_______________General Description
The MAX727/MAX728/MAX729 are monolithic, bipolar,
pulse-width modulation (PWM), switch-mode, step-down
DC-DC regulators. Each is rated at 2A. Very few external
components are needed for standard operation because
the power switch, oscillator, feedback, and control circuitry
are all on-chip. Employing a classic buck topology, these
regulators perform high-current step-down functions.
These regulators have excellent dynamic and transient
response characteristics, while featuring cycle-by-cycle cur-
rent limiting to protect against overcurrent faults and short-
circuit output faults. They also have a wide 8V to 40V input
range.
Each regulator is available in a 5-pin TO-220 package.
These devices have a preset 100kHz oscillator frequency
and a preset current limit of 2.6A. See the MAX724/
MAX726 data sheet for more applications information.
_______________________Applications
Distributed Power from High-Voltage Buses
High-Current, High-Voltage Step-Down Applications
Multiple-Output Buck Converter
MAX727/MAX728/MAX729
5V/3.3V/3V 2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
________________________________________________________________
Maxim Integrated Products
1
V
IN
V
SW
GND
V
C
SENSE
CASE IS CONNECTED TO GROUND. STANDARD PACKAGE HAS STAGGERED LEADS.
CONTACT FACTORY FOR STRAIGHT LEADS.
5-PIN TO-220
FRONT VIEW
MAX727
MAX728
MAX729
1
2
3
4
5
__________________Pin Configuration
VIN
VC
VSW
220
µ
F
GND
2.7k
0.01
µ
F
OUTPUT
5V AT 2A
SENSE
100
µ
H
MBR745
470
µ
F
INPUT
8V TO 40V
MAX727
STEP-DOWN CONVERTER
__________Typical Operating Circuit
Call toll free 1-800-998-8800 for free samples or literature.
19-0149; Rev 2; 9/95
___________________________Features
o
Input Range: Up to 40V
o
2A On-Chip Power Switch
o
Fixed Outputs: 5V (MAX727)
3.3V (MAX728)
3V (MAX729)
o
100kHz Switching Frequency
o
Excellent Dynamic Characteristics
o
Few External Components
o
8.5mA Quiescent Current
o
TO-220 Package
______________Ordering Information
PART
MAX727
CCK
MAX727ECK
-40°C to +85°C
0°C to +70°C
TEMP. RANGE
PIN-PACKAGE
5 TO-220
5 TO-220
MAX728
CCK
MAX728ECK
-40°C to +85°C
0°C to +70°C
5 TO-220
5 TO-220
MAX729
CCK
MAX729ECK
-40°C to +85°C
0°C to +70°C
5 TO-220
5 TO-220
MAX727/MAX728/MAX729
5V/3.3V/3V 2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
2
_______________________________________________________________________________________
Input Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45V
Switch Voltage with Respect to Input Voltage. . . . . . . . . . . . . . . . 50V
Switch Voltage with Respect to GND Pin (V
SW
negative)
(Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35V
SENSE Pin Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V, +10V
Operating Temperature Ranges
MAX72_CCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0°C to +70°C
MAX72_ECK. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -40°C to +85°C
Junction Temperature Ranges:
MAX72_CCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0°C to +125°C
MAX72_ECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 40°C to +125°C
Storage Temperature Range . . . . . . . . . . . . . . . . . . . -65°C to +160°C
Lead Temperature (soldering, 10sec). . . . . . . . . . . . . . . . . . . . +300°C
ELECTRICAL CHARACTERISTICS
(V
IN
= 25V, T
j
= T
MIN
to T
MAX
, unless otherwise noted.)
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.
ABSOLUTE MAXIMUM RATINGS
mA
3.5
4.8
Start-Up Mode (Note 4)
V
7.3
8.0
Normal Mode
Minimum Supply Voltage
8.5
11
V
IN
40V, V
SENSE
= 5.5V
T
j
= +25°C
µA
250
T
j
= +25°C
T
j
= +25°C
V
IN
= 40V, V
SW
= 0V
Switch-Off Leakage
T
j
= +25°C
T
j
= +25°C
mA
T
j
+125°C
150
0.6
1.0
1.7
V
SENSE
= V
OUT
+ 10%
V
IN
= 25V, V
SW
= 0V
Error-Amplifier Sink Current
µA
T
j
= +25°C
100
140
225
V
SENSE
= V
OUT
- 10%
Error-Amplifier Source Current
µmho
1.7
3000
5000
9000
I
SW
= 2A
Error-Amplifier Transconductance
V/V
V
1.2
2000
1V
V
C
4V
I
SW
= 0.5A
Error-Amplifier Voltage Gain
Switch-On Voltage (Note 2)
%/V
0.03
0.10
kHz
Switching Frequency
20
V
OUT
= V
SENSE
= 0V (Note 5)
85
120
T
j
= +25°C
90
100
110
T
j
= +25°C
%
85
90
Maximum Duty Cycle
8V
V
IN
40V
Switching Frequency Line Regulation
UNITS
MIN
TYP
MAX
3.5
5.0
CONDITIONS
PARAMETER
Supply Current (Note 3)
2.0
2.6
3.2
A
Switch-Current Limit (Note 5)
V
8.0
40.0
Input Supply Voltage Range
T
j
0°C
T
j
< 0°C
MAX727/MAX728/MAX729
5V/3.3V/3V 2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
_______________________________________________________________________________________
3
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 25V, T
j
= T
MIN
to T
MAX
, unless otherwise noted.)
