Maxim MAX17501 60v, 500ma, ultra-small, high-efficiency,synchronous step-down dc-dc converter Datasheet

19-6244; Rev 0; 5/12
EVALUATION KIT AVAILABLE
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
General Description
The MAX17501 high-efficiency, high-voltage, synchronous 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 automation, 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 output 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 minimizing 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 adjustable 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
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
Typical Operating Circuit
VIN
24V ±20%
L1
47µH
C1
1µF
1206
HVAC and Building Control
1
JU1 2
3
General-Purpose Point-of-Load
Base Station, VOIP, Telecom
Home Theater
Automotive
LX
VIN
R1
3.32MI
EN/UVLO
R2
866kI
C4
10µF, 6.3V
1206
VOUT
5V, 500mA
PGND
MAX17501F
GND
VCC
C2
1µF
C3
3300pF
SS
N.C.
FB/VO
RESET
RESET
Battery-Powered Equipment
Ordering Information appears at end of data sheet.
For related parts and recommended products to use with this part, refer to www.maxim-ic.com/MAX17501.related.
����������������������������������������������������������������� Maxim Integrated Products 1
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.
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
ABSOLUTE MAXIMUM RATINGS
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
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)
Thermal Resistance
TDFN
Junction-to-Ambient Thermal Resistance (BJA)........67.3NC/W
Junction-to-Case Thermal Resistance (BJC).............18.2NC/W
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
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
60
V
0.9
3.5
FA
VIN = 12V
3.7
5.2
VIN = 24V
5
6.75
INPUT SUPPLY (VIN)
Input Voltage Range
Input Supply Current
VIN
4.5
IIN-SH
VEN = 0V, shutdown mode
IIN-SW
Normal switching
mode, VCOMP = 0.8V
VENR
VEN rising
1.194
1.218
1.236
VENF
VEN falling
1.114
1.135
1.156
V
7
200
nA
4.65
5
5.35
V
40
80
mA
mA
ENABLE/UVLO (EN/UVLO)
EN Threshold
VEN-TRUESD
EN Input Leakage Current
VEN falling, true shutdown
0.75
IEN
LDO
VCC Output Voltage Range
VCC Current Limit
VCC Dropout
VCC UVLO
VCC
6V < VIN < 12V, 0mA < IVCC < 10mA,
12V < VIN < 60V, 0mA < IVCC < 2mA
IVCC-MAX
VCC = 4.3V, VIN = 12V
17
VCC-DO
VIN = 4.5V, IVCC = 5mA
4.1
VCC-UVR
VCC rising
3.85
4
4.15
VCC-UVF
VCC falling
3.55
3.7
3.85
V
V
����������������������������������������������������������������� Maxim Integrated Products 2
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
1
FA
LX
LX Leakage Current
ILX_LKG
VEN = 0V, TA = +25NC,
VLX = (VPGND + 1V) to (VIN - 1V)
SOFT-START (SS)
Switchover to Internal ReferenceVoltage Threshold
Charging Current
VSS-TH
ISS
863
880
898
mV
4.7
5
5.3
FA
MAX17501E,
VFB = 3.3V
6.8
12
17
FA
MAX17501F,
VFB = 5V
6.8
12
17
FA
MAX17501E only
3.248
3.3
3.352
MAX17501F only
4.922
5
5.08
VSS = 0.5V
FEEDBACK (FB)
FB Input Bias Current
IFB
TA = +25NC
OUTPUT VOLTAGE (VOUT)
Output Voltage Range
CURRENT LIMIT
Peak-Current-Limit Threshold
IPEAK-LIMIT
0.585
0.685
0.795
A
Runaway-Current-Limit Threshold
IRUNAWAY-
0.73
0.865
1
A
Valley Current-Limit Threshold
ISINK-LIMIT
0.3
0.35
0.4
A
560
600
640
280
300
320
LIMIT
TIMING
Switching Frequency
fSW
VFB >
VOUT-HICF
VFB <
VOUT-HICF
MAX17501E/F
kHz
Events to Hiccup After Crossing
Runaway-Current Limit
VOUT Undervoltage Trip Level to
Cause Hiccup
1
VOUT-HICF
VSS > 0.95V (soft-start is done)
69.14
HICCUP Timeout
73.14
32,768
Minimum On-Time
Maximum Duty Cycle
LX Dead Time
71.14
tON_MIN
DMAX
VFB = 0.98 x VFBREG
MAX17501E/F
92
%
Cycles
85
120
ns
94
96
%
5
ns
����������������������������������������������������������������� 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
RESET
RESET Output Level Low
IRESET = 1mA
0.02
V
RESET Output Leakage Current
High
VFB = 1.01 x VOUT, TA = +25NC
0.45
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
165
NC
10
NC
THERMAL SHUTDOWN
Thermal-Shutdown Threshold
Temperature rising
Thermal-Shutdown Hysteresis
Note 2: All limits are 100% tested at +25NC. Limits over temperature are guaranteed by design.
