integrated Products 4
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Note 2: All limits are 100% tested at +25NC. Limits over temperature are guaranteed by design.
Note 3: Guaranteed by design, not production tested.
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF, VFB = 0.98 x VOUT, LX = unconnected,
RESET =
unconnected. TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC. All voltages are referenced to GND,
unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
RESET
RESET Output Level Low IRESET = 1mA 0.02 V
RESET Output Leakage Current
High VFB = 1.01 x VOUT, TA = +25NC0.45 FA
VOUT Threshold for RESET
Assertion VOUT-OKF VFB falling 90.5 92.5 94.5 %
VOUT Threshold for RESET
Deassertion VOUT-OKR VFB rising 93.5 95.5 97.5 %
RESET Deassertion Delay After
FB Reaches 95% Regulation 1024 Cycles
THERMAL SHUTDOWN
Thermal-Shutdown Threshold Temperature rising 165 NC
Thermal-Shutdown Hysteresis 10 NC
����������������������������������������������������������������� Maxim Integrated Products 5
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics
(VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF,
VFB = 0.98 x VOUT
, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(MAX17501E)
MAX17501 toc01
EFFICIENCY (%)
60
65
70
75
80
85
90
95
55
100 500
LOAD CURRENT (mA)
450400350300250200150
VIN = 12V
VIN = 24V VIN = 36V
VIN = 48V
EFFICIENCY vs. LOAD CURRENT
(MAX17501F)
MAX17501 toc02
EFFICIENCY (%)
70
75
80
85
90
95
65
100 500
LOAD CURRENT (mA)
450400350300250200150
VIN = 12V
VIN = 24V VIN = 36V
VIN = 48V
OUTPUT VOLTAGE vs. LOAD CURRENT
(MAX17501E)
MAX17501 toc03
OUTPUT VOLTAGE (V)
050 500
LOAD CURRENT (mA)
450400350300250200100 150
VIN = 12V
VIN = 24V
VIN = 36V
VIN = 48V
3.292
3.294
3.296
3.298
3.300
3.302
3.304
3.306
3.308
3.310
3.290
OUTPUT VOLTAGE vs. LOAD CURRENT
(MAX17501F)
MAX17501 toc04
OUTPUT VOLTAGE (V)
050 500
LOAD CURRENT (mA)
450400350300250200100 150
VIN = 36V
VIN = 12V
VIN = 48V
VIN = 24V
4.990
4.995
5.000
5.005
5.010
5.015
4.985
EN/UVLO THRESHOLD VOLTAGE
vs. TEMPERATURE
MAX17501 toc07
EN/UVLO THRESHOLD VOLTAGE (V)
-40 120
TEMPERATURE (°C)
100806040200-20
1.13
1.14
1.15
1.16
1.17
1.18
1.19
1.20
1.21
1.22
1.23
1.12
RISING THRESHOLD
FALLING THRESHOLD
SHUTDOWN CURRENT
vs. TEMPERATURE
MAX17501 toc05
SHUTDOWN CURRENT (µA)
0.75
0.80
0.85
0.90
0.95
1.00
1.05
1.10
0.70
-40 120
TEMPERATURE (°C)
100
806040200-20
OUTPUT VOLTAGE vs. TEMPERATURE
(MAX17501E)
MAX17501 toc08
OUTPUT VOLTAGE (V)
-40 120
TEMPERATURE (°C)
100806040200-20
NO LOAD FULL LOAD
3.285
3.290
3.295
3.300
3.305
3.310
3.315
3.320
3.280
NO-LOAD SWITCHING CURRENT
vs. TEMPERATURE
MAX17501 toc06
NO-LOAD SWITCHING CURRENT (mA)
-40 120
TEMPERATURE (°C)
100806040200-20
4.85
4.90
4.95
5.00
4.80
OUTPUT VOLTAGE vs. TEMPERATURE
(MAX17501F)
MAX17501 toc09
OUTPUT VOLTAGE (V)
-40 120
TEMPERATURE (°C)
100806040200-20
NO LOAD
FULL LOAD
4.96
4.97
4.98
4.99
5.00
5.01
5.02
5.03
5.04
5.05
4.95
����������������������������������������������������������������� Maxim Integrated Products 6
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
(VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF,
VFB = 0.98 x VOUT
, unless otherwise noted.)
