General Description
The MAX5033 easy-to-use, high-efficiency, high-voltage,
step-down DC-DC converter operates from an input volt-
age up to 76V and consumes only 270μA quiescent cur-
rent at no load. This pulse-width modulated (PWM) con-
verter operates at a fixed 125kHz switching frequency at
heavy loads, and automatically switches to pulseskipping
mode to provide low quiescent current and high efficiency
at light loads. The MAX5033 includes internal frequency
compensation simplifying circuit implementation. The
device uses an internal low-onresistance, high-voltage,
DMOS transistor to obtain high efficiency and reduce
overall system cost. This device includes undervoltage
lockout, cycle-by-cycle current limit, hiccup-mode output
short-circuit protection, and thermal shutdown.
The MAX5033 delivers up to 500mA output current. The
output current may be limited by the maximum power
dissipation capability of the package. External shutdown
is included, featuring 10μA (typ) shutdown current. The
MAX5033A/B/C versions have fixed output voltages of
3.3V, 5V, and 12V, respectively, while the MAX5033D fea-
tures an adjustable output voltage, from 1.25V to 13.2V.
The MAX5033 is available in space-saving 8-pin SO and
8-pin plastic DIP packages and operates over the auto-
motive (-40°C to +125°C) temperature range.
Applications
●Consumer Electronics
●Industrial
●Distributed Power
Features
●Wide 7.5V to 76V Input Voltage Range
●Fixed (3.3V, 5V, 12V) and Adjustable (1.25V to
13.2V) Voltage Versions
●500mA Output Current
●Efficiency Up to 94%
● Internal 0.4Ω High-Side DMOS FET
● 270μA Quiescent Current at No Load, 10μA
Shutdown Current
● Internal Frequency Compensation
● Fixed 125kHz Switching Frequency
● Thermal Shutdown and Short-Circuit Current Limit
●8-Pin SO and PDIP Packages
This product is available in both leaded(Pb) and lead(Pb)-free
packages. To order the lead(Pb)-free package, add a + after
the part number.
PART TEMP RANGE PIN-
PACKAGE
OUTPUT
VOLTAGE (V)
MAX5033AUSA 0°C to +85°C 8 SO
3.3MAX5033AUPA 0°C to +85°C 8 PDIP
MAX5033AASA -40°C to +125°C 8 SO
MAX5033BUSA 0°C to +85°C 8 SO
5.0MAX5033BUPA 0°C to +85°C 8 PDIP
MAX5033BASA -40°C to +125°C 8 SO
MAX5033CUSA 0°C to +85°C 8 SO
12MAX5033CUPA 0°C to +85°C 8 PDIP
MAX5033CASA -40°C to +125°C 8 SO
MAX5033DUSA 0°C to +85°C 8 SO
ADJMAX5033DUPA 0°C to +85°C 8 PDIP
MAX5033DASA -40°C to +125°C 8 SO
MAX5033
GND
BST
LX
VIN
SGND
FB
D1
50SQ100
VD
220µH VOUT
5V, 0.5A
VIN
7.5V TO 76V
47µF
0.1µF
0.1µF
33µF
ON
OFF
R1
R2
ON/OFF
1
2
3
4
BST
VD
SGND
FB
8
7
6
5
LX
VIN
GND
ON/OFF
MAX5033
SO/PDIP
Pin Conguration
MAX5033 500mA, 76V, High-Efficiency, MAXPower
Step-Down DC-DC Converter
19-2979; Rev 5; 4/14
Typical Application Circuit
Ordering Information
EVALUATION KIT AVAILABLE
(Voltages referenced to GND, unless otherwise specified.)