Note 3: Guaranteed by design, not production tested.
����������������������������������������������������������������� Maxim Integrated Products 4
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
(MAX17501F)
VIN = 48V
VIN = 36V
VIN = 48V
VIN = 24V
75
VIN = 36V
65
70
VIN = 12V
55
3.290
5.005
5.000
4.995
VIN = 36V
VIN = 12V
1.10
1.05
4.990
1.00
0.95
0.90
0.85
0.80
0.75
-40 -20
EN/UVLO THRESHOLD VOLTAGE
vs. TEMPERATURE
1.21
1.20
RISING THRESHOLD
1.19
1.18
1.17
1.16
FALLING THRESHOLD
1.15
1.14
40
60
-40
-20
0
20
40
60
TEMPERATURE (°C)
80 100 120
4.85
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (°C)
OUTPUT VOLTAGE vs. TEMPERATURE
(MAX17501E)
OUTPUT VOLTAGE vs. TEMPERATURE
(MAX17501F)
3.310
3.305
3.300
NO LOAD
3.295
FULL LOAD
3.290
5.05
5.04
5.03
5.02
NO LOAD
5.01
5.00
4.99
4.98
FULL LOAD
4.97
4.96
3.280
1.12
4.90
TEMPERATURE (°C)
3.285
1.13
4.95
4.80
80 100 120
3.315
OUTPUT VOLTAGE (V)
1.22
20
3.320
MAX17501 toc07
1.23
0
OUTPUT VOLTAGE (V)
50 100 150 200 250 300 350 400 450 500
LOAD CURRENT (mA)
MAX17501 toc08
0
50 100 150 200 250 300 350 400 450 500
LOAD CURRENT (mA)
5.00
0.70
4.985
EN/UVLO THRESHOLD VOLTAGE (V)
0
NO-LOAD SWITCHING CURRENT
vs. TEMPERATURE
MAX17501 toc05
MAX17501 toc04
VIN = 48V
VIN = 24V
VIN = 12V
3.296
SHUTDOWN CURRENT
vs. TEMPERATURE
SHUTDOWN CURRENT (µA)
OUTPUT VOLTAGE (V)
5.010
VIN = 24V
3.298
100 150 200 250 300 350 400 450 500
LOAD CURRENT (mA)
OUTPUT VOLTAGE vs. LOAD CURRENT
(MAX17501F)
5.015
3.300
3.292
65
100 150 200 250 300 350 400 450 500
LOAD CURRENT (mA)
3.302
3.294
VIN = 12V
NO-LOAD SWITCHING CURRENT (mA)
60
3.304
MAX17501 toc06
VIN = 24V
80
VIN = 36V
3.306
MAX17501 toc09
70
85
VIN = 48V
3.308
OUTPUT VOLTAGE (V)
80
75
90
EFFICIENCY (%)
85
3.310
MAX17501 toc02
90
EFFICIENCY (%)
95
MAX17501 toc01
95
OUTPUT VOLTAGE vs. LOAD CURRENT
(MAX17501E)
MAX17501 toc03
EFFICIENCY vs. LOAD CURRENT
(MAX17501E)
4.95
-40
-20
0
20
40
60
TEMPERATURE (°C)
80 100 120
-40
-20
0
20
40
60
80 100 120
TEMPERATURE (°C)
����������������������������������������������������������������� Maxim Integrated Products 5
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.)
