MAX5035AUSA+ [MAXIM]
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19-2988; Rev 3; 5/09
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
MAX035
General Description
Features
The MAX5035 easy-to-use, high-efficiency, high-volt-
age, step-down DC-DC converter operates from an
input voltage up to 76V and consumes only 270µA qui-
escent current at no load. This pulse-width modulated
(PWM) converter operates at a fixed 125kHz switching
frequency at heavy loads, and automatically switches
to pulse-skipping mode to provide low quiescent cur-
rent and high efficiency at light loads. The MAX5035
includes internal frequency compensation simplifying
circuit implementation. The device uses an internal low-
on-resistance, 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 protec-
tion, and thermal shutdown.
♦ Wide 7.5V to 76V Input Voltage Range
♦ Fixed (3.3V, 5V, 12V) and Adjustable
(1.25V to 13.2V) Versions
♦ 1A 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
The MAX5035 delivers up to 1A output current. The out-
put current may be limited by the maximum power dis-
sipation capability of the package. External shutdown is
included, featuring 10µA (typ) shutdown current. The
MAX5035A/B/C versions have fixed output voltages of
3.3V, 5V, and 12V, respectively, while the MAX5035D
features an adjustable output voltage from 1.25V to
13.2V.
Limit
♦ 8-Pin SO and PDIP Packages
Ordering Information
OUTPUT
VOLTAGE
(V)
PIN-
PACKAGE
PART
TEMP RANGE
MAX5035AUSA
MAX5035AUPA
MAX5035AASA
0°C to +85°C
0°C to +85°C
8 SO
The MAX5035 is available in space-saving 8-pin SO
and 8-pin plastic DIP packages and operates over the
automotive (-40°C to +125°C) temperature range.
8 PDIP
3.3
5.0
-40°C to +125°C 8 SO
MAX5035AASA/V+ -40°C to +125°C 8 SO
Applications
MAX5035BUSA
MAX5035BUPA
MAX5035BASA
0°C to +85°C
0°C to +85°C
8 SO
8 PDIP
Automotive
-40°C to +125°C 8 SO
Consumer Electronics
Industrial
MAX5035BASA/V+ -40°C to +125°C 8 SO
+Denotes lead(Pb)-free/RoHS-compliant package.
Ordering Information continued at end of data sheet.
Distributed Power
Typical Operating Circuit
Pin Configuration
V
IN
7.5V TO 76V
TOP VIEW
V
IN
68μF
BST
LX
0.1μF
100μH
MAX5035
V
5V
OUT
BST
VD
1
2
3
4
8
7
6
5
LX
R1
R2
D1
50SQ100
V
IN
MAX5035
ON/OFF
68μF
SGND
FB
GND
ON
FB
ON/OFF
VD
OFF
SGND
GND
0.1μF
SO/PDIP
________________________________________________________________ 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.
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
ABSOLUTE MAXIMUM RATINGS
(Voltages referenced to GND, unless otherwise specified.)
V Short-Circuit Duration (V ≤ 40V)........................Indefinite
IN
OUT
V
.........................................................................-0.3V to +80V
VD Short-Circuit Duration ..............................................Indefinite
IN
SGND ....................................................................-0.3V to +0.3V
LX.................................................................-0.8V to (V + 0.3V)
BST ...............................................................-0.3V to (V + 10V)
Continuous Power Dissipation (T = +70°C)
A
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
IN
IN
IN
BST (transient < 100ns)................................-0.3V to (V + 15V)
BST to LX................................................................-0.3V to +10V
BST to LX (transient < 100ns) ................................-0.3V to +15V
MAX5035_U_ _ ...................................................0°C to +85°C
MAX5035_A_ _ ..............................................-40°C to +125°C
Storage Temperature Range.............................-65°C to +150°C
Junction Temperature......................................................+150°C
Lead Temperature (soldering, 10s) .................................+300°C
ON/OFF........................................................-0.3V to (V + 0.3V)
IN
MAX035
VD...........................................................................-0.3V to +12V
FB
MAX5035A/MAX5035B/MAX5035C ...................-0.3V to +15V
MAX5035D .........................................................-0.3V to +12V
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 (MAX5035_U_ _)
(V = +12V, V
= +12V, I
= 0, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C. See the
IN
ON/OFF
OUT
A
A
Typical Application Circuit.)