VIN .........................................................................-0.3V to +80V
SGND ....................................................................-0.3V to +0.3V
LX.................................................................-0.8V to (VIN + 0.3V)
BST...............................................................-0.3V to (VIN + 10V)
BST (transient < 100ns)................................-0.3V to (VIN + 15V)
BST to LX................................................................-0.3V to +10V
BST to LX (transient < 100ns) ................................-0.3V to +15V
ON/OFF ..................................................................-0.3V to +80V
VD...........................................................................-0.3V to +12V
FB
MAX5033A/MAX5033B/MAX5033C...................-0.3V to +15V
MAX5033D.........................................................-0.3V to +12V
VOUT Short-Circuit Duration (VIN ≤ 40V).....................Indefinite
VD Short-Circuit Duration..............................................Indefinite
Continuous Power Dissipation (TA = +70°C)
8-Pin PDIP (derate 9.1mW/°C above +70°C)..............727mW
8-Pin SO (derate 5.9mW/°C above +70°C)..................471mW
Operating Temperature Range
MAX5033_U_ _...................................................0°C to +85°C
MAX5033_A_ _..............................................-40°C to +125°C
Storage Temperature Range.............................-65°C to +150°C
Junction Temperature.......................................................+150°C
Lead Temperature (soldering, 10s)...................................+300°C
Soldering Temperature (reflow)
SO, PDIP Lead(Pb)-free...............................................+260°C
SO, PDIP Containing lead (Pb)....................................+240°C
(VIN = +12V, VON/OFF = +12V, IOUT = 0, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C. See the
Typical Operating Circuit.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Voltage Range VIN
MAX5033A 7.5 76.0
V
MAX5033B 7.5 76.0
MAX5033C 15 76
MAX5033D 7.5 76.0
Undervoltage Lockout UVLO 5.2 V
Output Voltage VOUT
MAX5033A, VIN = 7.5V to 76V,
IOUT = 20mA to 500mA 3.185 3.3 3.415
V
MAX5033B, VIN = 7.5V to 76V,
IOUT = 20mA to 500mA 4.85 5.0 5.15
MAX5033C, VIN = 15V to 76V,
IOUT = 20mA to 500mA 11.64 12 12.36
Feedback Voltage VFB VIN = 7.5V to 76V, MAX5033D 1.192 1.221 1.250 V
Efciency η
VIN = 12V, ILOAD = 500mA, MAX5033A 86
%
VIN = 12V, ILOAD = 500mA, MAX5033B 90
VIN = 24V, ILOAD = 500mA, MAX5033C 94
VIN = 12V, VOUT = 5V, ILOAD = 500mA,
MAX5033D 90
Quiescent Supply Current IQ
VFB = 3.5V, VIN = 7.5V to 76V, MAX5033A 270 440
µA
VFB = 5.5V, VIN = 7.5V to 76V, MAX5033B 270 440
VFB = 13V, VIN = 15V to 76V, MAX5033C 270 440
VFB = 1.3V, MAX5033D 270 440
Shutdown Current ISHDN VON/OFF = 0V, VIN = 7.5V to 76V 10 45 µA
Peak Switch Current Limit ILIM (Note 1) 0.95 1.5 2.1 A
Switch Leakage Current IOL VIN = 76V, VON/OFF = 0V, VLX = 0V 1 µA
MAX5033 500mA, 76V, High-Efciency, MAXPower
Step-Down DC-DC Converter
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Absolute Maximum Ratings
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.
Electrical Characteristics (MAX5033_U_ _)
(VIN = +12V, VON/OFF = +12V, IOUT = 0, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the
Typical Operating Circuit.) (Note 2)
(VIN = +12V, VON/OFF = +12V, IOUT = 0, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C. See the
Typical Operating Circuit.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Switch On-Resistance RDS(ON) ISWITCH = 500mA 0.4 0.80 Ω
PFM Threshold IPFM Minimum switch current in any cycle 35 65 95 mA
FB Input Bias Current IBMAX5033D -150 +0.01 +150 nA
ON/OFF CONTROL INPUT
ON/OFF Input-Voltage Threshold VON/OFF Rising trip point 1.53 1.69 1.85 V
ON/OFF Input-Voltage Hysteresis VHYST 100 mV
ON/OFF Input Current ION/OFF VON/OFF = 0V to VIN 10 150 nA
ON/OFF Operating Voltage Range VON/OFF 76 V
OSCILLATOR
Oscillator Frequency fOSC 109 125 135 kHz
Maximum Duty Cycle DMAX MAX5033D 95 %
VOLTAGE REGULATOR
Regulator Output Voltage VD VIN = 8.5V to 76V, IL = 0mA 6.9 7.8 8.8 V
Dropout Voltage 7.5V ≤ VIN ≤ 8.5V, IL = 1mA 2.0 V
Load Regulation ΔVD/ΔIVD 0 to 5mA 150 Ω
PACKAGE THERMAL CHARACTERISTICS
Thermal Resistance
(Junction to Ambient) θJA
SO package (JEDEC 51) 170 °C/W
DIP package (JEDEC 51) 110
THERMAL SHUTDOWN
Thermal-Shutdown Junction
Temperature TSH +160 °C
Thermal-Shutdown Hysteresis THYST 20 °C
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Voltage Range VIN
MAX5033A 7.5 76.0
V
MAX5033B 7.5 76.0
MAX5033C 15 76
MAX5033D 7.5 76.0
Undervoltage Lockout UVLO 5.2 V
Output Voltage VOUT
MAX5033A, VIN = 7.5V to 76V,
IOUT = 20mA to 500mA 3.185 3.3 3.415
V
MAX5033B, VIN = 7.5V to 76V,
IOUT = 20mA to 500mA 4.825 5.0 5.175
MAX5033C, VIN = 15V to 76V,
IOUT = 20mA to 500mA 11.58 12 12.42
MAX5033 500mA, 76V, High-Efciency, MAXPower
Step-Down DC-DC Converter
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Electrical Characteristics (MAX5033_A_ _)
Electrical Characteristics (MAX5033_U_ _) (continued)
(VIN = +12V, VON/OFF = +12V, IOUT = 0, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the
Typical Operating Circuit.) (Note 2)
Note 1: Switch current at which the current limit is activated.
Note 2: All limits at -40°C are guaranteed by design, not production tested.
