Wide Input 1.5A Step Down Converter FEATURES 1.5A Output Current
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ACT4012A
Wide Input 1.5A Step Down Converter FEATURES
1.5A Output Current Efficiency Input Range 10µA Shutdown Supply Current 420kHz 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
ACT4012A current-mode step-down DC/DC converter that generates 1.5A output 420kHz switching frequency. device utilizes Active-Semi's proprietary ISOBCD20 process operation with input voltages 20V. Consuming only 10µA shutdown mode, ACT4012A highly efficient with peak efficiency when operation. Protection features include cycle-by-cycle current limit, thermal shutdown, frequency foldback short circuit. ACT4012A available SOP-8 package requires very external devices operation.
SOP-8 Package
APPLICATIONS
Monitors Portable DVDs Car-Powered Battery-Powered Equipments S-Top Boxes Telecom Power Supplies Cable Modems Routers Termination Supplies
TYPICAL APPLICATION CIRCUIT
5V/1.5A
ACT4012A
ENABLE COMP
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ACT4012A
ORDERING INFORMATION
PART NUMBER
ACT4012ASH ACT4012ASH-T
TEMPERATURE RANGE
-40°C 85°C -40°C 85°C
PACKAGE
SOP-8 SOP-8
PINS
PACKING
TUBE TAPE REEL
CONFIGURATION
ACT4012ASH
COMP
SOP-8
DESCRIPTIONS
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 Heat sink. Connect large, uncovered copper area best heat dissipation. Feedback Input. voltage this regulated 1.293V. 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. small internal pull-up current when connected. Connected.
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ACT4012A
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 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-Up Current Supply Current Shutdown Supply Current Operation Thermal Shutdown Temperature
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SYMBOL
RONH RONL
TEST CONDITIONS
VOUT ILOAD 1.5A 4.75V
1.261
1.293 13.5
1.325
UNIT
ILIM GCOMP AVEA DMAX 1.1V ICOMP ±10µA
4000
µA/V
Hysteresis 0.1V pulled when left unconnected 1.4V Hysteresis 10°C
0.85
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ACT4012A
FUNCTIONAL BLOCK DIAGRAM
ENABLE REGULATOR REFERENCE
CURRENT SENSE AMPLIFIER
COMP ERROR AMPLIFIER 1.293V
COMP
HIGH-SIDE POWER SWITCH
FOLDBACK CONTROL
OSCILLATOR RAMP
LOGIC LOW-SIDE POWER SWITCH
THERMAL SHUTDOWN
FUNCTIONAL DESCRIPTION
seen Functional Block Diagram, ACT4012A 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 positive rail. This charged when Low-Side Power Switch turns
COMP voltage integration error between input internal 1.293V reference. lower than reference voltage, COMP tends higher increase current output. Current limit happens when COMP reaches maximum clamp value 2.6V. Oscillator normally switches 420kHz. However, voltage less than 0.7V, then switching frequency decreases until reaches minimum 50kHz 0.5V.
Shutdown Control
ACT4012A enable input turning off. When less than 0.7V, 10µA 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. Note that high voltage input that with stand voltages VIN.
Thermal Shutdown
ACT4012A automatically turns when junction temperature exceeds 160°C.
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ACT4012A
APPLICATIONS INFORMATION
Output Voltage Setting
Figure Output Voltage Setting
VOUT ACT4012A RFB2 RFB1
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
Figure shows connections setting output voltage. Select proper ratio feedback resistors RFB1 RFB2 based output voltage. Typically, RFB2 determine RFB1 from output voltage:
Output Capacitor
output capacitor also needs have keep output voltage ripple. output ripple voltage
VRIPPLE IOUTMAX RIPPLE RESR
1.293V
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:
VOUT VOUT OUTMAX RIPPLE
where input voltage, VOUT output voltage, switching frequency, IOUTMAX maximum output current, KRIPPLE ripple factor. Typically, choose KRIPPLE correspond peak-to-peak ripple current being maximum output current. With this inductor value, peak inductor current IOUT KRIPPLE/2). Make sure that this peak inductor current less that current limit. Finally, select inductor core size that does saturate Table Typical Inductor Values
VOUT 1.5V 7.5µH 1.8V 10µH 2.5V 12µH 3.3V 15µH 22µH
where IOUTMAX maximum output current, KRIPis 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.