PEAK CURRENT LIMIT
vs. TEMPERATURE
MAX17501 toc10
PEAK CURRENT LIMIT (A)
1.0
0.5
-40 120
TEMPERATURE (°C)
100
806040200-20
0.6
0.7
0.8
0.9
RUNAWAY CURRENT LIMIT
vs. TEMPERATURE
MAX17501 toc11
RUNAWAY CURRENT LIMIT (A)
1.0
0.5
-40 120
TEMPERATURE (°C)
100
806040200-20
0.6
0.7
0.8
0.9
SWITCHING FREQUENCY
vs. TEMPERATURE
MAX17501 toc12
SWITCHING FREQUENCY (kHz)
-40 120
TEMPERATURE (°C)
100
806040200-20
520
540
560
580
620
640
660
680
700
500
600
SOFT-START/SHUTDOWN FROM EN/EVLO
(MAX17501E)
MAX17501 toc13
1ms/div
EN/UVLO
2V/div
VOUT
1V/div
IOUT
200mA/div
RESET
2V/div
SOFT-START FROM VIN
(MAX17501F)
MAX17501 toc16
400µs/div
VIN
20V/div
IOUT
200mA/div
VOUT
2V/div
RESET
5V/div
SOFT-START/SHUTDOWN FROM EN/EVLO
(MAX17501F)
MAX17501 toc14
1ms/div
EN/UVLO
2V/div
VOUT
2V/div
IOUT
200mA/div
RESET
5V/div
SOFT-START FROM VIN
(MAX17501E)
MAX17501 toc15
400µs/div
VIN
20V/div
IOUT
200mA/div
VOUT
1V/div
RESET
2V/div
SOFT-START WITH 2V PREBIAS
(MAX17501E)
MAX17501 toc17
400µs/div
EN/UVLO
2V/div
VOUT
1V/div
RESET
2V/div
SOFT-START WITH 2.5V PREBIAS
(MAX17501F)
MAX17501 toc18
400µs/div
EN/UVLO
2V/div
VOUT
1V/div
RESET
5V/div
����������������������������������������������������������������� Maxim Integrated Products 7
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
(VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF,
VFB = 0.98 x VOUT
, unless otherwise noted.)
LOAD TRANSIENT RESPONSE OF
MAX17501E (LOAD CURRENT STEPPED
FROM NO LOAD TO 250mA)
MAX17501 toc19
20µs/div
VOUT (AC)
50mV/div
IOUT
100mA/div
LOAD TRANSIENT RESPONSE OF
MAX17501F (LOAD CURRENT STEPPED
FROM NO LOAD TO 250mA)
MAX17501 toc20
20µs/div
VOUT (AC)
100mV/div
IOUT
200mA/div
LOAD TRANSIENT RESPONSE OF
MAX17501E (LOAD CURRENT STEPPED
FROM 250mA TO 500mA)
MAX17501 toc21
20µs/div
VOUT (AC)
50mV/div
IOUT
200mA/div
LOAD TRANSIENT RESPONSE OF
MAX17501F (LOAD CURRENT STEPPED
FROM 250mA TO 500mA)
MAX17501 toc22
20µs/div
VOUT (AC)
100mV/div
IOUT
200mA/div
SWITCHING WAVEFORMS OF
MAX17501F AT 500mA LOAD
MAX17501 toc23
2µs/div
VOUT (AC)
50mV/div
ILX
500mA/div
LX
10V/div
OUTPUT OVERLOAD PROTECTION OF
MAX17501F
MAX17501 toc24
20ms/div
VOUT
2V/div
IOUT
200mA/div
BODEPLOT OF MAX17501E
AT 500mA LOAD
MAX17501 toc25
BW = 62kHz
PM = 59°
44556677889911223
BODEPLOT OF MAX17501F
AT 500mA LOAD
MAX17501 toc26
BW = 35kHz
PM = 73°
44556677889911223
����������������������������������������������������������������� Maxim Integrated Products 8
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Pin Description
Pin Configuration
PIN NAME FUNCTION
1 PGND Power Ground. Connect PGND externally to the power ground plane. Connect GND and PGND
pins together at the ground return path of the VCC bypass capacitor.