RUNAWAY CURRENT LIMIT
vs. TEMPERATURE
0.8
0.7
0.6
0.9
0.8
0.7
0.6
700
MAX17501 toc12
MAX17501 toc11
MAX17501 toc10
0.9
1.0
RUNAWAY CURRENT LIMIT (A)
PEAK CURRENT LIMIT (A)
1.0
SWITCHING FREQUENCY
vs. TEMPERATURE
680
SWITCHING FREQUENCY (kHz)
PEAK CURRENT LIMIT
vs. TEMPERATURE
660
640
620
600
580
560
540
520
0.5
0.5
-40 -20
0
20
40
60
100 120
80
500
-40 -20
0
20
40
60
80
100 120
-40 -20
0
20
40
60
100 120
80
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
SOFT-START/SHUTDOWN FROM EN/EVLO
(MAX17501E)
SOFT-START/SHUTDOWN FROM EN/EVLO
(MAX17501F)
SOFT-START FROM VIN
(MAX17501E)
MAX17501 toc13
EN/UVLO
2V/div
VOUT
1V/div
IOUT
200mA/div
EN/UVLO
2V/div
VIN
20V/div
VOUT
2V/div
IOUT
200mA/div
IOUT
200mA/div
VOUT
1V/div
RESET
5V/div
RESET
2V/div
MAX17501 toc15
MAX17501 toc14
RESET
2V/div
1ms/div
1ms/div
400µs/div
SOFT-START FROM VIN
(MAX17501F)
SOFT-START WITH 2V PREBIAS
(MAX17501E)
SOFT-START WITH 2.5V PREBIAS
(MAX17501F)
MAX17501 toc16
VIN
20V/div
IOUT
200mA/div
VOUT
2V/div
RESET
5V/div
400µs/div
MAX17501 toc18
MAX17501 toc17
EN/UVLO
2V/div
EN/UVLO
2V/div
VOUT
1V/div
VOUT
1V/div
RESET
2V/div
RESET
5V/div
400µs/div
400µs/div
����������������������������������������������������������������� 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.)
LOAD TRANSIENT RESPONSE OF
MAX17501E (LOAD CURRENT STEPPED
FROM NO LOAD TO 250mA)
LOAD TRANSIENT RESPONSE OF
MAX17501F (LOAD CURRENT STEPPED
FROM NO LOAD TO 250mA)
LOAD TRANSIENT RESPONSE OF
MAX17501E (LOAD CURRENT STEPPED
FROM 250mA TO 500mA)
MAX17501 toc20
MAX17501 toc21
MAX17501 toc19
VOUT (AC)
100mV/div
VOUT (AC)
50mV/div
VOUT (AC)
50mV/div
IOUT
200mA/div
IOUT
200mA/div
IOUT
100mA/div
20µs/div
20µs/div
20µs/div
LOAD TRANSIENT RESPONSE OF
MAX17501F (LOAD CURRENT STEPPED
FROM 250mA TO 500mA)
SWITCHING WAVEFORMS OF
MAX17501F AT 500mA LOAD
OUTPUT OVERLOAD PROTECTION OF
MAX17501F
MAX17501 toc23
MAX17501 toc22
MAX17501 toc24
VOUT (AC)
50mV/div
VOUT (AC)
100mV/div
VOUT
2V/div
ILX
500mA/div
IOUT
200mA/div
LX
10V/div
2µs/div
20µs/div
BODEPLOT OF MAX17501E
AT 500mA LOAD
MAX17501 toc25
BW = 62kHz
PM = 59°
4 5 6 7 8 91
IOUT
200mA/div
20ms/div
BODEPLOT OF MAX17501F
AT 500mA LOAD
MAX17501 toc26
BW = 35kHz
PM = 73°
2
3 4 5 6 7 891
2
4 5 6 7 8 91
2
3 4 5 6 7 891
2
����������������������������������������������������������������� Maxim Integrated Products 7
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Pin Configuration
TOP VIEW
MAX17501
10
LX
2
9
GND
EN/UVLO
3
8
RESET
VCC
4
7
N.C.
FB
5
6
SS
PGND
1
VIN
+
EP*
TDFN
(3mm x 2mm)
*EP = EXPOSED PAD, CONNECTED TO GND
Pin Description
PIN
NAME
FUNCTION
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.
1
PGND
2
VIN
3
EN/UVLO
4
VCC
5
FB
5V LDO Output. Bypass VCC with 1FF ceramic capacitance to GND.
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.
8
RESET
9
GND
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.
Power-Supply Input. The input supply range is from 4.5V to 60V.
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.
No Connection. Leave unconnected.
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.