PARAMETER
SYMBOL
CONDITIONS
MIN
7.5
7.5
15
TYP
MAX
76.0
76.0
76
UNITS
MAX5035A
MAX5035B
MAX5035C
MAX5035D
Input Voltage Range
Undervoltage Lockout
V
V
V
IN
7.5
76.0
UVLO
5.2
3.3
V
= 7.5V to 76V,
IN
MAX5035A
MAX5035B
MAX5035C
3.185
4.85
3.415
5.15
I
= 20mA to 1A
OUT
V
= 7.5V to 76V,
IN
Output Voltage
V
5.0
12
V
OUT
I
= 20mA to 1A
= 15V to 76V,
OUT
V
IN
11.64
1.192
12.36
1.250
I
= 20mA to 1A
OUT
Feedback Voltage
Efficiency
V
V
V
V
V
= 7.5V to 76V, MAX5035D
1.221
86
V
FB
IN
IN
IN
IN
= 12V, I
= 12V, I
= 24V, I
= 0.5A, MAX5035A
= 0.5A, MAX5035B
= 0.5A, MAX5035C
LOAD
LOAD
LOAD
90
η
94
%
V
= 12V, V
= 5V, I
= 0.5A,
IN
OUT
LOAD
90
MAX5035D
V
V
V
V
V
= 3.5V, V = 7.5V to 76V, MAX5035A
270
270
270
270
10
440
440
440
440
45
FB
IN
= 5.5V, V = 7.5V to 76V, MAX5035B
FB
IN
Quiescent Supply Current
I
µA
Q
= 13V, V = 15V to 76V, MAX5035C
IN
FB
= 1.3V, MAX5035D
FB
Shutdown Current
I
= 0V, V = 7.5V to 76V
µA
A
SHDN
ON/OFF
IN
Peak Switch Current Limit
Switch Leakage Current
Switch On-Resistance
I
(Note 1)
1.30
1.80
1
2.50
LIM
I
V
= 76V, V
= 0V, V = 0V
µA
Ω
OL
IN
ON/OFF
LX
R
I
= 1A
0.40
0.80
DS(ON)
SWITCH
2
_______________________________________________________________________________________
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
MAX035
ELECTRICAL CHARACTERISTICS (continued) (MAX5035_U_ _)
(V = +12V, V
= +12V, I
= 0, T = 0°C to +85°C, unless otherwise noted. Typical values are at T = +25°C. See the
IN
ON/OFF
OUT
A
A
Typical Application Circuit.)
PARAMETER
PFM Threshold
SYMBOL
CONDITIONS
Minimum switch current in any cycle
MAX5035D
MIN
55
TYP
85
MAX
130
UNITS
mA
I
PFM
FB Input Bias Current
ON/OFF CONTROL INPUT
I
-150
+0.01
+150
nA
B
ON/OFF Input-Voltage Threshold
ON/OFF Input-Voltage Hysteresis
ON/OFF Input Current
OSCILLATOR
V
Rising trip point
1.53
1.69
100
10
1.85
150
135
V
ON/OFF
V
mV
nA
HYST
I
V
= 0V to V
ON/OFF IN
ON/OFF
Oscillator Frequency
Maximum Duty Cycle
VOLTAGE REGULATOR
Regulator Output Voltage
Dropout Voltage
f
109
6.9
125
95
kHz
%
OSC
D
MAX5035D
MAX
VD
V
= 8.5V to 76V, I = 0
7.8
2.0
150
8.8
V
V
IN
L
7.5V ≤ V ≤ 8.5V, I = 1mA
IN
L
Load Regulation
ΔVD/ΔI
0 to 5mA
Ω
VD
PACKAGE THERMAL CHARACTERISTICS
SO package (JEDEC 51)
DIP package (JEDEC 51)
170
110
Thermal Resistance
(Junction to Ambient)
θ
°C/W
JA
THERMAL SHUTDOWN
Thermal-Shutdown Junction
Temperature
T
+160
20
°C
°C
SH
Thermal-Shutdown Hysteresis
T
HYST
ELECTRICAL CHARACTERISTICS (MAX5035_A_ _)
(V = +12V, V
= +12V, I
= 0, T = T = -40°C to +125°C, unless otherwise noted. Typical values are at T = +25°C. See
IN
ON/OFF
OUT
A
J
A
the Typical Application Circuit.) (Note 2)
PARAMETER SYMBOL
CONDITIONS
MIN
7.5
7.5
15
TYP
MAX
76.0
76.0
76
UNITS
MAX5035A
MAX5035B
MAX5035C
MAX5035D
Input Voltage Range
V
V
V
IN
7.5
76.0
Undervoltage Lockout
Output Voltage
UVLO
5.2
3.3
V
= 7.5V to 76V,
IN
MAX5035A
MAX5035B
MAX5035C
3.185
4.825
3.415
5.175
I
= 20mA to 1A
OUT
V
= 7.5V to 76V,
IN
V
V
5.0
OUT
I
= 20mA to 1A
= 15V to 76V,
OUT
V
IN
11.58
1.192
12
12.42
1.250
I
= 20mA to 1A
OUT
Feedback Voltage
V
V
= 7.5V to 76V, MAX5035D
IN
1.221
V
FB
_______________________________________________________________________________________
3
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
ELECTRICAL CHARACTERISTICS (MAX5035_A_ _)
(V = +12V, V
= +12V, I
