19-0149; Rev 2; 9/955V/3.3V/3V 2A Step-Down, PWM,Switch-Mode DC-DCRegulators_______________General DescriptionThe MAX727/MAX728/MAX729 are monolithic, bipolar,pulse-width modulation (PWM), switch-mode, step-downDC-DC regulators. Each is rated at 2A. Very few externalcomponents are needed for standard operation becausethe power switch, oscillator, feedback, and control circuitryare all on-chip. Employing a classic buck topology, theseregulators perform high-current step-down functions.These regulators have excellent dynamic and transientresponse 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 inputrange.
Each regulator is available in a 5-pin TO-220 package.These devices have a preset 100kHz oscillator frequencyand a preset current limit of 2.6A. See the MAX724/MAX726 data sheet for more applications information.
___________________________FeaturesoInput Range:Up to 40Vo2A On-Chip Power SwitchoFixed Outputs:5V (MAX727)
3.3V(MAX728)3V (MAX729)
o100kHz Switching Frequency
oExcellent Dynamic CharacteristicsoFew External Componentso8.5mAQuiescent CurrentoTO-220 Package
MAX727/MAX728/MAX729______________Ordering InformationPARTMAX727CCKMAX727ECKMAX728CCKMAX728ECKMAX729CCKTEMP. RANGE0°C to +70°C-40°C to +85°C0°C to +70°C-40°C to +85°C0°C to +70°CPIN-PACKAGE5 TO-2205 TO-2205 TO-2205 TO-2205 TO-220_______________________ApplicationsDistributed Power from High-Voltage Buses
High-Current, High-Voltage Step-Down ApplicationsMultiple-Output Buck Converter
MAX729ECK-40°C to +85°C5 TO-220__________Typical Operating Circuit__________________Pin ConfigurationFRONT VIEWINPUT8V TO 40V100µHOUTPUTVINV5V AT 2ASW220µFMAX727MBR745VINMAX72754VSWVCSENSEMAX728470µFMAX7293GND2VC2.7kGND1SENSE0.01µF5-PIN TO-220CASE IS CONNECTED TO GROUND. STANDARD PACKAGE HAS STAGGERED LEADS.CONTACT FACTORY FOR STRAIGHT LEADS.STEP-DOWN CONVERTER________________________________________________________________Maxim Integrated Products1
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5V/3.3V/3V 2A Step-Down, PWM,Switch-Mode DC-DC RegulatorsMAX727/MAX728/MAX729ABSOLUTE MAXIMUM RATINGS
Input Voltage..................................................45VSwitch Voltage with Respect to Input Voltage................50VSwitch Voltage with Respect to GND Pin (VSWnegative)
(Note 1).....................................................35VSENSE Pin Voltage...................................-0.3V, +10VOperating Temperature Ranges
MAX72_CCK.....................................0°C to +70°CMAX72_ECK....................................-40°C to +85°C
Junction Temperature Ranges:
MAX72_CCK....................................0°C to +125°CMAX72_ECK..................................-40°C to +125°CStorage Temperature Range...................-65°C to +160°CLead 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 functionaloperation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure toabsolute maximum rating conditions for extended periods may affect device reliability.ELECTRICAL CHARACTERISTICS
(VIN= 25V, Tj= TMINto TMAX, unless otherwise noted.)
PARAMETERInput Supply Voltage RangeSwitch-On Voltage (Note 2)Switch-Off LeakageSupply Current (Note 3)ISW= 0.5AISW= 2AVIN= 25V, VSW= 0VVIN= 40V, VSW= 0VVIN≤40V, VSENSE= 5.5VNormal ModeMinimum Supply VoltageSwitch-Current Limit (Note 5)Maximum Duty CycleTj= +25°CSwitching FrequencySwitching Frequency Line RegulationError-Amplifier Voltage Gain Error-Amplifier TransconductanceError-Amplifier Source CurrentError-Amplifier Sink CurrentVSENSE= VOUT - 10%VSENSE= VOUT + 10%8V ≤VIN≤40V1V ≤VC≤4VTj= +25°CTj= +25°CTj= +25°CTj= +25°C30001000.6Tj≤+125°CVOUT= VSENSE= 0V (Note 5)Tj= +25°CStart-Up Mode (Note 4)Tj≥0°CTj< 0°C2.0859085200.03200050001401.090002251.70.10%/VV/VµmhoµAmATj= +25°CTj= +25°C8.57.33.53.52.690100110120kHzCONDITIONSMIN8.0TYPMAX40.01.21.7150250118.04.85.03.2A%VUNITSVVµAmA2_______________________________________________________________________________________
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5V/3.3V/3V 2A Step-Down, PWM,Switch-Mode DC-DC RegulatorsELECTRICAL CHARACTERISTICS (continued)
(VIN= 25V, Tj= TMINto TMAX, unless otherwise noted.)