Analog Ground
����������������������������������������������������������������� Maxim Integrated Products 8
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Block Diagram
VCC
PGND
N DRIVER
5µA
SS
LX
MAX17501
HICCUP
SS
P DRIVER
VIN
CURRENT
SENSE
VCC
PWM
COMPARATOR
LDO
CLK
PWM
LOGIC
OSC
COMP
HICCUP
SLOPE COMPENSATION
START
EN/UVLO
RESET
LOGIC
SS
900mV
RESET
COMP
REFERENCE
SWITCHOVER
LOGIC
GM
FB
INTERNAL COMPENSATION
GND
����������������������������������������������������������������� Maxim Integrated Products 9
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 transconductance 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 opendrain 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 operate is 7.7%.
Overcurrent Protection/Hiccup Mode
The device is provided with a robust overcurrentprotection 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 highside 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 runawaycurrent 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. 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.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation 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 junction 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 10
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 current, 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:
L=
VOUT × (VIN - VOUT )
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:
C OUT=
1 I STEP × t RESPONSE
×
∆VOUT
2
t RESPONSE ≅ (
0.33
fC
+
1
fSW
)
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.
VIN × fSW × IOUT × LIR
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 11
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Table 2. Output Capacitor Selection
VOUT (V)
IOUT (max) (mA)
TYPE
VOLTAGE RATING (V)
5
500
10FF/1206/X7R
6.3
Murata GRM31CR70J106KA01L
3.3
500
10FF/1206/X7R
6.3
Murata GRM31CR70J106KA01L
Soft-Start Capacitor Selection
The device implements adjustable soft-start operation for
the synchronous step-down converter. A capacitor connected 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:
C=
SS 5.55 × t SS
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 undervoltagelockout 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:
R2 =
R1× 1.218
(VINU -1.218)
where VINU is the voltage at which the device is required
to turn on.
VIN
SUGGESTED PART
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:
(

 1 
2
PLOSS =×
POUT  -1 - IOUT × R DCR
 η 

P=
OUT VOUT × IOUT
)
where POUT is the output power, E is is the efficiency of the
device, and RDCR 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:
TJ_MAX
= TA_MAX + (θ JA × PLOSS )
R1
EN/UVLO
R2
GND
Figure 1. Adjustable EN/UVLO Network
If the application has a thermal-management system that
ensures that the exposed pad of the device is maintained
at a given temperature (TEP_MAX) by using proper heat
sinks, then the junction temperature of the device can be
estimated at any given maximum ambient temperature
from the equation below:
T=
J_MAX TEP_MAX + (θ JC × PLOSS )
���������������������������������������������������������������� Maxim Integrated Products 12
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 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. 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 13
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Typical Applications Circuits
VIN
24V ±20%
L1
47µH
LX
VIN
C1
1µF
1206
C4
10µF, 6.3V
1206
R1
3.32MI
1
JU1 2
3
PGND
EN/UVLO
R2
866kI
VOUT
5V, 500mA
MAX17501F
GND
VCC
C2
1µF
FB
SS
C3
3300pF
N.C.
RESET
RESET
Figure 2. MAX17501F Application Circuit (5V Output, 500mA Maximum Load Current, 600kHz Switching Frequency)
VIN
24V ±20%
L1
33µH
LX
VIN
C1
1µF
1206
1
JU1 2
3
C4
10µF, 6.3V
1206
R1
3.32MI
EN/UVLO
R2
866kI
VOUT
3.3V, 500mA
PGND
MAX17501E
GND
VCC
C2
1µF
C3
3300pF
SS
N.C.
FB
RESET
RESET
Figure 3. MAX17501E Application Circuit (3.3V Output, 500mA Maximum Load Current, 600kHz Switching Frequency)
���������������������������������������������������������������� Maxim Integrated Products 14
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Ordering Information /Selector Guide
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
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.
Chip Information
PROCESS: BiCMOS
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.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
10 TDFN-EP
T1032N+1
21-0429
90-0082
���������������������������������������������������������������� Maxim Integrated Products 15
MAX17501
60V, 500mA, Ultra-Small, High-Efficiency,
Synchronous Step-Down DC-DC Converter
Revision History
REVISION
NUMBER
REVISION
DATE
0
5/12
DESCRIPTION
Initial release
PAGES
CHANGED
—
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
©
2012 Maxim Integrated Products
16
Maxim is a registered trademark of Maxim Integrated Products, Inc.
Similar pages