Note 1:
Do not exceed switch-to-input voltage limitation.
Note 2:
For switch currents between 1A and 2A, maximum switch-on voltage can be calculated via linear interpolation.
Note 3:
By setting the SENSE pin to 5.5V, the V
C
pin is forced to its low clamp level and the switch duty cycle is forced to zero,
approximating the zero load condition.
Note 4:
For proper regulation, total voltage from V
IN
to GND must be
8V after start-up.
Note 5:
To avoid extremely short switch-on times, the switch frequency is internally scaled down when V
SENSE
is less than 2.6V
(MAX727), 2.0V (MAX728), or 1.8V (MAX729). Switch current limit is tested with V
SENSE
adjusted to give a 1µs minimum
switch-on time.
Note 6:
Guaranteed, not production tested.
0% duty cycle
0% duty cycle
V
C
Voltage Temperature Coefficient
mV/°C
Thermal Resistance Junction to Case
(Note 6)
°C/W
4.0
V
-4
T
j
= T
MIN
to T
MAX
V
C
Voltage
1.5
T
j
= +25°C
Output Voltage Line Regulation
%/V
0.005
0.020
8V
V
IN
40V
±1.0
±3.0
T
j
= T
MIN
to
T
MAX
V
OUT
(nominal) = 5V (MAX727),
3.3V (MAX728), or 3V (MAX729);
all conditions of input voltage,
output voltage, and load
current
Output Voltage Tolerance
%
±0.5
±2.0
T
j
= +25°C
MAX729
MAX728
MAX727
MAX729
MAX728
MAX727
CONDITIONS
2.2
3.8
6.5
T
j
= +25°C
SENSE Pin Divider Resistance
2.5
4.2
7.0
k
3.0
5.0
8.0
2.90
3.00
3.10
V
C
= 2V
SENSE Voltage
3.20
3.30
3.40
V
4.85
5.00
5.15
UNITS
MIN
TYP
MAX
PARAMETER
______________________________________________________________Pin Description
5
V
IN
supplies power to the internal circuitry and also connects to the collector of the internal power
switch. V
IN
must be bypassed with a low-ESR capacitor, typically 200µF or 220µF.
Internal Power Switch Output. The
S
witch output can swing 35V below ground and is rated for 2A.
Ground requires a short, low-noise connection to ensure good load regulation. The internal refer-
ence is referred to GND, so errors at this pin are multiplied by the error amplifier.
Error-Amplifier Output. A series RC network connected to this pin compensates the
MAX727/MAX728/MAX729. Output swing is limited to about 5.8V in the positive direction and
-0.7V in the negative direction. V
C
can also synchronize the MAX727/MAX728/MAX729 to an
external TTL clock in the 115kHz to 170kHz range. See MAX724/MAX726 data sheet.
SENSE Input is the internal error amplifier's input, and should be directly connected to V
OUT
.
SENSE also aids current limiting by reducing oscillator frequency when V
OUT
is low.
4
3
2
1
PIN
V
IN
V
SW
GND
V
C
SENSE
FUNCTION
NAME
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.
4
___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1995 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
MAX727/MAX728/MAX729
5V/3.3V/3V 2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
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.
4
___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600
© 1995 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
E
F
B
DIM
A
B
C1
D
E
e
F
H1
J1
L
P
Q
MIN
0.140
0.015
0.014
0.560
0.380
0.045
0.230
0.080
0.500
0.139
0.100
MAX
0.190
0.040
0.022
0.650
0.420
0.055
0.270
0.115
0.580
0.161
0.120
MIN
3.56
0.38
0.41
14.23
9.66
1.14
5.85
2.04
12.70
3.54
2.54
MAX
4.82
1.01
0.50
16.51
10.66
1.39
6.85
2.92
14.73
4.08
3.04
INCHES
MILLIMETERS
e
21-4737-
5-PIN TO-220
(STRAIGHT LEAD)
PACKAGE
1.70 BSC
0.067 BSC
P
H1
Q
D
A
J1
C1
L
________________________________________________________Package Information
E
J3
F
B
DIM
A
B
C1
D
E
e
F
H1
J1
J2
J3
L
L1
L2
P
Q
MIN
0.140
0.015
0.014
0.560
0.380
0.045
0.230
0.080
0.170
0.327
0.170
0.260
0.700
0.139
0.100
MAX
0.190
0.040
0.022
0.650
0.420
0.055
0.270
0.115
0.185
0.335
0.200
0.340
0.720
0.161
0.120
MIN
3.56
0.38
0.41
14.23
9.66
1.14
5.85
2.04
4.32
8.31
4.32
6.60
17.78
3.54
2.54
MAX
4.82
1.01
0.50
16.51
10.66
1.39
6.85
2.92
4.70
8.51
5.08
8.64
18.29
4.08
3.04
INCHES
MILLIMETERS
e
21-005-
5-PIN TO-220
(STAGGERED LEAD)
PACKAGE
1.70 BSC
0.067 BSC
P
H1
Q
D
A
L2
J1
L1
L
C1
J2
CONTACT FACTORY FOR AVAILABILITY
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