= 0, T = T = -40°C to +125°C, unless otherwise noted. Typical values are at T = +25°C. See
IN
ON/OFF
OUT
A
J
A
the Typical Application Circuit.) (Note 2)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
86
MAX
UNITS
V
V
V
V
= 12V, I
= 12V, I
= 24V, I
= 0.5A, MAX5035A
= 0.5A, MAX5035B
= 0.5A, MAX5035C
IN
IN
IN
IN
LOAD
LOAD
LOAD
90
Efficiency
η
%
94
MAX035
= 12V, V
= 5V, I
= 0.5A,
OUT
LOAD
90
MAX5035D
V
V
V
V
V
= 3.5V, V = 7.5V to 76V, MAX5035A
270
270
270
270
10
440
440
440
440
45
FB
IN
= 5.5V, V = 7.5V to 76V, MAX5035B
FB
IN
Quiescent Supply Current
I
µA
Q
= 13V, V = 15V to 76V, MAX5035C
IN
FB
= 1.3V, MAX5035D
FB
Shutdown Current
I
= 0V, V = 7.5V to 76V
µA
A
SHDN
ON/OFF
IN
Peak Switch Current Limit
Switch Leakage Current
Switch On-Resistance
PFM Threshold
I
(Note 1)
1.30
1.80
1
2.50
LIM
I
V
= 76V, V
= 0V, V = 0V
µA
Ω
OL
IN
ON/OFF
LX
R
I
= 1A
0.40
85
0.80
130
DS(ON)
SWITCH
I
Minimum switch current in any cycle
MAX5035D
55
mA
nA
PFM
FB Input Bias Current
ON/OFF CONTROL INPUT
ON/OFF Input-Voltage Threshold
ON/OFF Input-Voltage Hysteresis
ON/OFF Input Current
OSCILLATOR
I
-150
+0.01
+150
B
V
Rising trip point
1.50
1.69
100
10
1.85
150
137
V
ON/OFF
V
mV
nA
HYST
I
V
= 0V to V
ON/OFF IN
ON/OFF
Oscillator Frequency
Maximum Duty Cycle
VOLTAGE REGULATOR
Regulator Output Voltage
Dropout Voltage
f
105
6.5
125
95
kHz
%
OSC
D
MAX5035D
= 8.5V to 76V, I = 0
MAX
VD
V
7.8
2.0
150
9.0
V
V
IN
L
7.5V ≤ V ≤ 8.5V, I = 1mA
IN
L
Load Regulation
ΔVD/ΔI
0 to 5mA
Ω
VD
PACKAGE THERMAL CHARACTERISTICS
SO package (JEDEC 51)
DIP package (JEDEC 51)
170
110
Thermal Resistance
(Junction to Ambient)
θ
°C/W
JA
THERMAL SHUTDOWN
Thermal-Shutdown Junction
Temperature
T
+160
20
°C
°C
SH
Thermal-Shutdown Hysteresis
T
HYST
Note 1: Switch current at which current limit is activated.
Note 2: All limits at -40°C are guaranteed by design, not production tested.
4
_______________________________________________________________________________________
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
MAX035
Typical Operating Characteristics
(V = 12V, V
IN
= 12V, T = -40°C to +125°C, unless otherwise noted. Typical values are at T = +25°C. See the Typical
A A
ON/OFF
Application Circuit, if applicable.)
V
vs. TEMPERATURE
V
vs. TEMPERATURE
OUT
OUT
(MAX5035AASA, V
= 3.3V)
(MAX5035DASA, V
= 5V)
OUT
OUT
3.40
3.36
3.32
3.28
5.20
5.15
5.10
5.05
5.00
4.95
4.90
4.85
4.80
3.40
3.36
3.32
3.28
I
= 0.1A
I
= 0.1A
OUT
OUT
I
= 1A
OUT
I
= 1A
OUT
I
= 0.1A
OUT
I
= 1A
OUT
3.24
3.20
3.24
3.20
25
75
125
100
150
-50 -25
0
50
-50 -25
0
25 50 75 100 125 150
TEMPERATURE (°C)
5
20
35
50
65
80
TEMPERATURE (°C)
INPUT VOLTAGE (V)
LOAD REGULATION
(MAX5035AASA, V = 3.3V)
LINE REGULATION
(MAX5035DASA, V
= 5V)
OUT
OUT
5.20
5.15
5.10
5.05
5.00
4.95
4.90
4.85
4.80
3.40
5.10
5.05
5.00
4.95
4.90
V
= 76V
IN
3.36
3.32
3.28
3.24
3.20
V
IN
= 7.5V, 24V
V
IN
= 24V
I
= 0.1A
OUT
V
IN
= 7.5V
I
= 1A
OUT
V
IN
= 76V
400
5
20
35
50
65
80
0
200
400
600
(mA)
800
1000
0
200
600
(mA)
800
1000
INPUT VOLTAGE (V)
I
I
LOAD
LOAD
_______________________________________________________________________________________
5
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
(V = 12V, V
IN
= 12V, T = -40°C to +125°C, unless otherwise noted. Typical values are at T = +25°C. See the Typical
ON/OFF
A
A
Application Circuit, if applicable.)
