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| ACT4072 Rev 1, 12/2006 Wide Input 2A Step Down Converter FEATURES 2A Output Current Up to 95% Efficiency Up to 30V Input Range 6A Shutdown Supply Current 400kHz Switching Frequency Adjustable Output Voltage Cycle-by-Cycle Current Limit Protection Thermal Shutdown Protection Frequency FoldBack at Short Circuit Stability with Wide Range of Capacitors, Including Low ESR Ceramic Capacitors GENERAL DESCRIPTION The ACT4072 is a current-mode step-down DC/DC converter that generates up to 2A output current at 400kHz switching frequency. The device utilizes Active-Semi's proprietary ISOBCD30 process for operation with input voltage up to 30V. Consuming only 6A in shutdown mode, the ACT4072 is highly efficient with peak efficiency at 95% when in operation. Protection features include cycle-by-cycle current limit, thermal shutdown, and frequency foldback at short circuit. The ACT4072 is available in SOP-8 package and requires very few external devices for operation. SOP-8 Package APPLICATIONS TFT LCD Monitors or Televisions and HDTV Portable DVD Players Car-Powered or Battery-Powered Equipment Set-Top Boxes Telecom Power Supplies DSL and Cable Modems and Routers TYPICAL APPLICATION CIRCUIT Innovative Products. Active Solutions. -1- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4072 ORDERING INFORMATION PART NUMBER ACT4072SH ACT4072SH-T TEMPERATURE RANGE -40C to 85C -40C to 85C PACKAGE SOP-8 SOP-8 PINS 8 8 PACKING TUBE TAPE & REEL PIN CONFIGURATION SOP-8 PIN DESCRIPTION PIN NUMBER 1 2 3 4 5 6 PIN NAME BS IN SW G FB COMP PIN DESCRIPTION Bootstrap. This pin acts as the positive rail for the high-side switch's gate driver. Connect a 10nF between this pin and SW. Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in Application Information section. Switch Output. Connect this pin to the switching end of the inductor. Ground. Feedback Input. The voltage at this pin is regulated to 1.222V. Connect to the resistor divider between the output and ground to set output voltage. Compensation Pin. See Compensation Techniques in Application Information section. Enable Input. Drive higher than 1.3V or leave unconnected to enable the IC. Drive lower than 0.7V to disable the IC. When disabled, the IC is in 6A low current shutdown mode and the output is discharged through the Low-Side Power Switch. This pin has a small internal pull up current to a high level voltage when pin is not connected. Not Connected. 7 EN 8 N/C Innovative Products. Active Solutions. -2- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4072 ABSOLUTE MAXIMUM RATINGS PARAMETER IN to G EN to G SW to G BS to SW FB, COMP to G Continuous SW Current Junction to Ambient Thermal Resistance (JA) Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, 10 sec) Ambient Operating Temperature VALUE -0.3 to +34 -0.3 to VIN + 0.3 -1 to VIN + 1 -0.3 to +8 -0.3 to +6 Internally limited 105 0.76 -40 to 150 -55 to 150 300 -40 to 85 UNIT V V V V V A C/W W C C C C : Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rating conditions for long periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = 12V, TA= 25C, unless otherwise specified.) PARAMETER Input Voltage Feedback Voltage High-Side Switch On Resistance Low-Side Switch On Resistance SW Leakage Current Limit COMP to Current Limit Transconductance Error Amplifier Transconductance Error Amplifier DC Gain Switching Frequency Short Circuit Switching Frequency Maximum Duty Cycle Minimum Duty Cycle Enable Threshold Voltage Enable Pull Up Current Supply Current in Shutdown IC Supply Current in Operation Thermal Shutdown Temperature Innovative Products. Active Solutions. SYMBOL VIN VFB RONH RONL TEST CONDITIONS MIN 4.5 TYP MAX UNIT 30 V V 10 4.2 A A A/V A/V V/V 460 kHz kHz % % 1.3 V A 20 2 A mA C VIN = 12V 1.198 1.222 0.13 10 1.246 VEN = 0 ILIM GCOMP GEA AVEA fSW VFB = 0 DMAX DMIN VFB = 1.1V, PWM mode VFB = 1.4V, PFM mode Hysteresis = 0.1V 0.7 340 ICOMP = 10A 2.4 0 3.3 2 550 4000 400 60 88 0 1 2 VEN = 0 VEN = 3V, not switching Hysteresis = 10C -3- 6 0.8 160 www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4072 