12/2006 Wide Input Step Down Converter FEATURES Output Curre
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ACT4070
12/2006
Wide Input Step Down Converter FEATURES
Output Current Efficiency 4.5V Input Range Shutdown Supply Current 400kHz Switching Frequency Adjustable Output Voltage Cycle-by-Cycle Current Limit Protection Thermal Shutdown Protection Internal Soft Start Function Frequency Fold Back Short Circuit Stability with Wide Range Capacitors, Including Ceramic Capacitors
GENERAL DESCRIPTION
ACT4070 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, ACT4070 highly efficient with peak efficiency when operation. Protection features include cycle-by-cycle current limit, thermal shutdown, frequency fold back short circuit. device also includes internal soft start function prevent overshoot. ACT4070 available SOP-8/EP exposed package requires very external devices operation.
SOP-8/EP (Exposed Pad) 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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ACT4070
ORDERING INFORMATION
PART NUMBER
ACT4070YH ACT4070YH-T
TEMPERATURE RANGE
-40°C 85°C -40°C 85°C
PACKAGE
SOP-8/EP SOP-8/EP
PINS
PACKING
TUBE TAPE REEL
CONFIGURATION
SOP-8/EP
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 Technique Application Information section. Enable Input. When higher than 1.3V, this turns When lower than 0.7V, this turns off. Output voltage discharged when off. This small internal pull current high level voltage when connected. Connected. Exposed shown dashed box. exposed thermal should connected board ground plane ground plane should include large exposed copper under package thermal dissipation (see package outline). leads exposed should flush with board, without offset from board surface.
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ACT4070
ABSOLUTE MAXIMUM RATINGS
PARAMETER
COMP Continuous Current Junction Ambient Thermal Resistance (JA) Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, sec)
VALUE
-0.3 -0.3 -0.3 -0.3 Internally limited
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
VOUT 2.5V, ILOAD
UNIT
µA/V
1.198 1.222 1.246 12V, ILOAD/ICOMP ICOMP ±10µA 4000 0.85
ILIM GCOMP AVEA
DMAX
1.1V, mode 1.4V, mode Hysteresis 0.1V pulled when left unconnected switching Hysteresis 10°C
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ACT4070
FUNCTIONAL BLOCK DIAGRAM
FUNCTIONAL DESCRIPTION
seen Functional Block Diagram, ACT4070 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 2.65V. Oscillator normally switches 400kHz. However, voltage less than 0.7V, then switching frequency decreases until reaches typical value 40kHz
Shutdown Control
ACT4070 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
ACT4070 automatically turns when junction temperature exceeds 160°C then restarts once temperature falls 150°C.
Copyright 2006 Active-Semi, Inc. www.active-semi.com
ACT4070
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 traces possible. 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
VRIPPLE IOUTMAX RIPPLE RRIPPLE LCOUT
VOUT VOUT IOUTMAX RIPPLE
where input voltage, VOUT output voltage, switching frequency, IOUTMAX maximum output current, KRIPPLE ripple factor. Typically, choose KRIPPLE between correspond peak-to-peak ripple current being percentage maximum output current. With this inductor value (Table peak inductor current IOUT KRIPPLE Make sure that this peak inductor current less that current limit. Finally, select inductor core size that does saturate Table Typical Inductor Values VOUT
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. case tantalum electrolytic type, ripple dominated RESR multiplied ripple current. that case, output capacitor chosen have sufficiently ESR. ceramic output type, typically choose capacitance about 22µF. tantalum electrolytic type, choose capacitor with less than ESR.
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
6.8H
3.3V
8.5H
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ACT4070
Stability compensation
Figure Stability Compensation STEP zero cross over frequency. RCOMP less than 15k, equation CCOMP
CCOMP
RCOMP
(10)
RCOMP limited 15k, then actual cross over frequency 4.8/(VOUTCOUT). Therefore:
CCOMP VOUT COUT
CCOMP2 needed only high output capacitor
(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
RESROUT 1.1x10 ,0.012VOUT
proper value CCOMP2 (12)
AVDC
1.222V AVEAGCOMP IOUT
dominant pole CCOMP:
COMP
CCOMP
COUT ESROUT RCOMP
(13)
second pole output pole:
IOUT VOUT
Though CCOMP2 unnecessary when output capacitor sufficiently ESR, small value CCOMP2 such 220pF improve stability against layout parasitic effects. Table shows some calculated results based compensation method above.
first zero RCOMP CCOMP:
RCOMP CCOMP
Table Typical Compensation Different Output Voltages Output Capacitors VOUT COUT
Ceramic Ceramic Ceramic 100F 100F 100F
finally, third pole RCOMP CCOMP2 CCOMP2 used):
RCOMP CCOMP2
RCOMP
5.6k
CCOMP CCOMP2
3.3nF 3.3nF 1.5nF 1.5nF 2.2nF 4.7nF 220pF 220pF 220pF 220pF 220pF 220pF
1.8V 2.5V
Follow following steps compensate STEP cross over frequency 1/10 switching frequency RCOMP:
1.8V 2.5V
RCOMP
VOUT COUT GEAGCOMP .222
VOUT COUT
CCOMP2 needed board parasitic high output capacitor.
limit RCOMP maximum.
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Figure shows sample ACT4070 application circuit generating 2.5V/3A output.
Copyright 2006 Active-Semi, Inc. www.active-semi.com
ACT4070
Figure ACT4070 2.5V/3A Output Application
4.5V ENABLE
10nF
10µH/4A
2.5V/3A VOUT
ACT4070
(CCOMP) 3.3nF (RCOMP) 5.6k
COMP (COUT) 22µF/10V ceramic 47µH/6.3
10µF/35V
(CCOMP2) 220pF
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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ACT4070
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit Figure unless otherwise specified.)
Efficiency Output Current
ACT4070-0001
Efficiency Output Current
ACT4070-0002
Efficiency
0.01
Efficiency
VOUT 2.5V 10µH 22µF COUT 22µF
VOUT 15µH 22µF COUT 22µF
0.01
Output Current
Output Current
Feedback Voltage Temperature
1.27
Switching Frequency Input Voltage
ACT4070-0004
1.25
Switching Frequency (kHz)
ACT4070-0003
Feedback Voltage
1.23
1.21 1.19 1.17
Temperature (°C)
Input Voltage
Shutdown Supply Current Input Voltage
Surface Temperature Output Current
ACT4070-006 VOUT 15µH 22µF COUT 22µF
ACT4070-0005
Shutdown Supply Current (µA)
Surface Temperature (°C)
Input Voltage
Output Current
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ACT4070
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit Figure unless otherwise specified.)
Load Transient Response
ACT4070-0007
Load Transient Response
ACT4070-0008
VOUT 200mV/div
VOUT 200mV/div
IOUT
IOUT
100µs/div
100µs/div
Load Transient Response
ACT4070-0009
VOUT 200mV/div
IOUT
100µs/div
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ACT4070
PACKAGE OUTLINE
SOP-8/EP PACKAGE OUTLINE DIMENSIONS
SYMBOL
DIMENSION MILLIMETERS 1.750 0.150 1.550 0.510 0.250 5.100 3.402 4.000 6.200 2.513
DIMENSION INCHES 0.053 0.002 0.053 0.013 0.007 0.185 0.126 0.150 0.228 0.091 0.069 0.006 0.061 0.020 0.010 0.200 0.134 0.157 0.244 0.099
1.350 0.050 1.350 0.330 0.170 4.700 3.202 3.800 5.800 2.313
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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