12/2006 Wide Input Step Down Converter FEATURES Output Curre
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ACT4072
12/2006
Wide Input Step Down Converter FEATURES
Output Current Efficiency Input Range Shutdown Supply Current 400kHz Switching Frequency Adjustable Output Voltage Cycle-by-Cycle Current Limit Protection Thermal Shutdown Protection Frequency FoldBack Short Circuit Stability with Wide Range Capacitors, Including Ceramic Capacitors
GENERAL DESCRIPTION
ACT4072 current-mode step-down DC/DC converter that generates output current 400kHz switching frequency. device utilizes Active-Semi's proprietary ISOBCD30 process operation with input voltage 30V. Consuming only shutdown mode, ACT4072 highly efficient with peak efficiency when operation. Protection features include cycle-by-cycle current limit, thermal shutdown, frequency foldback short circuit. ACT4072 available SOP-8 package requires very external devices operation.
SOP-8 Package
APPLICATIONS
Monitors Televisions HDTV Portable Players Car-Powered Battery-Powered Equipment Set-Top Boxes Telecom Power Supplies Cable Modems Routers
TYPICAL APPLICATION CIRCUIT
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ACT4072
ORDERING INFORMATION
PART NUMBER
ACT4072SH ACT4072SH-T
TEMPERATURE RANGE
-40°C 85°C -40°C 85°C
PACKAGE
SOP-8 SOP-8
PINS
PACKING
TUBE TAPE REEL
CONFIGURATION
SOP-8
DESCRIPTION
NUMBER
NAME
COMP
DESCRIPTION
Bootstrap. This acts positive rail high-side switch's gate driver. Connect 10nF between this Input Supply. Bypass this with capacitor. Input Capacitor Application Information section. Switch Output. Connect this switching inductor. Ground. Feedback Input. voltage this regulated 1.222V. Connect resistor divider between output ground output voltage. Compensation Pin. Compensation Techniques Application Information section. Enable Input. Drive higher than 1.3V leave unconnected enable Drive lower than 0.7V disable When disabled, current shutdown mode output discharged through Low-Side Power Switch. This small internal pull current high level voltage when connected. Connected.
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ACT4072
ABSOLUTE MAXIMUM RATINGS
PARAMETER
COMP Continuous Current Junction Ambient Thermal Resistance (JA) Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, sec) Ambient Operating Temperature
VALUE
-0.3 -0.3 -0.3 -0.3 Internally limited 0.76
UNIT
°C/W
exceed these limits prevent damage device. Exposure absolute maximum rating conditions long periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN 12V, 25°C, unless otherwise specified.)
PARAMETER
Input Voltage Feedback Voltage High-Side Switch Resistance Low-Side Switch Resistance Leakage Current Limit COMP Current Limit Transconductance Error Amplifier Transconductance Error Amplifier Gain Switching Frequency Short Circuit Switching Frequency Maximum Duty Cycle Minimum Duty Cycle Enable Threshold Voltage Enable Pull Current Supply Current Shutdown Supply Current Operation Thermal Shutdown Temperature
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SYMBOL
RONH RONL
TEST CONDITIONS
UNIT
µA/V
1.198
1.222 0.13
1.246
ILIM GCOMP AVEA DMAX DMIN 1.1V, mode 1.4V, mode Hysteresis 0.1V ICOMP ±10µA
4000
switching Hysteresis 10°C
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ACT4072
FUNCTIONAL BLOCK DIAGRAM
FUNCTIONAL DESCRIPTION
seen Functional Block Diagram, ACT4072 current mode pulse width modulation (PWM) converter. converter operates follows: switching cycle starts when rising edge Oscillator clock output causes High-Side Power Switch turn Low-Side Power Switch turn off. With side inductor connected inductor current ramps store energy magnetic field. inductor current level measured Current Sense Amplifier added Oscillator ramp signal. resulting summation higher than COMP voltage, output Comparator goes high. When this happens when Oscillator clock output goes low, High-Side Power Switch turns Low-Side Power Switch turns this point, side inductor swings diode voltage below ground, causing inductor current decrease magnetic energy transferred output. This state continues until cycle starts again. High-Side Power Switch driven logic using bootstrap positive rail. This charged when Low-Side Power Switch turns
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COMP voltage integration error between input internal 1.222V reference. lower than reference voltage, COMP tends higher increase current output. Current limit happens when COMP reaches maximum clamp value 2.55V. Oscillator normally switches 400kHz. However, voltage less than 0.7V, then switching frequency decreases until reaches minimum 60kHz 0.5V.
