Wide Input Step Down Converter Output Current Efficiency Input Ra

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Wide Input Step Down Converter Output Current Efficiency Input Ra

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ACT4012
Wide Input Step Down Converter
Output Current Efficiency Input Range Shutdown Supply Current 410kHz 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 SOP-8 Package
GENERAL DESCRIPTION
ACT4012 current-mode step-down DC-DC converter that generates output current 410kHz switching frequency. device utilizes Active-Semi's proprietary ISOBCD20 process operation with input voltage 20V. Consuming only shutdown mode, ACT4012 highly efficient with peak efficiency when operation. Protection features include cycle-by-cycle current limit, thermal shutdown, frequency foldback short circuit. ACT4012 available SOP-8 package requires very external devices operation.
APPLICATIONS
Monitors Portable DVDs Car-Powered Battery-Powered Equipments Set-Top Boxes Telecom Power Supplies Cable Modems Routers Termination Supplies
2.5V/2A
ACT4012
ENABLE COMP
Figure Typical Application Circuit
Active-Semi, Inc.
www.active-semi.com
ACT4012
ORDERING INFORMATION
PART NUMBER ACT4012SH ACT4012SH-T TEMPERATURE RANGE -40°C 85°C -40°C 85°C PACKAGE SOP-8 SOP-8 PINS PACKING TUBE TAPE REEL
CONFIGURATION
COMP
ACT4012SH
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 Heatsink. 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. This small internal pull current high level voltage when connected. allow exceed Connected.
Active-Semi, Inc.
www.active-semi.com
ACT4012
ABSOLUTE MAXIMUM RATINGS
(Note: Exceeding these limits damage device. Exposure absolute maximum rating conditions long periods affect device reliability.)
PARAMETER Supply Voltage Voltage Voltage COMP Voltage Continuous Current Junction Ambient Thermal Resistance Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, sec)
VALUE -0.3 -0.3 Internally limited 0.76
UNIT °C/W
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
SYMBOL TEST CONDITIONS VOUT ILOAD 4.75V 20V, VCOMP 1.5V RONH RONL ILIM GCOMP AVEA DMAX ICOMP ±10µA
1.267
1.293 2.85 4000
1.319
UNIT µA/V
1.1V 1.4V Hysteresis 0.1V pulled 4.5V typically when left unconnected 1.4V Hysteresis 10°C
Active-Semi, Inc.
www.active-semi.com
ACT4012
ENABLE REGULATOR REFERENCE CURRENT SENSE AMPLIFIER
COMP
ERROR AMPLIFIER
1.293V
COMPARATOR
HIGH-SIDE POWER SWITCH
FOLDBACK CONTROL
OSCILLATOR RAMP
LOGIC LOW-SIDE POWER SWITCH THERMAL SHUTDOWN
Figure Functional Block Diagram
FUNCTIONAL DESCRIPTION
seen Figure Functional Block Diagram, ACT4012 current mode pulse width modulation (PWM) converter. converter operates follows: switching cycle starts when rising edge Oscillator clock output causes HighSide 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 LowSide 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 2.55V. Oscillator normally switches 410kHz. However, voltage less than 0.7V, then switching frequency decreases until reaches minimum 50kHz 0.5V.
SHUTDOWN CONTROL
ACT4012 enable input turning off. When less than 0.7V, current shutdown mode output discharged through LowSide Power Switch. When higher than 1.3V, normal operation mode. internally pulled with current source left unconnected always-on operation. Note that voltage input with maximum voltage should never directly connected
THERMAL SHUTDOWN
ACT4012 automatically turns when junction temperature exceeds 160°C.
Active-Semi, Inc.
www.active-semi.com
ACT4012
APPLICATION INFORMATION
OUTPUT VOLTAGE SETTING
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
ACT4012
Figure 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:
RFB1 1.293
OUTPUT CAPACITOR
output capacitor also needs have keep output voltage ripple. output ripple voltage
VRIPPLE OUTMAX RIPPLE
LCOUT
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 IOUTMAX 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 (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
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.
VOUT
1.5V
1.8V
2.5V
3.3V
6.8H 6.8H
Active-Semi, Inc.
www.active-semi.com
ACT4012
STABILITY COMPENSATION
COMP
STEP zero cross over frequency. RCOMP less than 15k, equation CCOMP
CCOMP
ACT4012
RCOMP
(10)
RCOMP limited 15k, then actual cross over frequency (VOUTCOUT). Therefore: CCOMP VOUT COUT (11)
*CCOMP2 needed only high output capacitor
Figure Stability Compensation
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
ESRCOUT
AVDC
1.3V AVEAGCOMP IOUT
dominant pole CCOMP:
AVEA CCOMP
,0.012 VOUT
(12)
proper value CCOMP2
CCOMP COUT RESRCOUT RCOMP
second pole output pole:
IOUT 2VOUT COUT
(13)
first zero RCOMP CCOMP:
2RCOMP CCOMP
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 Typical Compensation Different Output Voltages Output Capacitors
finally, third pole RCOMP CCOMP2 CCOMP2 used):
2RCOMP CCOMP
Follow following steps compensate
STEP cross over frequency 1/10 switching frequency RCOMP:
RCOMP VOUT COUT COMP 1.3V
VOUT COUT
VOUT 2.5V 3.3V 2.5V 3.3V 2.5V 3.3V
COUT RCOMP Ceramic 8.2k Ceramic Ceramic 470F/6.3V/30m 470F/6.3V/30m 470F/10V/30m
CCOMP 2.2nF 1.5nF 1.5nF 1.5nF 1.8nF 2.7nF 15nF 22nF 27nF
CCOMP2 None None None None None None None
limit RCOMP maximum.
Figure shows sample ACT4012 application circuit generating 2.5V/2A output.
Active-Semi, Inc.
www.active-semi.com
ACT4012
10nF H/3A 2.5V/2A
IC1* ACT4012
ENABLE
COMP 2.2nF 8.2k (OPTIONAL) 22F/10V Ceramic
10F/25V
*Heat dissipation copper area required. Leave more than uncovered area immediately adjacent pin.
Figure ACT4012 2.5V/2A Output Application
Active-Semi, Inc.
www.active-semi.com
ACT4012
TYPICAL PERFORMANCE CHARACTERISTICS
(Circuit Figure unless otherwise specified
Active-Semi, Inc.
www.active-semi.com
ACT4012
PACKAGE OUTLINE
SOP-8 PACKAGE OUTLINE DIMENSIONS
DIMENSION MILLIMETERS 1.350 1.750 0.100 0.250 1.350 1.550 0.330 0.510 0.190 0.250 4.780 5.000 3.800 4.000 5.800 6.300 1.270 0.400 1.270 DIMENSION INCHES 0.053 0.069 0.004 0.010 0.053 0.061 0.013 0.020 0.007 0.010 0.188 0.197 0.150 0.157 0.228 0.248 0.050 0.016 0.050
SYMBOL
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 data sheet, does convey patent license. Active-Semi logo trademarks Active-Semi, Inc. more information this other products, contact sales@active-semi.com visit www.active-semi.com. other inquiries, please send 1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044,
Active-Semi, Inc.
www.active-semi.com

Wide Input Step Down Converter Output Current Efficiency Input Ra

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