Not Recommended for New Designs
This product was manufactured for Maxim by an outside wafer foundry
using a process that is no longer available. It is not recommended for
new designs. The data sheet remains available for existing users.
A Maxim replacement or an industry second-source may be available.
Please see the QuickView data sheet for this part or contact technical
support for assistance.
For further information,
contact Maxim’s Applications Tech Support.
19-0149; Rev 2; 9/95
5V/3.3V/3V 2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
_______________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.
___________________________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
MAX727/MAX728/MAX729
______________Ordering Information
PART
MAX727CCK
MAX727ECK
MAX728CCK
MAX728ECK
MAX729CCK
MAX729ECK
TEMP. RANGE
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
0°C to +70°C
-40°C to +85°C
PIN-PACKAGE
5 TO-220
5 TO-220
5 TO-220
5 TO-220
5 TO-220
5 TO-220
_______________________Applications
Distributed Power from High-Voltage Buses
High-Current, High-Voltage Step-Down Applications
Multiple-Output Buck Converter
__________Typical Operating Circuit
__________________Pin Configuration
FRONT VIEW
INPUT
8V TO 40V
VIN
220µF
VSW
100µH
OUTPUT
5V AT 2A
MAX727
VC
2.7k
GND
0.01µF
SENSE
MBR745
470µF
MAX727
MAX728
MAX729
5
4
3
2
1
V
IN
V
SW
GND
V
C
SENSE
5-PIN TO-220
CASE IS CONNECTED TO GROUND. STANDARD PACKAGE HAS STAGGERED LEADS.
CONTACT FACTORY FOR STRAIGHT LEADS.
STEP-DOWN CONVERTER
________________________________________________________________
Maxim Integrated Products
1
Call toll free 1-800-998-8800 for free samples or literature.
5V/3.3V/3V 2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
MAX727/MAX728/MAX729
ABSOLUTE MAXIMUM RATINGS
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
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
(V
IN
= 25V, T
j
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
Input Supply Voltage Range
Switch-On Voltage (Note 2)
Switch-Off Leakage
Supply Current (Note 3)
I
SW
= 0.5A
I
SW
= 2A
V
IN
= 25V, V
SW
= 0V
V
IN
= 40V, V
SW
= 0V
V
IN
≤
40V, V
SENSE
= 5.5V
Normal Mode
Minimum Supply Voltage
Start-Up Mode (Note 4)
Switch-Current Limit (Note 5)
Maximum Duty Cycle
T
j
= +25°C
Switching Frequency
Switching Frequency Line Regulation
Error-Amplifier Voltage Gain
Error-Amplifier Transconductance
Error-Amplifier Source Current
Error-Amplifier Sink Current
V
SENSE
= V
OUT
- 10%
V
SENSE
= V
OUT
+ 10%
8V
≤
V
IN
≤
40V
1V
≤
V
C
≤
4V
T
j
= +25°C
T
j
= +25°C
T
j
= +25°C
T
j
= +25°C
3000
100
0.6
T
j
≤
+125°C
V
OUT
= V
SENSE
= 0V (Note 5) T
j
= +25°C
T
j
≥
0°C
T
j
< 0°C
2.0
85
90
85
20
0.03
2000
5000
140
1.0
9000
225
1.7
0.10
%/V
V/V
µmho
µA
mA
T
j
= +25°C
T
j
= +25°C
8.5
7.3
3.5
3.5
2.6
90
100
110
120
kHz
CONDITIONS
MIN
8.0
TYP
MAX
40.0
1.2
1.7
150
250
11
8.0
4.8
5.0
3.2
A
%
V
UNITS
V
V
µA
mA
2
_______________________________________________________________________________________
5V/3.3V/3V 2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
ELECTRICAL CHARACTERISTICS (continued)
(V
IN
= 25V, T
j
= T
MIN
to T
MAX
, unless otherwise noted.)
PARAMETER
SENSE Voltage
V
C
= 2V
CONDITIONS
MAX727
MAX728
MAX729
MAX727
MAX728
MAX729
MIN
4.85
3.20
2.90
3.0
2.5
2.2
TYP
5.00
3.30
3.00
5.0
4.2
3.8
±0.5
±1.0
0.005
T
j
= +25°C
T
j
= T
MIN
to T
MAX
1.5
-4
4.0
MAX
5.15
3.40
3.10
8.0
7.0
6.5
±2.0
%
±3.0
0.020
%/V
V
mV/°C
°C/W
UNITS
V
MAX727/MAX728/MAX729
SENSE Pin Divider Resistance
T
j
= +25°C
kΩ
Output Voltage Tolerance
V
OUT
(nominal) = 5V (MAX727),
3.3V (MAX728), or 3V (MAX729); T
j
= +25°C
all conditions of input voltage,
T
j
= T
MIN
to
output voltage, and load
T
MAX
current
8V
≤
V
IN
≤
40V
0% duty cycle
0% duty cycle
Output Voltage Line Regulation
V
C
Voltage
V
C
Voltage Temperature Coefficient
Thermal Resistance Junction to Case
(Note 6)
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.
______________________________________________________________Pin Description
PIN
1
NAME
SENSE
FUNCTION
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.
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.
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.
Internal Power Switch Output. The
S
witch output can swing 35V below ground and is rated for 2A.
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.
2
V
C
3
4
5
GND
V
SW
V
IN
_______________________________________________________________________________________
3
5V/3.3V/3V 2A Step-Down, PWM,
Switch-Mode DC-DC Regulators
MAX727/MAX728/MAX729
________________________________________________________Package Information
A
E
Q
H1
φP
F
DIM
A
B
C1
D
E
e
F
H1
J1
J2
J3
L
L1
L2
φP
Q
INCHES
MAX
MIN
0.190
0.140
0.040
0.015
0.022
0.014
0.650
0.560
0.420
0.380
0.067 BSC
0.055
0.045
0.270
0.230
0.115
0.080
0.185
0.170
0.335
0.327
0.200
0.170
0.340
0.260
0.720
0.700
0.161
0.139
0.120
0.100
MILLIMETERS
MIN
MAX
3.56
4.82
0.38
1.01
0.41
0.50
14.23
16.51
9.66
10.66
1.70 BSC
1.14
1.39
5.85
6.85
2.04
2.92
4.32
4.70
8.31
8.51
4.32
5.08
6.60
8.64
17.78
18.29
3.54
4.08
2.54
3.04
21-005-
D
L2
J1
L
L1
C1
B
e
J2
J3
INCHES
MAX
MIN
0.190
0.140
0.040
0.015
0.022
0.014
0.650
0.560
0.420
0.380
0.067 BSC
0.055
0.045
0.270
0.230
0.115
0.080
0.580
0.500
0.161
0.139
0.120
0.100
5-PIN TO-220
(STAGGERED LEAD)
PACKAGE
MILLIMETERS
MIN
MAX
3.56
4.82
0.38
1.01
0.41
0.50
14.23
16.51
9.66
10.66
1.70 BSC
1.14
1.39
5.85
6.85
2.04
2.92
12.70
14.73
3.54
4.08
2.54
3.04
21-4737-
A
E
Q
H1
φP
F
DIM
A
B
C1
D
E
e
F
H1
J1
L
φP
Q
D
J1
L
B
e
C1
5-PIN TO-220
(STRAIGHT LEAD)
PACKAGE
CONTACT FACTORY FOR AVAILABILITY
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.
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