Shutdown Control
ACT4072 enable input turning off. When less than 0.7V, current shutdown mode output discharged through Low-Side Power Switch. When higher than 1.3V, normal operation mode. internally pulled with current source left unconnected always-on operation.
Thermal Shutdown
ACT4072 automatically turns when junction temperature exceeds 160°C.
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ACT4072
APPLICATIONS INFORMATION
Output Voltage Setting
Figure shows connections setting output voltage. Select proper ratio feedback resistors RFB1 RFB2 based output voltage. Typically, RFB2 determine RFB1 from output voltage:
Input Capacitor
input capacitor needs carefully selected maintain sufficiently ripple supply input converter. capacitor highly recommended. Since large current flows this capacitor during switching, also affects efficiency. input capacitance needs higher than 10µF. best choice ceramic type, however, tantalum electrolytic types also used provided that ripple current rating higher than output current. input capacitor should placed close pins with shortest possible traces. case tantalum electrolytic types, they further away small parallel 0.1µF ceramic capacitor placed right next
RFB1 RFB2 1.222V
Figure Output Voltage Setting
Output Capacitor Inductor Selection
inductor maintains continuous current output load. This inductor current ripple that dependent inductance value: higher inductance reduces peak-to-peak ripple current. trade high inductance value increase inductor core size series resistance, reduction current handling capability. general, select inductance value based ripple current requirement: output capacitor also needs have keep output voltage ripple. output ripple voltage
RRIPPLE LOUTMAX RIPPLE RESR
28fSW LCOUT
VOUT VOUT IOUTMAXK RIPPLE
where IOUTMAX maximum output current, KRIPPLE ripple factor, RESR resistance output capacitor, switching frequency, inductor value, COUT output capacitance. case ceramic output capacitors, RESR very small does contribute ripple. Therefore, lower capacitance value used ceramic type, typically choose capacitance about 22µF. case tantalum electrolytic type, ripple dominated RESR multiplied ripple current. that case, output capacitor chosen have sufficiently ESR, typically choose capacitor with less than ESR.
where input voltage, VOUT output voltage, switching frequency, IOUTMAX maximum output current, KRIPPLE ripple factor. Typically, choose KRIPPLE corresponding peak-to-peak ripple current being maximum output current. With this inductor value (Table peak inductor current IOUT KRIPPLE Make sure that this peak inductor current less that 2.4A current limit. Finally, select inductor core size that does saturate 2.4A. Table Typical Inductor Values VOUT
Rectifier Diode
Schottky diode rectifier conduct current when High-Side Power Switch off. Schottky diode must have current rating higher than maximum output current reverse voltage rating higher than maximum input voltage.