EFFICIENCY vs. LOAD CURRENT
EFFICIENCY vs. LOAD CURRENT
EFFICIENCY vs. LOAD CURRENT
(MAX5035DASA, V
= 12V)
(MAX5035AASA, V
= 3.3V)
(MAX5035DASA, V
= 5V)
OUT
OUT
OUT
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
MAX035
V
= 15V
IN
V
= 7.5V
V = 7.5V
IN
IN
V
= 24V
IN
V
= 12V
V = 12V
IN
IN
V
= 48V
IN
V
= 24V
V = 24V
IN
IN
V
= 76V
IN
V
= 48V
V = 48V
IN
IN
V
IN
= 76V
V
IN
= 76V
0
200
400
600
800
1000
0
200
400
600
800
1000
0
200
400
600
800
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
OUTPUT CURRENT LIMIT
vs. TEMPERATURE
OUTPUT CURRENT LIMIT
vs. INPUT VOLTAGE
QUIESCENT SUPPLY CURRENT
vs. TEMPERATURE
2.0
1.5
1.0
0.5
0
2.0
350
320
290
260
230
200
1.7
1.4
1.1
0.8
0.5
MAX5035DASA
MAX5035DASA
= 5V
V
OUT
= 5V
V
OUT
5% DROP IN V
OUT
5% DROP IN VOUT
-50 -25
0
25 50 75 100 125 150
25
75
125
100
150
-50 -25
0
50
5
20
35
50 65
80
TEMPERATURE (°C)
INPUT VOLTAGE (V)
TEMPERATURE (°C)
SHUTDOWN CURRENT
vs. TEMPERATURE
QUIESCENT SUPPLY CURRENT
vs. INPUT VOLTAGE
SHUTDOWN CURRENT vs. INPUT VOLTAGE
25
350
320
290
260
230
200
20
16
12
8
20
15
10
5
4
0
0
25
75
125
100
150
-50 -25
0
50
6
16
26
36
46
56
66
76
6
16
26
36
46
56
66
76
TEMPERATURE (°C)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
6
_______________________________________________________________________________________
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
MAX035
Typical Operating Characteristics (continued)
(V = 12V, V
IN
= 12V, T = -40°C to +125°C, unless otherwise noted. Typical values are at T = +25°C. See the Typical
ON/OFF
A
A
Application Circuit, if applicable.)
MAX5035DASA
LOAD-TRANSIENT RESPONSE
OUTPUT VOLTAGE
vs. INPUT VOLTAGE
MAX5035DASA
LOAD-TRANSIENT RESPONSE
MAX5035 toc17
MAX5035 toc18
15
MAX5035DASA
V
= 5V
V
OUT
= 5V
OUT
V
V
= 12V
= V
OUT
/
12
9
ON OFF
IN
A
B
A
B
6
I
= 1A
OUT
3
I
= 0.3A
OUT
I
= 0
9
OUT
0
0
3
6
12
15
400μs/div
400μs/div
V
IN
(V)
A: V , 200mV/div, AC-COUPLED
OUT
A: V , 200mV/div, AC-COUPLED
OUT
B: I , 500mA/div, 0.1A TO 1A
OUT
B: I , 500mA/div, 0.5A TO 1A
OUT
MAX5035DASA
LOAD-TRANSIENT RESPONSE
MAX5035DASA LX WAVEFORMS
MAX5035DASA LX WAVEFORMS
MAX5035 toc20
MAX5035 toc21
MAX5035 toc19
V
= 5V
OUT
A
A
A
0
0
B
0
B
0
B
4μs/div
4μs/div
400μs/div
A: SWITCH VOLTAGE (LX PIN), 20V/div (V = 48V)
IN
A: SWITCH VOLTAGE (LX PIN), 20V/div (V = 48V)
IN
A: V , 200mV/div, AC-COUPLED
OUT
B: I , 500mA/div, 0.1A TO 0.5A
OUT
B: INDUCTOR CURRENT, 500mA/div (I
= 1A)
B: INDUCTOR CURRENT, 200mA/div (I
= 100mA)
OUT
OUT
_______________________________________________________________________________________
7
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
(V = 12V, V
IN
= 12V, T = -40°C to +125°C, unless otherwise noted. Typical values are at T = +25°C. See the Typical
ON/OFF
A
A
Application Circuit, if applicable.)