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Feedback Voltage VFB VIN = 7.5V to 76V, MAX5033D 1.192 1.221 1.250 V
Efciency η
VIN = 12V, ILOAD = 500mA, MAX5033A 86
%
VIN = 12V, ILOAD = 500mA, MAX5033B 90
VIN = 24V, ILOAD = 500mA, MAX5033C 94
VIN = 12V, VOUT = 5V, ILOAD = 500mA,
MAX5033D 90
Quiescent Supply Current IQ
VFB = 3.5V, VIN = 7.5V to 76V, MAX5033A 270 440
µA
VFB = 5.5V, VIN = 7.5V to 76V, MAX5033B 270 440
VFB = 13V, VIN = 15V to 76V, MAX5033C 270 440
VFB = 1.3V, MAX5033D 270 440
Shutdown Current ISHDN VON/OFF = 0V, VIN = 7.5V to 76V 10 45 µA
Peak Switch Current Limit ILIM (Note 1) 0.95 1.5 2.1 A
Switch Leakage Current IOL VIN = 76V, VON/OFF = 0V, VLX = 0V 1 µA
Switch On-Resistance RDS(ON) ISWITCH = 500mA 0.4 0.80 Ω
PFM Threshold IPFM Minimum switch current in any cycle 35 65 110 mA
FB Input Bias Current IBMAX5033D -150 +0.01 +150 nA
ON/OFF CONTROL INPUT
ON/OFF Input-Voltage Threshold VON/OFF Rising trip point 1.50 1.69 1.85 V
ON/OFF Input-Voltage Hysteresis VHYST 100 mV
ON/OFF Input Current ION/OFF VON/OFF = 0V to VIN 10 150 nA
ON/OFF Operating Voltage Range VON/OFF 76 V
OSCILLATOR
Oscillator Frequency fOSC 105 125 137 kHz
Maximum Duty Cycle DMAX MAX5033D 95 %
VOLTAGE REGULATOR
Regulator Output Voltage VD VIN = 8.5V to 76V, IL = 0mA 6.5 7.8 9.0 V
Dropout Voltage 7.5V ≤ VIN ≤ 8.5V, IL = 1mA 2.0 V
Load Regulation ΔVD/ΔIVD 0 to 5mA 150 Ω
PACKAGE THERMAL CHARACTERISTICS
Thermal Resistance
(Junction to Ambient) θJA
SO package (JEDEC 51) 170 °C/W
DIP package (JEDEC 51) 110
THERMAL SHUTDOWN
Thermal-Shutdown Junction
Temperature TSH +160 °C
Thermal-Shutdown Hysteresis THYST 20 °C
MAX5033 500mA, 76V, High-Efciency, MAXPower
Step-Down DC-DC Converter
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Electrical Characteristics (MAX5033_A_ _) (continued)
(VIN = 12V, VON/OFF = 12V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Operating
Circuit, if applicable.)
VOUT vs. TEMPERATURE
(MAX5033BASA, VOUT = 5V)
MAX5033 toc02
TEMPERATURE (C)
V
OUT
(V)
4.95
5.00
5.05
5.10
4.90
IOUT = 0.1A
IOUT = 0.5A
100
500
-50 150
-25 25 75 125
LINE REGULATION
(MAX5033CASA, VOUT = 12V)
MAX5033 toc03
INPUT VOLTAGE (V)
VOUT (V)
50 60 70403020
11.9
12.0
12.1
12.2
12.3
12.4
11.8
10 80
IOUT = 0A
IOUT = 0.5A
LINE REGULATION
(MAX5033BASA, VOUT = 5V)
MAX5033 toc04
INPUT VOLTAGE (V)
V
OUT
(V)
46 56 66362616
4.95
5.00
5.05
5.10
4.90
6 76
IOUT = 0A
IOUT = 0.5A
LOAD REGULATION
(MAX5033CASA, VOUT = 12V)
MAX5033 toc05
ILOAD (mA)
V
OUT
(V)
400300200100
11.9
12.0
12.1
12.2
12.3
12.4
11.8
0 500
VIN = 24V
VIN = 76V
LOAD REGULATION
(MAX5033BASA, VOUT = 5V)
MAX5033 toc06
ILOAD (mA)
VOUT (V)
400300200100
4.95
5.00
5.05
5.10
4.90
0 500
VIN = 7.5V, 24V
VIN = 76V
EFFICIENCY vs. LOAD CURRENT
(MAX5033BASA, VOUT = 5V)
MAX5033 toc07
LOAD CURRENT (mA)
EFFICIENCY (%)
400300200100
30
50
40
20
10
70
60
100
90
80
0
0 500
VIN = 7.5V
VIN = 12V
VIN = 24V
VIN = 48V
VIN = 76V
VOUT vs. TEMPERATURE
(MAX5033CASA, VOUT = 12V)
MAX5033 toc01
TEMPERATURE (C)
V
OUT
(V)
11.9
12.0
12.1
12.2
12.3
12.4
11.8
100
50
0-50 150
-25 25 75 125
IOUT = 0.1A
IOUT = 0.5A
EFFICIENCY vs. LOAD CURRENT
(MAX5033CASA, VOUT = 12V)
MAX5033 toc08
LOAD CURRENT (mA)
EFFICIENCY (%)
400300200100
30
50
40
20
10
70
60
100
90
80
0
0 500
VIN = 15V
VIN = 24V
VIN = 48V
VIN = 76V
OUTPUT CURRENT LIMIT
vs. TEMPERATURE
MAX5033 toc09
TEMPERATURE (°C)
OUTPUT CURRENT LIMIT (A)
0.8
1.1
1.4
1.7
2.0
0.5
MAX5033BASA
5% DROP IN VOUT
100
50
0-50 150
-25 25 75 125
MAX5033 500mA, 76V, High-Efciency, MAXPower
Step-Down DC-DC Converter
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Typical Operating Characteristics
(VIN = 12V, VON/OFF = 12V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Operating
Circuit, if applicable.)