PARAMETER
SENSE Voltage
VC= 2V
CONDITIONS
MAX727MAX728MAX729MAX727MAX728MAX729Tj= +25°CTj= TMINtoTMAXTj= +25°CTj= TMINto TMAX
MIN4.853.202.903.02.52.2
TYP5.003.303.005.04.23.8±0.5±1.00.0051.5-4
4.0MAX5.153.403.108.07.06.5±2.0
%
±3.00.020
%/VVmV/°C°C/WUNITSV
MAX727/MAX728/MAX729SENSE Pin Divider ResistanceTj= +25°C
VOUT(nominal) = 5V (MAX727),3.3V (MAX728), or 3V (MAX729); all conditions of input voltage,output voltage, and load current8V ≤VIN≤40V0% duty cycle0% duty cycle
kΩ
Output Voltage Tolerance
Output Voltage Line RegulationVCVoltage
VCVoltage Temperature CoefficientThermal 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 VCpin 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 VINto GND must be ≥8V after start-up.
Note 5:To avoid extremely short switch-on times, the switch frequency is internally scaled down when VSENSEis less than 2.6V
(MAX727), 2.0V (MAX728), or 1.8V (MAX729). Switch current limit is tested with VSENSEadjusted to give a 1µs minimumswitch-on time.
Note 6:Guaranteed, not production tested.
______________________________________________________________Pin DescriptionPINNAMEFUNCTION
1
SENSE
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
2VC
MAX727/MAX728/MAX729. Output swing is limited to about 5.8V in the positive direction and -0.7V in the negative direction. VCcan also synchronize the MAX727/MAX728/MAX729 to anexternal TTL clock in the 115kHz to 170kHz range. See MAX724/MAX726 data sheet.
3GNDGroundrequires 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.
4VSWInternal Power Switch Output. The Switch output can swing 35V below ground and is rated for 2A.5
VIN
VINsupplies power to the internal circuitry and also connects to the collector of the internal powerswitch. VINmust be bypassed with a low-ESR capacitor, typically 200µF or 220µF.
_______________________________________________________________________________________3
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5V/3.3V/3V 2A Step-Down, PWM,Switch-Mode DC-DCRegulatorsMAX727/MAX728/MAX729________________________________________________________Package InformationEQH1φPAFDIMABC1DEeFH1J1J2J3LL1L2φPQINCHESMAXMIN0.1900.1400.0400.0150.0220.0140.6500.5600.4200.3800.067 BSC0.0550.0450.2700.2300.1150.0800.1850.1700.3350.3270.2000.1700.3400.2600.7200.7000.1610.1390.1200.100MILLIMETERSMINMAX3.564.820.381.010.410.5014.2316.519.6610.661.70 BSC1.141.395.856.852.042.924.324.708.318.514.325.086.608.6417.7818.293.544.082.543.0421-005-DL2J1LL1C1BeJ2J3INCHESMAXMIN0.1900.1400.0400.0150.0220.0140.6500.5600.4200.3800.067 BSC0.0550.0450.2700.2300.1150.0800.5800.5000.1610.1390.1200.1005-PIN TO-220(STAGGERED LEAD)PACKAGEMILLIMETERSMINMAX3.564.820.381.010.410.5014.2316.519.6610.661.70 BSC1.141.395.856.852.042.9212.7014.733.544.082.543.0421-4737-EQH1φPAFDJ1DIMABC1DEeFH1J1LφPQLBeC15-PIN TO-220(STRAIGHT LEAD)PACKAGECONTACT FACTORY FOR AVAILABILITYMaxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses areimplied. 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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