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ACT4012A
STABILITY COMPENSATION
Figure Stability Compensation
STEP zero cross over frequency. RCOMP less than 15k, equation CCOMP
COMP COMP
(10)
COMP ACT4012A CCOMP
CCOMP2
RCOMP limited 15k, then actual cross over frequency (VOUTCOUT). Therefore:
CCOMP VOUTCOUT
(11)
RCOMP
CCOMP2 needed only high output capacitor
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
RESRCOUT ,0.012 VOUT
proper value CCOMP2
(12)
AVDC
AVEA GCOMP
dominant pole CCOMP: AVEA COMP second pole output pole:
VOUT
CCOMP2
COUT RESRCOUT RCOMP
(13)
Though CCOMP2 unnecessary when output capacitor sufficiently ESR, small value CCOMP2 such 100pF improve stability against layout parasitic effects. Table shows some calculated results based compensation method above. Table
first zero RCOMP CCOMP:
2RCOMP CCOMP2
Typical Compensation Different Output Voltages Output Capacitors VOUT
2.5V 3.3V 2.5V 3.3V 2.5V 3.3V
finally, third pole RCOMP CCOMP2 CCOMP2 used):
COMP COMP2
COUT
22µF Ceramic 22µF Ceramic 22µF Ceramic 47µF 47µF 47µF 470µF/6.3V/30m 470µF/6.3V/30m 470µF/6.3V/30m
RCOMP
CCOMP CCOMP2
1.5nF 1.5nF 1.5nF 1.5nF 1.8nF 2.7nF 15nF 22nF 27nF None None None None None None None
Follow following steps compensate STEP cross over frequency 1/10 switching frequency RCOMP:
COMP
VOUT GCOMP
CCOMP2 needed high output capacitor. Figure shows example ACT4012A application circuit generating 5V/1.5A output.
limit RCOMP maximum.
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ACT4012A
Rev0, 16-May-08 Figure ACT4012A 5V/1.5A Output Application
7.5V
10nF
22µH/2A 5V/1.5A
VOUT
ACT4012A
ENABLE COMP 1.5nF (OPTIONAL)
10µF/
22µF/10V Ceramic
30V, Schottky diode with forward voltage, 20BQ030 SK23 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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ACT4012A
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit Figure unless otherwise specified.)
Efficiency Load
ACT4012A-001
Efficiency Load
ACT4012A-002
Efficiency
VOUT 22µH COUT 22µF/cera
Efficiency
VOUT 3.3V 15µH COUT 22µF/cera
Load
Load
Surface Temperature Load
ACT4012A-003
Output Voltage Input Voltage
ACT4012A-004 IOUT 0.5A
Surface Temperature (°C)
Output Voltage
IOUT IOUT 1.5A
Load
Input Voltage
Feedback Voltage Junction Temperature
Shutdown Supply current (µA)
1.30 ACT4012A-005
Shutdown Supply current Input Voltage
ACT4012A-006
Feedback Voltage
1.29
1.28
1.27
1.26
Junction Temperature (°C)
Input Voltage
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ACT4012A
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit Figure unless otherwise specified.)
Switching Frequency Input Voltage
ACT4012A-007
Switching Frequency (kHz)
Input Voltage
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ACT4012A
PACKAGE OUTLINE
SOP-8 PACKAGE OUTLINE DIMENSIONS
SYMBOL
DIMENSION MILLIMETERS
1.350 0.100 1.350 0.330 0.190 4.700 3.800 5.800
DIMENSION INCHES
0.053 0.004 0.053 0.013 0.007 0.185 0.150 0.228
1.750 0.250 1.550 0.510 0.250 5.100 4.000 6.300
0.069 0.010 0.061 0.020 0.010 0.201 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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