FUNCTIONAL BLOCK DIAGRAM FUNCTIONAL DESCRIPTION As seen in the Functional Block Diagram, the ACT4072 is a current mode pulse width modulation (PWM) converter. The converter operates as follows: A switching cycle starts when the rising edge of the Oscillator clock output causes the High-Side Power Switch to turn on and the Low-Side Power Switch to turn off. With the SW side of the inductor now connected to IN, the inductor current ramps up to store energy in its magnetic field. The inductor current level is measured by the Current Sense Amplifier and added to the Oscillator ramp signal. If the resulting summation is higher than the COMP voltage, the output of the PWM Comparator goes high. When this happens or when Oscillator clock output goes low, the High-Side Power Switch turns off and the Low-Side Power Switch turns on. At this point, the SW side of the inductor swings to a diode voltage below ground, causing the inductor current to decrease and magnetic energy to be transferred to the output. This state continues until the cycle starts again. The High-Side Power Switch is driven by logic using the BS bootstrap pin as the positive rail. This pin is charged to VSW + 6V when the Low-Side Power Switch turns on. Innovative Products. Active Solutions. -4- The COMP voltage is the integration of the error between the FB input and the internal 1.222V reference. If FB is lower than the reference voltage, COMP tends to go higher to increase current to the output. Current limit happens when COMP reaches its maximum clamp value of 2.55V. The Oscillator normally switches at 400kHz. However, if the FB voltage is less than 0.7V, then the switching frequency decreases until it reaches a minimum of 60kHz at VFB = 0.5V. Shutdown Control The ACT4072 has an enable input EN for turning the IC on or off. When EN is less than 0.7V, the IC is in 6A low current shutdown mode and the output is discharged through the Low-Side Power Switch. When EN is higher than 1.3V, the IC is in normal operation mode. EN is internally pulled up with a 2A current source and can be left unconnected for always-on operation. Thermal Shutdown The ACT4072 automatically turns off when its junction temperature exceeds 160C. www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4072 APPLICATIONS INFORMATION Output Voltage Setting Figure 1 shows the connections for setting the output voltage. Select the proper ratio of the two feedback resistors RFB1 and RFB2 based on the output voltage. Typically, use RFB2 10k and determine RFB1 from the output voltage: Input Capacitor The input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the converter. A low ESR capacitor is highly recommended. Since a large current flows in and out of this capacitor during switching, its ESR also affects efficiency. The input capacitance needs to be higher than 10F. The best choice is the ceramic type, however, low ESR tantalum or electrolytic types may also be used provided that the RMS ripple current rating is higher than 50% of the output current. The input capacitor should be placed close to the IN and G pins of the IC, with shortest possible traces. In the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1F ceramic capacitor is placed right next to the IC. V RFB1 RFB2 OUT - 1 1.222V Figure 1: Output Voltage Setting (1) Output Capacitor Inductor Selection The inductor maintains a continuous current to the output load. This inductor current has a ripple that is dependent on the inductance value: higher inductance reduces the peak-to-peak ripple current. The trade off for high inductance value is the increase in inductor core size and series resistance, and the reduction in current handling capability. In general, select an inductance value L based on ripple current requirement: The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is: RRIPPLE LOUTMAX K RIPPLE RESR VIN 2 28fSW LCOUT (3) L VOUT VIN - VOUT VIN fSW IOUTMAXK RIPPLE (2) where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR resistance of the output capacitor, fSW is the switching frequency, L is the inductor value, COUT is the output