OUTPUT CURRENT LIMIT
vs. INPUT VOLTAGE
MAX5033 toc10
INPUT VOLTAGE (V)
OUTPUT CURRENT LIMIT (A)
665646362616
0.8
1.1
1.4
1.7
2.0
0.5
6 76
MAX5033BASA
VOUT = 5V
5% DROP IN VOUT
QUIESCENT SUPPLY CURRENT
vs. TEMPERATURE
MAX5033 toc11
TEMPERATURE (°C)
QUIESCENT SUPPLY CURRENT (µA)
240
280
320
360
400
200
100
50
0-50 150
-25 25 75 125
QUIESCENT SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX5033 toc12
INPUT VOLTAGE (V)
QUIESCENT SUPPLY CURRENT (µA)
230
260
290
320
350
200
66
46
266 16 36 56 76
SHUTDOWN CURRENT
vs. TEMPERATURE
MAX5033 toc13
TEMPERATURE (C)
SHUTDOWN CURRENT (µA)
5
10
15
20
25
0
100
50
0-50 150
-25 25 75 125
SHUTDOWN CURRENT
vs. INPUT VOLTAGE
MAX5033 toc14
INPUT VOLTAGE (V)
SHUTDOWN CURRENT (µA)
5
10
15
20
25
0
66
46
266 16 36 56 76
OUTPUT VOLTAGE
vs. INPUT VOLTAGE
MAX5033 toc15
VIN (V)
VOUT (V)
12963
3
6
9
12
15
0
0 15
MAX5033CASA
VOUT = 12V
VON/OFF = VIN
IOUT = 0.3A
IOUT = 0.5A
MAX5033BASA
LOAD-TRANSIENT RESPONSE
MAX5033 toc16
400µs/div
B
A
A: VOUT, 200mV/div, AC-COUPLED
B: IOUT, 500mA/div, 100mA TO 500mA
VOUT = 5V
MAX5033BASA
LOAD-TRANSIENT RESPONSE
MAX5033 toc17
400µs/div
B
A
A: VOUT, 100mV/div, AC-COUPLED
B: IOUT, 200mA/div, 100mA TO 250mA
VOUT = 5V
MAX5033BASA
LOAD-TRANSIENT RESPONSE
MAX5033 toc18
400µs/div
B
A
A: VOUT, 100mV/div, AC-COUPLED
B: IOUT, 500mA/div, 250mA TO 500mA
VOUT = 5V
MAX5033 500mA, 76V, High-Efciency, MAXPower
Step-Down DC-DC Converter
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Typical Operating Characteristics (continued)
(VIN = 12V, VON/OFF = 12V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Operating
Circuit, if applicable.)
MAX5033BASA LX WAVEFORMS
MAX5033 toc19
4ms/div
B
0
A
A: SWITCH VOLTAGE (LX PIN) 20V/div, VIN = 48V
B: INDUCTOR CURRENT, 200mA/div, (IOUT = 500mA)
MAX5033BASA LX WAVEFORMS
MAX5033 toc20
4µs/div
B
0
A
0
A: SWITCH VOLTAGE, 20V/div, VIN = 48V
B: INDUCTOR CURRENT, 100mA/div (IOUT = 30mA)
MAX5033BASA LX WAVEFORMS
MAX5033 toc21
4µs/div
B
A
A: SWITCH VOLTAGE (LX PIN), 20V/div, VIN = 48V
B: INDUCTOR CURRENT, 100mA/div (IOUT = 0)
0
0
MAX5033BASA STARTUP WAVEFORM
(IO = 0)
MAX5033 toc22
1ms/div
B
A
A: VON/OFF, 2V/div
B: VOUT, 2V/div
MAX5033BASA STARTUP WAVEFORM
(IO = 0.5A)
MAX5033 toc23
1ms/div
B
A
A: VON/OFF, 2V/div
B: VOUT, 2V/div
PEAK SWITCH CURRENT LIMIT
vs. INPUT VOLTAGE
MAX5033 toc24
INPUT VOLTAGE (V)
PEAK SWITCH CURRENT LIMIT (A)
56 6646362616
0.8
1.1
1.4
1.7
2.0
0.5
6 76
MAX5033BASA
VOUT = 5V
5% DROP IN VOUT
MAX5033 500mA, 76V, High-Efciency, MAXPower
Step-Down DC-DC Converter
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Typical Operating Characteristics (continued)
PIN NAME FUNCTION
1 BST Boost Capacitor Connection. Connect a 0.1μF ceramic capacitor from BST to LX.
2 VD Internal Regulator Output. Bypass VD to GND with a 0.1μF ceramic capacitor.
3SGND Internal Connection. SGND must be connected to GND.