2 VIN Power-Supply Input. The input supply range is from 4.5V to 60V.
3 EN/UVLO
Enable/Undervoltage Lockout Input. Drive EN/UVLO high to enable the output voltage. Connect
to the center of resistive divider between VIN and GND to set the input voltage (undervoltage
threshold) at which the device turns on. Pull up to VIN for always on.
4 VCC 5V LDO Output. Bypass VCC with 1FF ceramic capacitance to GND.
5 FB Feedback Input. Directly connect FB to the output.
6 SS Soft-Start Input. Connect a capacitor from SS to GND to set the soft-start time.
7 N.C. No Connection. Leave unconnected.
8RESET Open-Drain RESET Output. The RESET output is driven low if FB drops below 92.5% of its set
value. RESET goes high 1024 clock cycles after FB rises above 95.5% of its set value.
9 GND Analog Ground
10 LX Switching Node. Connect LX to the switching side of the inductor. LX is high impedance when the
device is in shutdown mode.
— EP Exposed Pad. Connect to the GND pin of the IC. Connect to a large copper plane below the IC to
improve heat dissipation capability.
TOP VIEW
*EP = EXPOSED PAD, CONNECTED TO GND
TDFN
(3mm x 2mm)
MAX17501
1
2
3
4
5
PGND
VIN
EN/UVLO
VCC
FB
LX
GND
RESET
N.C.
SS
+
EP*
10
9
8
7
6
����������������������������������������������������������������� Maxim Integrated Products 9
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Block Diagram
PGND
LX
VIN
VCC LDO
SLOPE COMPENSATION
START
RESET
LOGIC
REFERENCE
SWITCHOVER
LOGIC
COMP
CURRENT
SENSE
P DRIVER
PWM
LOGIC
GM
GND
INTERNAL COMPENSATION
N DRIVER
VCC
5µA
SS
RESET
SS
HICCUP
COMP
HICCUP
CLK OSC
PWM
COMPARATOR
EN/UVLO
SS
900mV
FB
MAX17501
���������������������������������������������������������������� Maxim Integrated Products 10
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Detailed Description
The MAX17501 step-down regulator operates from 4.5V
to 60V and delivers up to 500mA load current. Output
voltage regulation accuracy meets Q1.6% over load, line,
and temperature.
The device uses a peak-current-mode-control scheme. It
employs synchronous rectification. An internal transcon-
ductance error amplifier produces 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 p-channel 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
n-channel MOSFET turns on. 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 enable/undervoltage lockout
(EN/UVLO), adjustable soft-start time (SS), and open-
drain reset output (RESET) functionality.
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 VCC linear regulator
should be bypassed with a 1FF ceramic capacitor to
GND. The device employs an undervoltage-lockout circuit
that disables the internal linear regulator when VCC falls
below 3.7V (typ). The 300mV UVLO hysteresis
prevents
chattering on power-up/power-down. The internal VCC
linear regulator can source up to 40mA (typ) to supply
the device and to power the low-side gate driver.
Switching Frequency
The devices have a fixed 600kHz switching frequency.
The minimum duty ratio at which the devices can oper-
ate is 7.7%.
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 800mA (typ). A runaway-current limit on the high-
side switch current at 900mA (typ) protects the device
under high input voltage, short-circuit conditions when
there is insufficient output voltage available to restore the
inductor current that 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, output voltage drops to 71.1% (typ) of
its nominal value 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.
RESET Output
The device includes a RESET comparator to monitor the
output voltage. The open-drain RESET output requires
an external pullup resistor. RESET can sink 2mA of
current while low. RESET goes high (high impedance)
1024 switching cycles after the regulator output increases
above 95.5% of the designed nominal regulated voltage.
RESET goes low when the regulator output voltage drops
to below 92.5% of the nominal regulated voltage. RESET
goes low during thermal shutdown.