MAX5035DASA STARTUP WAVEFORM
MAX5035DASA LX WAVEFORMS
(I = 0)
O
MAX5035 toc23
MAX5035 toc22
A
B
MAX035
A
0
0
0
B
0
1ms/div
4μs/div
A: V
ON/OFF
, 2V/div
A: SWITCH VOLTAGE (LX PIN), 20V/div (V = 48V)
IN
B: V , 2V/div
OUT
B: INDUCTOR CURRENT, 200mA/div (I
= 0)
OUT
MAX5035DASA STARTUP WAVEFORM
PEAK SWITCH CURRENT LIMIT
vs. INPUT VOLTAGE
(I = 1A)
O
MAX5035 toc24
3.0
2.5
2.0
1.5
1.0
0.5
A
B
0
0
MAX5035DASA
V
OUT
= 5V
5% DROP IN V
OUT
1ms/div
6
16
26
36
46
56
66
76
INPUT VOLTAGE (V)
A: V
ON/OFF
, 2V/div
B: V , 2V/div
OUT
8
_______________________________________________________________________________________
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
MAX035
Pin Description
PIN
1
NAME
BST
FUNCTION
Boost Capacitor Connection. Connect a 0.1µF ceramic capacitor from BST to LX.
Internal Regulator Output. Bypass VD to GND with a 0.1µF ceramic capacitor.
Internal Connection. SGND must be connected to GND.
2
VD
3
SGND
Output Sense Feedback Connection. For fixed output voltage (MAX5035A, MAX5035B, MAX5035C),
connect FB to V . For adjustable output voltage (MAX5035D), use an external resistive voltage-divider to
OUT
4
FB
set V
. V regulating set point is 1.22V.
OUT FB
Shutdown Control Input. Pull ON/OFF low to put the device in shutdown mode. Drive ON/OFF high for
normal operation.
5
ON/OFF
6
7
8
GND
Ground
V
Input Voltage. Bypass V to GND with a low ESR capacitor as close to the device as possible.
IN
IN
LX
Source Connection of Internal High-Side Switch
Block Diagram
V
IN
ON/OFF
ENABLE
REGULATOR
(FOR ANALOG)
I
CPFM
CILIM
REF-PFM
1.69V
HIGH-SIDE
CURRENT
SENSE
REGULATOR
(FOR DRIVER)
VD
OSC
V
RAMP
REF
I
REF-LIM
BST
MAX5035
CLK
CONTROL
LOGIC
FB
RAMP
R
h
TYPE 3
COMPENSATION
x1
THERMAL
SHUTDOWN
CPWM
V
R
REF
l
EAMP
GND
LX
SGND
_______________________________________________________________________________________
9
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
0.1µF, 16V ceramic capacitor located as close to the
device as possible.
Detailed Description
The MAX5035 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 effi-
ciency over a wide input voltage range. This pulse-
width modulated converter operates at a fixed 125kHz
switching frequency. The device also features automat-
ic pulse-skipping mode to provide low quiescent cur-
rent and high efficiency at light loads. Under no load,
the MAX5035 consumes only 270µA, and in shutdown
mode, consumes only 10µA. The MAX5035 also fea-
tures undervoltage lockout, hiccup mode output short-
circuit protection, and thermal shutdown.
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.
MAX035
Thermal-Overload Protection
The MAX5035 features integrated thermal overload pro-
tection. Thermal overload protection limits total power
dissipation 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 allowing the IC to cool. The thermal sensor turns the
internal power MOSFET back on after the IC’s die tem-
perature cools down to +140°C, resulting in a pulsed
output under continuous thermal overload conditions.
Shutdown Mode
Drive ON/OFF to ground to shut down the MAX5035.
Shutdown forces the internal power MOSFET off, turns
off all internal circuitry, and reduces the V supply cur-
IN
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.
Applications Information
Setting the Output Voltage
The MAX5035A/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).
Undervoltage Lockout (UVLO)
Use the ON/OFF function to program the UVLO thresh-
old at the input. Connect a resistive voltage-divider
The MAX5035D offers an adjustable output voltage. Set
the output voltage with a resistive voltage-divider con-
nected 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:
from V to GND with the center node to ON/OFF as
IN
shown in Figure 1. Calculate the threshold value by
using the following formula:
R1
R2
⎛
⎝
⎞
VUVLO(TH) = 1 +
× 1.85V
⎜
⎟
⎠
(V
−1.22)
1.22
OUT
R3 =
× R4
The minimum recommended V
is 6.5V, 7.5V,
UVLO(TH)
and 13V for the output voltages of 3.3V, 5V, and 12V,
respectively. The recommended value for R2 is less
than 1MΩ.