4 FB
Output Sense Feedback Connection. For xed output voltage (MAX5033A, MAX5033B, MAX5033C),
connect FB to VOUT. For adjustable output voltage (MAX5033D), use an external resistive voltage-
divider to set VOUT. VFB regulating set point is 1.22V.
5ON/OFF Shutdown Control Input. Pull ON/OFF low to put the device in shutdown mode. Drive ON/OFF high
for normal operation.
6GND Ground.
7 VIN Input Voltage. Bypass VIN to GND with a low-ESR capacitor as close to the device as possible.
8LX Source Connection of Internal High-Side Switch.
ENABLE
LX
BST
VIN
ON/OFF
VREF
REGULATOR
(FOR DRIVER)
REGULATOR
(FOR ANALOG)
OSC
RAMP
HIGH-SIDE
CURRENT
SENSE
IREF-PFM
IREF-LIM
CPFM
1.69V
CILIM
FB
x1
VREF EAMP
CONTROL
LOGIC
CPWM
VD
GND
Rh
Rl
CLK
SGND
MAX5033
TYPE 3
COMPENSATION THERMAL
SHUTDOWN
RAMP
MAX5033 500mA, 76V, High-Efciency, MAXPower
Step-Down DC-DC Converter
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Pin Description
Simplied Block Diagram
Detailed Description
The MAX5033 step-down DC-DC converter operates
from a 7.5V to 76V input voltage range. A unique volt-
age- mode control scheme with voltage feed-forward
and an internal switching DMOS FET provides high
efficiency over a wide input voltage range. This pulse-
width modulated converter operates at a fixed 125kHz
switching frequency. The device also features automatic
pulse-skipping mode to provide low quiescent current and
high efficiency at light loads. Under no load, the MAX5033
consumes only 270μA, and in shutdown mode, consumes
only 10μA. The MAX5033 also features undervoltage
lockout, hiccup-mode output shortcircuit protection, and
thermal shutdown.
Shutdown Mode
Drive ON/OFF to ground to shut down the MAX5033.
Shutdown forces the internal power MOSFET off, turns
off all internal circuitry, and reduces the VIN supply cur-
rent to 10μA (typ). The ON/OFF rising threshold is 1.69V
(typ). Before any operation begins, the voltage at ON/OFF
must exceed 1.69V (typ). The ON/OFF input has 100mV
hysteresis.
Undervoltage Lockout (UVLO)
Use the ON/OFF function to program the UVLO threshold
at the input. Connect a resistive voltage-divider from VIN
to GND with the center node to ON/OFF as shown in
Figure 1. Calculate the threshold value by using the fol-
lowing formula:
UVLO(TH) R1
V 1 1.85V
R2

=+×


The minimum recommended VUVLO(TH) is 6.5V, 7.5V,
and 13V for the output voltages of 3.3V, 5V, and 12V,
respectively. The recommended value for R2 is less than
1MΩ.
If the external UVLO threshold-setting divider is not used,
an internal undervoltage-lockout feature monitors the
supply voltage at VIN and allows operation to start when
VIN rises above 5.2V (typ). This feature can be used only
when VIN rise time is faster than 2ms. For slower VIN rise
time, use the resistive divider at ON/OFF.
Boost High-Side Gate Drive (BST)
Connect a flying bootstrap capacitor between LX and
BST to provide the gate-drive voltage to the high-side
n-channel DMOS switch. The capacitor is alternately
charged from the internally regulated output-voltage
VD and placed across the high-side DMOS driver. Use
a 0.1μF, 16V ceramic capacitor located as close to the
device as possible.
On startup, an internal low-side switch connects LX to
ground and charges the BST capacitor to VD. Once the
BST capacitor is charged, the internal low-side switch is
turned off and the BST capacitor voltage provides the
necessary enhancement voltage to turn on the high-side
switch.
Thermal-Overload Protection
The MAX5033 features integrated thermal-overload pro-
tection. Thermal-overload protection limits total power dis-
sipation in the device, and protects the device in the event
of a fault condition. When the die temperature exceeds
+160°C, an internal thermal sensor signals the shutdown
logic, turning off the internal power MOSFET and allow-
ing the IC to cool. The thermal sensor turns the internal
power MOSFET back on after the IC’s die temperature
cools down to +140°C, resulting in a pulsed output under
continuous thermaloverload conditions.
Applications Information
Setting the Output Voltage
The MAX5033A/B/C have preset output voltages of 3.3V,
5.0V, and 12V, respectively. Connect FB to the preset
output voltage (see the Typical Operating Circuit).