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 first with the high-side
switch. The output voltage is then smoothly ramped up to
the target value in alignment with the internal reference.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipa-
tion in the device. When the junction temperature of
the device exceeds +165NC, an on-chip thermal sensor
shuts down the device, allowing the device to cool. The
thermal sensor turns the device on again after the junc-
tion temperature cools by 10NC. Soft-start resets during
thermal shutdown. Carefully evaluate the total power
dissipation (see the Power Dissipation section) to avoid
unwanted triggering of the thermal-overload protection in
normal operation.
���������������������������������������������������������������� Maxim Integrated Products 11
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Applications Information
Input Capacitor Selection
The discontinuous input-current waveform of the buck
converter causes large ripple currents in the input
capacitor. The switching frequency, peak inductor cur-
rent, and the allowable peak-to-peak voltage ripple
that reflects back to the source dictate the capacitance
requirement. The device’s high switching frequency
allows the use of smaller value input capacitors. X7R
capacitors are recommended in industrial applications
for their temperature stability. A minimum value of 1FF
should be used for the input capacitor. Higher values
help reduce the ripple on the input DC bus further. In
applications where the source is located distant from
the device input, an electrolytic capacitor should be
added in parallel to the 1FF ceramic capacitor to provide
necessary damping for potential oscillations caused by
the longer input power path and input ceramic capacitor.
Inductor Selection
Three key inductor parameters must be specified
for operation with the device: inductance value (L),
inductor saturation current (ISAT), and DC resistance
(RDCR). To determine the inductance value, select the
ratio of inductor peak-to-peak ripple current to the DC
average current (LIR). For LIR values that are too high,
the RMS currents are high, and therefore the inductor
I2R losses are high. For LIR values that are too low,
the inductance values are high and consequently the
inductor DC resistance is also high, and therefore
inductor I2R losses are high as well. A good compromise
between size and loss is a 30% peak-to-peak ripple
current to average-current ratio (LIR = 0.3).
The switching
frequency, input voltage, output voltage, and selected LIR
determine the inductor value as follows:
OUT IN OUT
IN SW OUT
V (V - V )
L=V f I LIR
×
×× ×
where VIN, VOUT, and IOUT are nominal values. The
switching frequency is 600kHz for the MAX17501E/
MAX17501F. 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 (IPEAK-LIMIT
(typ) = 0.8A for the device). A variety of inductors from
different suppliers are available to meet this requirement
(e.g., inductors from the Coilcraft LPS6235 series).
See Table 1 to select inductors for 5V and 3.3V fixed
output-voltage applications based on the MAX17501E/
MAX17501F.
Output Capacitor Selection
X7R ceramic output capacitors are preferred due to their
stability over temperature in industrial applications. The
output capacitor is usually sized to support a step load
of 50% 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:
STEP RESPONSE
OUT OUT
RESPONSE C SW
1I t
C2V
0.33 1
t ()
ff
×
= × ∆
≅+
where ISTEP is the load current step, tRESPONSE is the
response time of the controller, DVOUT is the allowable
output-voltage deviation, fC is the target closed-loop
crossover frequency, and fSW is the switching frequency.
fC is generally chosen to be 1/8 to 1/10 of fSW.
Use Table 2 to select output capacitors for fixed 5V
and 3.3V output-voltage applications based on the
MAX17501E/MAX17501F.
Table 1. Inductor Selection
VOUT (V) IOUT (max) (mA) L (µH) MINIMUM ISAT (mA) SUGGESTED PART
5 500 47 800 Coilcraft LPS6235-473ML_
3.3 500 33 800 Coilcraft LPS6235-333ML_
���������������������������������������������������������������� Maxim Integrated Products 12
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Soft-Start Capacitor Selection
The device implements adjustable soft-start operation for
the synchronous step-down converter. A capacitor con-
nected from the SS pin to GND programs the soft-start
period.
The soft-start time (tSS) is related to the capacitor
connected at SS (CSS) by the following equation:
SS SS
C 5.55 t= ×
where tSS is in milliseconds and CSS is in nanofarads.
For example, to have a 1.8ms soft-start time, a 10nF
capacitor should be connected from the SS pin to GND.
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 GND (see Figure 1). Connect the center node of the
divider to EN/UVLO.
Choose R1 to be 3.3MI, and then calculate R2 as follows:
INU
R1 1.218
R2 (V -1.218)
×
=
where VINU is the voltage at which the device is required
to turn on.