V
IN
7.5V TO 76V
If the external UVLO threshold-setting divider is not
used, an internal undervoltage-lockout feature monitors
68μF
V
5V
OUT
100μH
V
the supply voltage at V and allows operation to start
IN
IN
LX
R1
R2
when V rises above 5.2V (typ). This feature can be
IN
0.1μF
C
68μF
OUT
D1
50SQ100
used only when V rise time is faster than 2ms. For
IN
ON/OFF
BST
slower V rise time, use the resistive-divider at
IN
R3
ON/OFF.
MAX5035D
41.2kΩ
FB
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
VD
R4
SGND GND
13.3kΩ
0.1μF
Figure 1. Adjustable Output Voltage
10 ______________________________________________________________________________________
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
MAX035
The MAX5035 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.
drop (V ) less than 0.45V at +25°C and maximum load
FB
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.
Inductor Selection
The choice of an inductor is guided by the voltage dif-
ference between V and V
, the required output
OUT
Input Bypass Capacitor
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 MAX5035 high switching frequency
allows the use of smaller-value input capacitors.
IN
current, and the operating frequency of the circuit. Use
an inductor with a minimum value given by:
(V − V
) × D
IN
OUT
L =
0.3 × I
× f
SW
OUTMAX
where:
The input ripple is comprised of ΔV (caused by the
Q
V
V
OUT
capacitor discharge) and ΔV
(caused by the ESR of
ESR
D =
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, cal-
culate the input capacitance and the ESR required for a
specified ripple using the following equations:
IN
I
is the maximum output current required, and
OUTMAX
f
is the operating frequency of 125kHz. Use an induc-
SW
tor with a maximum saturation current rating equal to at
least the peak switch current limit (I ). Use inductors
LIM
with low DC resistance for higher efficiency.
ΔVESR
ESR
=
IN
Selecting a Rectifier
The MAX5035 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
ΔIL
⎛
⎞
I
+
⎜
⎟
OUT
2
⎝
⎠
IOUT × D (1−D)
ΔVQ × fSW
CIN
=
where
expected input voltage, V . Use a low forward-voltage
IN
(V − VOUT) × VOUT
Schottky rectifier for proper operation and high efficien-
cy. Avoid higher than necessary reverse-voltage
Schottky rectifiers that have higher forward-voltage
drops. Use a Schottky rectifier with forward-voltage
IN
ΔIL =
,
V
× fSW × L
IN
V
V
OUT
D =
Table 1. Diode Selection
IN
I
is the maximum output current of the converter
OUT
and f
V
(V) DIODE PART NUMBER
MANUFACTURER
IR
IN
is the oscillator switching frequency (125kHz).
SW
15MQ040N
For example, at V = 48V, V
= 3.3V, the ESR and
OUT
IN
B240A
Diodes, Inc.
input capacitance are calculated for the input peak-to-
peak ripple of 100mV or less yielding an ESR and
capacitance value of 80mΩ and 51µF, respectively.
7.5 to 36
B240
MBRS240, MBRS1540
30BQ060
Central Semiconductor
ON Semiconductor
IR
Low-ESR, ceramic, multilayer chip capacitors are recom-
mended for size-optimized application. For ceramic
capacitors, assume the contribution from ESR and capaci-
tor discharge is equal to 10% and 90%, respectively.
B360A
Diodes, Inc.
7.5 to 56
7.5 to 76
CMSH3-60
Central Semiconductor
ON Semiconductor
IR
MBRD360, MBR3060
50SQ100, 50SQ80
MBRM5100
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.
Diodes, Inc.
______________________________________________________________________________________ 11
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
Ensure that the ripple specification of the input capaci-
tor exceeds the worst-case capacitor RMS ripple cur-
rent. Use the following equations to calculate the input
capacitor RMS current:
capacitance and the ESR required for a specified rip-
ple using the following equations:
ΔV
OESR
ESR
=
OUT
ΔI
L
2
2
I
=
I
− I
AVGIN
CRMS
PRMS
where
ΔI
L
C
≈
OUT
2.2 × ΔV
× f
OQ SW
D
3
MAX035
2
2
⎛
⎞
I
=
I
+ I
+ I
× I
DC
×
(
)
⎠
PRMS
PK
DC
PK
⎝
The MAX5035 has an internal soft-start time (t ) of
SS
V
×I
× η
OUT OUT
400µs. It is important to keep the output rise time at
I
=
AVGIN
V
startup below t to avoid output overshoot. The output
SS
IN
rise time is directly proportional to the output capacitor.
Use 68µF or lower capacitance at the output to control
the overshoot below 5%.