The MAX5033D offers an adjustable output voltage. Set
the output voltage with a resistive voltage-divider connect-
ed from the circuit’s output to ground (Figure 1). Connect
the center node of the divider to FB. Choose R4 less than
15kΩ, then calculate R3 as follows:
OUT
(V 1.22)
R3 R4
1.22
−
= ×
Figure 1. Adjustable Output Voltage
MAX5033D
GND
BST
LX
VIN
SGND
FB
D1
50SQ100
VD
220µH
VOUT
5V, 0.5A
VIN
7.5V TO 76V
47µF
0.1µF
0.1µF
COUT
33µF
R1
R2 R3
41.2kΩ
R4
13.3kΩ
ON/OFF
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The MAX5033 features internal compensation for opti-
mum closed-loop bandwidth and phase margin. With the
preset compensation, it is strongly advised to sense the
output immediately after the primary LC.
Inductor Selection
The choice of an inductor is guided by the voltage differ-
ence between VIN and VOUT, the required output current,
and the operating frequency of the circuit. Use an inductor
with a minimum value given by:
IN OUT
OUTMAX SW
(V V ) D
L0.3 I f
−×
=××
where: D = VOUT/VIN, IOUTMAX is the maximum output
current required, and fSW is the operating frequency of
125kHz. Use an inductor with a maximum saturation cur-
rent rating equal to at least the peak switch current limit
(ILIM). Use inductors with low DC resistance for higher
efficiency.
Selecting a Rectier
The MAX5033 requires an external Schottky rectifier
as a freewheeling diode. Connect this rectifier close to
the device using short leads and short PC board traces.
Choose a rectifier with a continuous current rating greater
than the highest expected output current. Use a rectifier
with a voltage rating greater than the maximum expected
input voltage, VIN. Use a low forward-voltage Schottky
rectifier for proper operation and high efficiency. Avoid
higher than necessary reverse-voltage Schottky rectifiers
that have higher forward-voltage drops. Use a Schottky
rectifier with forward-voltage drop (VFB) less than 0.45V
at +25°C and maximum load current to avoid forward
biasing of the internal body diode (LX to ground). Internal
body-diode conduction may cause excessive junction
temperature rise and thermal shutdown. Use Table 1 to
choose the proper rectifier at different input voltages and
output current.
Input Bypass Capacitor
The discontinuous input-current waveform of the buck
converter causes large ripple currents in the input capaci-
tor. 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 MAX5033 high switching frequency allows the use of
smaller-value input capacitors.
The input ripple is comprised of ΔVQ (caused by the
capacitor discharge) and ΔVESR (caused by the ESR
of the capacitor). Use low-ESR aluminum electrolytic
capacitors with high ripple-current capability at the input.
Assuming that the contribution from the ESR and capaci-
tor discharge is equal to 90% and 10%, respectively,
calculate the input capacitance and the ESR required for
a specified ripple using the following equations:
ESR
IN L
OUT
OUT
IN Q SW
IN OUT OUT
LIN SW
OUT
V
ESR I
I2
I D(1 D)
C Vf
where :
(V V ) V
I Vf L
V
D
∆
=∆

+


×−
=∆×
−×
∆= ××
=
IN
V
IOUT is the maximum output current of the converter and
fSW is the oscillator switching frequency (125kHz). For
example, at VIN = 48V and VOUT = 3.3V, the ESR and
input capacitance are calculated for the input peak-topeak
ripple of 100mV or less, yielding an ESR and capacitance
value of 130mΩ and 27μF, respectively.
Low-ESR, ceramic, multilayer chip capacitors are rec-
ommended for size-optimized application. For ceramic
capacitors, assume the contribution from ESR and capac-
itor discharge is equal to 10% and 90%, respectively.
The input capacitor must handle the RMS ripple current
without significant rise in temperature. The maximum
capacitor RMS current occurs at about 50% duty cycle.
Table 1. Diode Selection
VIN (V) DIODE PART NUMBER MANUFACTURER
7.5 to
36
15MQ040N IR
B240A Diodes Incorporated
B240 Central Semiconductor
MBRS240, MBRS1540 ON Semiconductor
7.5 to
56
30BQ060 IR
B360A Diodes Incorporated
CMSH3-60 Central Semiconductor
MBRD360, MBR3060 ON Semiconductor
7.5 to
76
50SQ100, 50SQ80 IR
MBRM5100 Diodes Incorporated
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Ensure that the ripple specification of the input capacitor
exceeds the worst-case capacitor RMS ripple current.
Use the following equations to calculate the input capaci-
tor RMS current:
22
CRMS PRMS AVGIN
I I I= −
where :
( )
()
22
PRMS PK DC PK DC
OUT OUT
AVGIN IN
LL
PK OUT DC OUT
OUT
IN
D
I I I I I 3
VI
IV
II
I I , I I
22
V
and D V
= + +× ×
×
=×η
∆∆
=+=−
=
IPRMS is the input switch RMS current, IAVGIN is the input
average current, and η is the converter efficiency.
The ESR of aluminum electrolytic capacitors increases
significantly at cold temperatures. Use a 1μF or greater
value ceramic capacitor in parallel with the aluminum
electrolytic input capacitor, especially for input voltages
below 8V.