Power Dissipation
It should be ensured that the junction temperature of the
device does not exceed +125NC 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:
()
2
LOSS OUT DCR
OUT
OUT OUT OUT
1
P P -1 - I R
P VI
=××
η
= ×
where P
OUT
is the output power, E is is the efficiency of the
device, and R
DCR
is the DC resistance of the output
Inductor (see the Typical Operating Characteristics for more
information on efficiency at typical operating conditions).
The maximum power that can be dissipated in the
device’s 10-pin TDFN-EP package is 1188.7mW at
+70NC temperature. The power dissipation capability
should be derated as the temperature goes above
+70NC at 14.9mW/NC. For a multilayer board, the thermal
performance metrics for the package are given below:
BJA = 67.3NC/W
BJC = 18.2NC/W
The junction temperature of the device can be estimated
at any given maximum ambient temperature (TA_MAX)
from the following equation:
( )
J_MAX A_MAX JA LOSS
TT P= +θ ×
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:
( )
J_MAX EP_MAX JC LOSS
TT P= +θ ×
Table 2. Output Capacitor Selection
Figure 1. Adjustable EN/UVLO Network
VOUT (V) IOUT (max) (mA) TYPE VOLTAGE RATING (V) SUGGESTED PART
5 500 10FF/1206/X7R 6.3 Murata GRM31CR70J106KA01L
3.3 500 10FF/1206/X7R 6.3 Murata GRM31CR70J106KA01L
VIN
EN/UVLO
GND
R2
R1
���������������������������������������������������������������� Maxim Integrated Products 13
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
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 pin of the device. This eliminates as much trace
inductance effects as possible and gives the device a
cleaner voltage supply. The bypass capacitor for the VCC
pin should also be placed close to the pin to reduce effects
of trace impedance. The feedback trace should be routed
as far as possible from the inductor.
When routing the circuitry around the device, the analog
small-signal ground and the power ground for switch-
ing 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. This helps to keep the analog ground
quiet. The ground plane should be kept continuous/
unbroken as much 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 device, for efficient heat dissipation. Several
vias in parallel have lower impedance than a single via.
For a sample layout that ensures first-pass success,
refer to the MAX17501 evaluation kit layout available at
www.maxim-ic.com.
���������������������������������������������������������������� Maxim Integrated Products 14
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Figure 2. MAX17501F Application Circuit (5V Output, 500mA Maximum Load Current, 600kHz Switching Frequency)
Figure 3. MAX17501E Application Circuit (3.3V Output, 500mA Maximum Load Current, 600kHz Switching Frequency)
Typical Applications Circuits
C2
1µF
C3
3300pF
N.C.
SS
VCC
EN/UVLO
VIN LX
PGND
GND
FB
RESET
VIN
24V ±20% C1
1µF
1206 1
2JU1
R1
3.32MI
R2
866kI
3
L1
47µH
C4
10µF, 6.3V
1206
VOUT
5V, 500mA
MAX17501F
RESET
C2
1µF
C3
3300pF
N.C.
SS
VCC
EN/UVLO
VIN LX
PGND
GND
FB
RESET
VIN
24V ±20% C1
1µF
1206 1
2JU1
R1
3.32MI
R2
866kI
3
RESET
L1
33µH
C4
10µF, 6.3V
1206
VOUT
3.3V, 500mA
MAX17501E
���������������������������������������������������������������� Maxim Integrated Products 15
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maxim-ic.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.
Chip Information
PROCESS: BiCMOS
Ordering Information/Selector Guide
Note: All devices are specified over the -40°C to +125°C operating temperature range. Optional variants available to support
adjustable output and PFM. Contact your Maxim sales representative for more information.
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
10 TDFN-EP T1032N+1 21-0429 90-0082
PART PIN-PACKAGE OUTPUT
VOLTAGE
SWITCHING
FREQUENCY
PEAK-CURRENT-MODE
CONTROL SCHEME
OUTPUT
CURRENT
MAX17501EATB+ 10 TDFN-EP* 3.3V 600kHz Forced PWM 500mA
MAX17501FATB+ 10 TDFN-EP* 5V 600kHz Forced PWM 500mA
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 Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 16
© 2012 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 5/12 Initial release —