ΔI
2
ΔI
L
2
L
I
=I
+
, I = I
−
PK OUT
DC
OUT
V
OUT
and D =
In a dynamic load application, the allowable deviation
of the output voltage during the fast-transient load dic-
tates 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
V
IN
I
is the input switch RMS current, I
input average current, and η is the converter efficiency.
is the
AVGIN
PRMS
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.
response time (t
) depends on the closed-
RESPONSE
loop bandwidth of the converter. The resistive drop
across the capacitor ESR and capacitor discharge
cause a voltage droop during a step load. Use a com-
bination 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 electronics being powered.
Assuming a 50% contribution each from the output
capacitance discharge and the ESR drop, use the fol-
lowing equations to calculate the required ESR and
capacitance value:
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 dur-
ing load steps determine the capacitance and the ESR
requirements 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
ΔV
OESR
ESR
=
OUT
I
STEP
(f ) occurs between 20kHz to 40kHz. Use the following
Z
equation to verify the value of f . Capacitors with 100mΩ
Z
to 250mΩ ESR are recommended to ensure the closed-
I
× t
ΔV
STEP
RESPONSE
C
=
OUT
loop stability, while keeping the output ripple low.
OQ
1
fZ =
where I
is the load step and t
is the
RESPONSE
STEP
2 × π × COUT × ESROUT
response time of the controller. Controller response
time is approximately one-third of the reciprocal of the
closed-loop unity-gain bandwidth, 20kHz typically.
The output ripple is comprised of ΔV
(caused by the
OQ
capacitor discharge) and ΔV
(caused by the ESR
OESR
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
PC Board Layout Considerations
Proper PC board 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”
12 ______________________________________________________________________________________
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
MAX035
ground configuration). A ground plane is required.
device. Also, place BST and VD bypass capacitors
very close to the device. Use the PC board copper
Minimize lead lengths to reduce stray capacitance,
trace resistance, and radiated noise. In particular,
place the Schottky rectifier diode right next to the
plane connecting to V and LX for heatsinking.
IN
Application Circuits
V
IN
C
IN
V
IN
BST
LX
0.1μF
L1
V
OUT
D1
R1
R2
C
OUT
MAX5035
ON/OFF
FB
VD
SGND GND
0.1μF
Figure 2. Fixed Output Voltages
Table 2. Typical External Components Selection (Circuit of Figure 2)
V
(V)
V
(V)
I (A)
OUT
EXTERNAL COMPONENTS
IN
OUT
C
C
C
= 68µF, Panasonic, EEVFK2A680Q
IN
= 68µF, Vishay Sprague, 594D686X_010C2T
= 0.1µF, 0805
OUT
BST
7.5 to 76
7.5 to 76
7.5 to 76
7.5 to 76
3.3
0.5
R1 = 1MΩ 1%, 0805
R2 = 384kΩ 1%, 0805
D1 = 50SQ100, IR
L1 = 100µH, Coilcraft Inc., DO5022P-104
3.3
5
1
C
C
C
= 68µF, Panasonic, EEVFK2A680Q
IN
= 68µF, Vishay Sprague, 594D68X_010C2T
= 0.1µF, 0805
OUT
0.5
1
BST
R1 = 1MΩ 1%, 0805
R2 = 384kΩ 1%, 0805
D1 = 50SQ100, IR
5
L1 = 100µH, Coilcraft Inc., DO5022P-104
C
C
C
= 68µF, Panasonic, EEVFK2A680Q
IN
= 15µF, Vishay Sprague, 594D156X0025C2T
= 0.1µF, 0805
OUT
BST
R1 = 1MΩ 1%, 0805
15 to 76
12
1
R2 = 139kΩ 1%, 0805
D1 = 50SQ100, IR
L1 = 220µH, Coilcraft Inc., DO5022P-224
______________________________________________________________________________________ 13
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
Table 2. Typical External Components Selection (Circuit of Figure 2) (continued)
V
(V)
V
(V)
I
(A)
EXTERNAL COMPONENTS
IN
OUT
OUT
C
C
C
= 220µF, Panasonic, EEVFK1E221P
IN
= 68µF, Vishay Sprague, 594D686X_010C2T
= 0.1µF, 0805
OUT
BST
3.3
1
R1 = 1MΩ 1%, 0805
R2 = 274kΩ 1%, 0805
D1 = B220, Diodes Inc.
MAX035
L1 = 100µH, Coilcraft Inc., DO5022P-104
9 to 14
C
C
C
= 220µF, Panasonic, EEVFK1E221P
IN
= 68µF, Vishay Sprague, 594D686X_010C2T
= 0.1µF, 0805
OUT
BST
5
3.3
5
1
1
1
1
R1 = 1MΩ 1%, 0805
R2 = 274kΩ 1%, 0805
D1 = B220, Diodes Inc.