1.5V
6.8H
1.8V
6.8H
2.5V
3.3V
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ACT4072
Stability compensation
Figure Stability Compensation STEP zero cross over frequency. RCOMP less than 15k, equation CCOMP
COMP
COMP
(10)
RCOMP limited 15k, then actual cross over frequency 3.4/(VOUTCOUT). Therefore:
CCOMP 5VOUTCOUT
CCOMP2 needed only high output capacitors parasitics
(11)
feedback system stabilized components COMP pin, shown Figure loop gain system determined following equation:
STEP output capacitor's high enough cause zero lower than times cross over frequency, additional compensation capacitor CCOMP2 required. condition using CCOMP2
AVDC
1.222V AVEAGCOMP IOUT
1.1x10 ,0.012VOUT ESROUT
proper value CCOMP2
(12)
dominant pole CCOMP:
AVEA CCOMP
CCOMP2
COUT RESROUT RCOMP
(13)
second pole output pole:
small value CCOMP2 such 100pF improve stability against layout parasitic effects. Table shows some calculated results based compensation method above. Table Typical Compensation Different Output voltages Output Capacitors VOUT
2.5V 3.3V
IOUT VOUTCOUT RCOMP CCOMP
first zero RCOMP CCOMP:
finally, third pole RCOMP CCOMP2 CCOMP2 used):
COUT
Ceramic Ceramic Ceramic 470µF/6.3V/30m 470µF/6.3V/30m 470µF/6.3V/30m
RCOMP CCOMP CCOMP2
8.2k 2.2nF 1.5nF 1.5nF 1.5nF 1.8nF 2.7nF 15nF 22nF 27nF 100pF 100pF 100pF 100pF 100pF 100pF
RCOMPCCOMP2
2.5V 3.3V 2.5V 3.3V
Follow following steps compensate STEP cross over frequency 1/10 switching frequency RCOMP:
RCOMP
VOUT COUT 10GEAGCOMP 1.222V
VOUT COUT
limit RCOMP maximum.
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CCOMP2 needed board parasitic high output capacitor.
Figure shows example ACT4072 application circuit generating 5V/2A output.
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ACT4072
Figure ACT4072 5V/2A Output Application
ENABLE
ACT4072 COMP
10nF
22µH/3A 39.2k
5V/2A VOUT
10µF/35V
1.5nF 1.5k
100pF
12.1k
22µF/10V ceramic 47µH/6.3
40V, Schottky diode with forward voltage, 30BQ040 SK34 equivalent. either ceramic capacitor (Panasonic ECJ-3YB1C226M) SP-CAP (Specialty Polymer) Aluminum Electrolytic Capacitor such Panasonic EEFCD0J470XR. SP-Cap based aluminum electrolytic capacitor technology, uses solid polymer electrolyte very stable capacitance characteristics both operating temperature frequency compared ceramic, polymer, tantalum capacitors.
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ACT4072
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit Figure unless otherwise specified.)
Efficiency Output Current
ACT4072-0001
Efficiency Output Current
ACT4072-0002
Efficiency
Efficiency
0.01
VOUT 22µH 10µF COUT 22µF
VOUT 3.3V 15µH 10µF COUT 22µF
0.01
Output Current
Output Current
Switching Frequency Input Voltage Shutdown Supply Current (mA)
ACT4072-0003
Shutdown Supply Current Input Voltage
ACT4072-0004
Switching Frequency(kHz)
Temperature (°C)
Input Voltage
Surface Temperature Output Current
1.27 ACT4072-0005
Feedback Voltage Temperature
ACT4072-006
Surface Temperature (°C)
Feedback Voltage
VOUT=5V L=22µH CIN=10µF COUT=22µF
1.25
1.23
1.21
1.19
1.17
Output Current
Temperature (°C)
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ACT4072
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit Figure unless otherwise specified.)
Load Transient Response
ACT4072-0007
Load Transient Response
ACT4072-0008
VOUT 200mV/div
VOUT 200mV/div
IOUT IOUT
100µs/div
100µs/div
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ACT4072
PACKAGE OUTLINE
SOP-8 PACKAGE OUTLINE DIMENSIONS
SYMBOL
DIMENSION MILLIMETERS
1.350 0.100 1.350 0.330 0.190 4.780 3.800 5.800
DIMENSION INCHES
0.053 0.004 0.053 0.013 0.007 0.188 0.150 0.228
1.750 0.250 1.550 0.510 0.250 5.000 4.000 6.300
0.069 0.010 0.061 0.020 0.010 0.197 0.157 0.248
1.270 0.400 1.270
0.050 0.016 0.050
Active-Semi, Inc. reserves right modify circuitry specifications without notice. Users should evaluate each product make sure that suitable their applications. Active-Semi products intended authorized critical components life-support devices systems. Active-Semi, Inc. does assume liability arising product circuit described this datasheet, does convey patent license. Active-Semi logo trademarks Active-Semi, Inc. more information this other products, contact sales@active-semi.com visit http://www.active-semi.com. other inquiries, please send 1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044,
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