Output Filter Capacitor
The worst-case peak-to-peak and RMS capacitor ripple
current, allowable peak-to-peak output ripple voltage, and
the maximum deviation of the output voltage during load
steps determine the capacitance and the ESR require-
ments for the output capacitors.
The output capacitance and its ESR form a zero, which
improves the closed-loop stability of the buck regulator.
Choose the output capacitor so the ESR zero frequency
(fZ) occurs between 20kHz to 40kHz. Use the following
equation to verify the value of fZ. Capacitors with 100mΩ
to 250mΩ ESR are recommended to ensure the closed-
loop stability while keeping the output ripple low.
ZOUT OUT
1
f2 C ESR
=×π× ×
The output ripple is comprised of ΔVOQ (caused by the
capacitor discharge) and ΔVOESR (caused by the ESR
of the capacitor). Use low-ESR tantalum or aluminum
electrolytic capacitors at the output. Assuming that the
contributions from the ESR and capacitor discharge equal
80% and 20%, respectively, calculate the output capaci-
tance and the ESR required for a specified ripple using
the following equations:
OESR
OUT L
L
OUT OQ SW
V
ESR I
I
C2.2 V f
∆
=∆
∆
≈×∆ ×
The MAX5033 has an internal soft-start time (tSS) of
400μs. It is important to keep the output rise time at
startup below tSS to avoid output overshoot. The output
rise time is directly proportional to the output capacitor.
Use 68μF or lower capacitance at the output to control the
overshoot below 5%.
In a dynamic load application, the allowable deviation of
the output voltage during the fast-transient load dictates
the output capacitance value and the ESR. The output
capacitors supply the step load current until the controller
responds with a greater duty cycle. The response time
(tRESPONSE) depends on the closedloop bandwidth of
the converter. The resistive drop across the capacitor
ESR and capacitor discharge cause a voltage droop dur-
ing a step load. Use a combination of low-ESR tantalum
and ceramic capacitors for better transient load and
ripple/noise performance. Keep the maximum output-
voltage deviation above the tolerable limits of the elec-
tronics being powered. Assuming a 50% contribution from
the output capacitance discharge and the ESR drop, use
the following equations to calculate the required ESR and
capacitance value:
OESR
OUT STEP
STEP RESPONSE
OUT OQ
V
ESR I
It
CV
∆
=
×
=∆
where ISTEP is the load step and tRESPONSE is the
response time of the controller. Controller response time
is approximately one-third of the reciprocal of the closed-
loop unity-gain bandwidth, 20kHz (typ).
PCB Layout Considerations
Proper PCB layout is essential. Minimize ground noise
by connecting the anode of the Schottky rectifier, the
input bypass-capacitor ground lead, and the output
filter-capacitor ground lead to a single point (star-ground
configuration). A ground plane is required. Minimize lead
lengths to reduce stray capacitance, trace resistance, and
radiated noise. In particular, place the Schottky rectifier
diode right next to the device. Also, place BST and VD
bypass capacitors very close to the device. Use the PCB
copper plane connecting to VIN and LX for heatsinking.
MAX5033 500mA, 76V, High-Efciency, MAXPower
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Figure 2. Fixed Output Voltages
Table 2. Typical External Components Selection (Circuit of Figure 2)
VIN (V) VOUT (V) IOUT (A) EXTERNAL COMPONENTS
7.5 to 76 3.3 0.5
CIN = 47μF, Panasonic, EEVFK2A470Q
COUT = 47μF, Vishay Sprague, 594D476X_016C2T
CBST = 0.1μF, 0805
R1 = 1MΩ ±1%, 0805
R2 = 384kΩ ±1%, 0805
D1 = 50SQ100, IR
L1 = 150μH, Coilcraft Inc., DO5022P-154
7.5 to 76 5 0.5
CIN = 47μF, Panasonic, EEVFK2A470Q
COUT = 33μF, Vishay Sprague, 594D336X_016C2T
CBST = 0.1μF, 0805
R1 = 1MΩ ±1%, 0805
R2 = 384kΩ ±1%, 0805
D1 = 50SQ100, IR
L1 = 220μH, Coilcraft Inc., DO5022P-224
15 to 76 12 0.5
CIN = 47μF, Panasonic, EEVFK2A470Q
COUT = 15μF, Vishay Sprague, 594D156X_025C2T
CBST = 0.1μF, 0805
R1 = 1MΩ ±1%, 0805
R2 = 384kΩ ±1%, 0805
