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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 current limiting to protect against overcurrent faults and shortcircuit 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 0C to +70C -40C to +85C 0C to +70C -40C to +85C 0C to +70C -40C to +85C 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 220F VSW
100H
OUTPUT 5V AT 2A
MAX727
VC 2.7k GND 0.01F SENSE
MBR745 470F
MAX727 MAX728 MAX729
5 4 3 2 1
VIN VSW GND VC 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
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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 (VSW negative) (Note 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35V SENSE Pin Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V, +10V Operating Temperature Ranges MAX72_CCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0C to +70C MAX72_ECK. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -40C to +85C Junction Temperature Ranges: MAX72_CCK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0C to +125C MAX72_ECK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . - 40C to +125C Storage Temperature Range . . . . . . . . . . . . . . . . . . . -65C to +160C Lead Temperature (soldering, 10sec). . . . . . . . . . . . . . . . . . . . +300C
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
(VIN = 25V, Tj = TMIN to TMAX, unless otherwise noted.) PARAMETER Input Supply Voltage Range Switch-On Voltage (Note 2) Switch-Off Leakage Supply Current (Note 3) ISW = 0.5A ISW = 2A VIN = 25V, VSW = 0V VIN = 40V, VSW = 0V VIN 40V, VSENSE = 5.5V Normal Mode Minimum Supply Voltage Start-Up Mode (Note 4) Switch-Current Limit (Note 5) Maximum Duty Cycle Tj = +25C Switching Frequency Switching Frequency Line Regulation Error-Amplifier Voltage Gain Error-Amplifier Transconductance Error-Amplifier Source Current Error-Amplifier Sink Current VSENSE = VOUT - 10% VSENSE = VOUT + 10% 8V VIN 40V 1V VC 4V Tj = +25C Tj = +25C Tj = +25C Tj = +25C 3000 100 0.6 Tj +125C VOUT = VSENSE = 0V (Note 5) Tj = +25C Tj 0C Tj < 0C 2.0 85 90 85 20 0.03 2000 5000 140 1.0 9000 225 1.7 0.10 %/V V/V mho A mA Tj = +25C Tj = +25C 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 A mA
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5V/3.3V/3V 2A Step-Down, PWM, Switch-Mode DC-DC Regulators
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 25V, Tj = TMIN to TMAX, unless otherwise noted.) PARAMETER SENSE Voltage VC = 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 Tj = +25C Tj = TMIN to TMAX 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
Tj = +25C
k
Output Voltage Tolerance
VOUT (nominal) = 5V (MAX727), 3.3V (MAX728), or 3V (MAX729); Tj = +25C all conditions of input voltage, Tj = TMIN to output voltage, and load TMAX current 8V VIN 40V 0% duty cycle 0% duty cycle
Output Voltage Line Regulation VC Voltage VC 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 VC 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 VIN 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 VSENSE is less than 2.6V (MAX727), 2.0V (MAX728), or 1.8V (MAX729). Switch current limit is tested with VSENSE adjusted to give a 1s 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 VOUT. SENSE also aids current limiting by reducing oscillator frequency when VOUT 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. VC 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 reference is referred to GND, so errors at this pin are multiplied by the error amplifier. Internal Power Switch Output. The Switch output can swing 35V below ground and is rated for 2A. VIN supplies power to the internal circuitry and also connects to the collector of the internal power switch. VIN must be bypassed with a low-ESR capacitor, typically 200F or 220F.
2
VC
3 4 5
GND VSW VIN
_______________________________________________________________________________________
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5V/3.3V/3V 2A Step-Down, PWM, Switch-Mode DC-DC Regulators MAX727/MAX728/MAX729
________________________________________________________Package Information
A E Q H1 P F
DIM A B C1 D E e F H1 J1 J2 J3 L L1 L2 P 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 P F
DIM A B C1 D E e F H1 J1 L P 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 (c) 1995 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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