L1 = 100µH, Coilcraft Inc., DO5022P-104
C
C
C
= 220µF, Panasonic, EEVFK1H221P
IN
= 68µF, Vishay Sprague, 594D686X_010C2T
= 0.1µF, 0805
OUT
BST
R1 = 1MΩ 1%, 0805
R2 = 130kΩ 1%, 0805
D1 = MBRS2040, ON Semiconductor
L1 = 100µH, Coilcraft Inc., DO5022P-104
C
C
C
= 220µF, Panasonic, EEVFK1H221P
IN
= 68µF, Vishay Sprague, 594D686X_010C2T
= 0.1µF, 0805
OUT
BST
18 to 36
R1 = 1MΩ 1%, 0805
R2 = 130kΩ 1%, 0805
D1 = MBRS2040, ON Semiconductor
L1 = 100µH, Coilcraft Inc., DO5022P-104
C
C
C
= 220µF, Panasonic, EEVFK1H221P
IN
= 15µF, Vishay Sprague, 594D156X_0025C2T
= 0.1µF, 0805
OUT
BST
12
R1 = 1MΩ 1%, 0805
R2 = 130kΩ 1%, 0805
D1 = MBRS2040, ON Semiconductor
L1 = 220µH, Coilcraft Inc., DO5022P-224
14 ______________________________________________________________________________________
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
MAX035
Table 3. Component Suppliers
SUPPLIER
PHONE
FAX
WEBSITE
www.avxcorp.com
www.coilcraft.com
www.diodes.com
AVX
843-946-0238
847-639-6400
805-446-4800
714-373-7366
619-661-6835
847-803-6100
402-563-6866
843-626-3123
847-639-1469
805-446-4850
714-737-7323
619-661-1055
847-390-4405
402-563-6296
Coilcraft
Diodes Incorporated
Panasonic
Sanyo
www.panasonic.com
www.sanyo.com
TDK
www.component.tdk.com
www.vishay.com
Vishay
MAX5035
FB
BST
PTC*
ON/OFF
L1
100μH
V
OUT
0.1μF
5V AT 1A
V
12V
IN
V
IN
LX
C
68μF
IN
VD
Rt
Ct
D1
B240
SGND GND
C
OUT
68μF
0.1μF
*LOCATE PTC AS CLOSE TO HEAT-DISSIPATING COMPONENTS AS POSSIBLE.
Figure 3. Load Temperature Monitoring with ON/OFF (Requires Accurate V
)
IN
______________________________________________________________________________________ 15
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
FB
MAX5035B
R1
BST
ON/OFF
L1
220μH
V
5V
OUT
0.1μF
V
IN
V
LX
IN
7.5V TO 36V
C
68μF
OUT
MAX035
C
68μF
IN
VD
Rt
Ct
D1
B240
SGND GND
0.1μF
FB
MAX5035A
R1'
BST
ON/OFF
L1'
100μH
V'
3.3V
OUT
0.1μF
V
IN
LX
C'
68μF
OUT
C'
68μF
IN
VD
Rt'
Ct'
D1'
B240
SGND GND
0.1μF
Figure 4. Dual-Sequenced DC-DC Converters (Startup Delay Determined by R1/R1’, Ct/Ct’ and Rt/Rt’)
Ordering Information (continued)
Chip Information
TRANSISTOR COUNT: 4344
OUTPUT
VOLTAGE
(V)
PIN-
PACKAGE
PART
TEMP RANGE
PROCESS: BiCMOS
MAX5035CUSA
MAX5035CUPA
MAX5035CASA
0°C to +85°C
0°C to +85°C
8 SO
8 PDIP
12
Package Information
-40°C to +125°C 8 SO
For the latest package outline information and land patterns, go
MAX5035CASA/V+ -40°C to +125°C 8 SO
to www.maxim-ic.com/packages.
MAX5035DUSA
MAX5035DUPA
MAX5035DASA
0°C to +85°C
0°C to +85°C
8 SO
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
8 PDIP
ADJ
8 SO
S8+2
P8+1
21-0041
21-0043
-40°C to +125°C 8 SO
8 PDIP
MAX5035DASA/V+ -40°C to +125°C 8 SO
+Denotes lead(Pb)-free/RoHS-compliant package.
16 ______________________________________________________________________________________
1A, 76V, High-Efficiency MAXPower
Step-Down DC-DC Converter
MAX035
Revision History
REVISION
NUMBER
REVISION
DATE
PAGES
CHANGED
DESCRIPTION
0
9/03
Initial release
—
Modified Absolute Maximum Ratings section, updated Ordering Information,
style edits.
3
5/09
1, 2, 16, 18
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17
© 2009 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.
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