D1 = 50SQ100, IR
L1 = 330μH, Coilcraft Inc., DO5022P-334
MAX5033
GND
BST
LX
VIN
SGND
FB
D1
VD
L1
VOUT
VIN
CIN
0.1µF
0.1µF
COUT
R1
R2
ON/OFF
MAX5033 500mA, 76V, High-Efciency, MAXPower
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Application Circuit
Table 2. Typical External Components Selection (Circuit of Figure 2) (continued)
VIN (V) VOUT (V) IOUT (A) EXTERNAL COMPONENTS
9 to 14
3.3 0.5
CIN = 100μF, Panasonic, EEVFK1E101P
COUT = 47μF, Vishay Sprague, 594D476X_016C2T
CBST = 0.1μF, 0805
R1 = 1MΩ ±1%, 0805
R2 = 274kΩ ±1%, 0805
D1 = B220/A, Diodes Incorporated
L1 = 150μH, Coilcraft Inc., DO5022P-154
5 0.5
CIN = 100μF, Panasonic, EEVFK1E101P
COUT = 33μF, Vishay Sprague, 594D336X_016C2T
CBST = 0.1μF, 0805
R1 = 1MΩ ±1%, 0805
R2 = 274kΩ ±1%, 0805
D1 = B220/A, Diodes Incorporated
L1 = 220μH, Coilcraft Inc., DO5022P-224
18 to 36
3.3 0.5
CIN = 100μF, Panasonic, EEVFK1H101P
COUT = 47μF, Vishay Sprague, 594D476X_016C2T
CBST = 0.1μF, 0805
R1 = 1MΩ ±1%, 0805
R2 = 130kΩ ±1%, 0805
D1 = B240/A, Diodes Incorporated
L1 = 150μH, Coilcraft Inc., DO5022P-154
5 0.5
CIN = 100μF, Panasonic, EEVFK1H101P
COUT = 33μF, Vishay Sprague, 594D336X_016C2T
CBST = 0.1μF, 0805
R1 = 1MΩ ±1%, 0805
R2 = 130kΩ ±1%, 0805
D1 = B240/A, Diodes Incorporated
L1 = 220μH, Coilcraft Inc., DO5022P-224
12 0.5
CIN = 100μF, Panasonic, EEVFK1H101P
COUT = 15μF, Vishay Sprague, 594D156X_025C2T
CBST = 0.1μF, 0805
R1 = 1MΩ ±1%, 0805
R2 = 130kΩ ±1%, 0805
D1 = B240/A, Diodes Incorporated
L1 = 330μH, Coilcraft Inc., DO5022P-334
MAX5033 500mA, 76V, High-Efciency, MAXPower
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Table 3. Component Suppliers
Figure 3. Load Temperature Monitoring with ON/OFF (Requires Accurate VIN)
SUPPLIER PHONE FAX WEBSITE
AVX 843-946-0238 843-626-3123 www.avxcorp.com
Coilcraft 847-639-6400 847-639-1469 www.coilcraft.com
Diodes Incorporated 805-446-4800 805-446-4850 www.diodes.com
Nichicon 858-824-1515 858-824-1525 www.nichicon.com
Panasonic 714-373-7366 714-737-7323 www.panasonic.com
SANYO 619-661-6835 619-661-1055 www.sanyo.com
TDK 847-803-6100 847-390-4405 www.component.tdk.com
Vishay 402-563-6866 402-563-6296 www.vishay.com
MAX5033
CIN
47µF
COUT
33µF
L1
220µH
FB
VOUT
5V AT 0.5A
BST
LX
SGND
0.1µF
0.1µF
GND
VIN
12V VIN
PTC*
Rt
Ct D1
B240
VD
*LOCATE PTC AS CLOSE TO HEAT-DISSIPATING COMPONENTS AS POSSIBLE.
ON/OFF
MAX5033 500mA, 76V, High-Efciency, MAXPower
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Figure 4. Dual-Sequenced DC-DC Converters (Startup Delay Determined by R1/R1’, Ct/Ct’ and Rt/Rt’)
MAX5033B
CIN
47µF
COUT
68µF
L1
220µH
FB
VOUT
5V AT 0.5A
BST
LX
SGND
0.1µF
0.1µF
GND
VIN
7.5V TO 36V VIN
R1
Rt
Ct D1
B240
VD
ON/OFF
MAX5033A
C'IN
68µF
C'OUT
68µF
L1'
150µH
FB
V'OUT
3.3V AT 0.5A
BST
LX
SGND
0.1µF
0.1µF
GND
VIN
R1'
Rt'
Ct' D1'
B240
VD
ON/OFF
MAX5033 500mA, 76V, High-Efciency, MAXPower
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Chip Information
PROCESS: BiCMOS
PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
8 PDIP P8+3 21-0043 —
8 SO S8+5 21-0041 90-0096
MAX5033 500mA, 76V, High-Efciency, MAXPower
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Package Information
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.
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 9/03 Initial release —
1 5/04 New product update 1–7, 10
2 6/04 Removed future product asterisk and made specication changes 1, 2, 3
3 1/07 Modied Absolute Maximum Ratings specications 2
4 4/10 Corrected inconsistencies in Absolute Maximum Ratings and Electrical
Characteristics table 1, 2, 3, 4, 17
5 4/14 No /V OPNs; removed Automotive reference in Applications section 1
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 specications 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.
MAX5033 500mA, 76V, High-Efciency, MAXPower
Step-Down DC-DC Converter
© 2014 Maxim Integrated Products, Inc.
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Revision History
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