capacitance. In the case of ceramic output capacitors, RESR is very small and does not contribute to the ripple. Therefore, a lower capacitance value can be used for ceramic type, typically choose a capacitance of about 22F. In the case of tantalum or electrolytic type, the ripple is dominated by RESR multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low due to ESR, typically choose a capacitor with less than 50m ESR. where VIN is the input voltage, VOUT is the output voltage, fSW is the switching frequency, IOUTMAX is the maximum output current, and KRIPPLE is the ripple factor. Typically, choose KRIPPLE = 20% to 30% corresponding to the peak-to-peak ripple current being 20% to 30% of the maximum output current. With this inductor value (Table 1), the peak inductor current is IOUT x (1 + KRIPPLE / 2). Make sure that this peak inductor current is less that the 2.4A current limit. Finally, select the inductor core size so that it does not saturate at 2.4A. Table 1: Typical Inductor Values VOUT L Rectifier Diode Use a Schottky diode as the rectifier to conduct current when the High-Side Power Switch is off. The Schottky diode must have current rating higher than the maximum output current and the reverse voltage rating higher than the maximum input voltage. 1.5V 6.8H 1.8V 6.8H 2.5V 10H 3.3V 15H 5V 22H -5- Innovative Products. Active Solutions. www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4072 Stability compensation Figure 2: Stability Compensation STEP 2. Set the zero fZ1 at 1/4 of the cross over frequency. If RCOMP is less than 15k, the equation for CCOMP is: C COMP 1 . 8 10 5 R COMP (F) (10) If RCOMP is limited to 15k, then the actual cross over frequency is 3.4/(VOUTCOUT). Therefore: CCOMP 1.3 x10 5VOUTCOUT : CCOMP2 is needed only for high ESR output capacitors or PCB parasitics (F) (11) The feedback system of the IC is stabilized by the components at the COMP pin, as shown in Figure 2. The DC loop gain of the system is determined by the following equation: STEP 3. If the output capacitor's ESR is high enough to cause a zero at lower than 4 times the cross over frequency, an additional compensation capacitor CCOMP2 is required. The condition for using CCOMP2 is: AVDC 1.222V AVEAGCOMP IOUT (4) 1.1x10 6 ,0.012VOUT R ESROUT Min C OUT And the proper value for CCOMP2 is: () (12) The dominant pole P1 is due to CCOMP: fP 1 GEA 2 AVEA CCOMP CCOMP2 (5) COUT RESROUT RCOMP (13) The second pole P2 is the output pole: A small value CCOMP2 such as 100pF may improve stability against PCB layout parasitic effects. (6) Table 2 shows some calculated results based on the compensation method above. Table 2: (7) Typical Compensation for Different Output voltages and Output Capacitors VOUT 2.5V 3.3V fP 2 IOUT 2 VOUTCOUT 1 2 RCOMP CCOMP The first zero Z1 is due to RCOMP and CCOMP: fZ1 And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used): COUT 22F Ceramic 22F Ceramic 22F Ceramic 47F SP CAP 47F SP CAP 47F SP CAP 470F/6.3V/30m 470F/6.3V/30m 470F/6.3V/30m RCOMP CCOMP CCOMP2 8.2k 12k 15k 15k 15k 15k 15k 15k 15k 2.2nF 1.5nF 1.5nF 1.5nF 1.8nF 2.7nF 15nF 22nF 27nF 100pF 100pF 100pF 100pF 100pF 100pF 1nF 1nF 1nF fP 3 1 2 RCOMPCCOMP2 (8) 5V 2.5V 3.3V 5V 2.5V 3.3V 5V Follow the following steps to compensate the IC: STEP 1. Set the cross over frequency at 1/10 of the switching frequency via RCOMP: RCOMP 2 VOUT COUT fSW 10GEAGCOMP 1.222V 8 2.3 x10 VOUT COUT but limit RCOMP to 15k maximum. Innovative Products. Active Solutions. () (9) : CCOMP2 is needed for board parasitic and high ESR output capacitor. Figure 3 shows an example ACT4072 application circuit generating a 5V/2A output. -6www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4072 Figure 3: ACT4072 5V/2A Output Application Up to 30V VIN ENABLE IN BS SW IC1 ACT4072 FB EN G COMP C3 10nF L1 22H/3A R1 39.2k 5V/2A VOUT + C1 10F/35V C2 1.5nF R3 1.5k C5 100pF R2 12.1k D1 C4 22F/10V ceramic or 47H/6.3 SP Cap : D1 is a 40V, 3A Schottky diode with low forward voltage, an IR 30BQ040 or SK34 equivalent. C4 can be either a ceramic capacitor (Panasonic ECJ-3YB1C226M) or SP-CAP (Specialty Polymer) Aluminum Electrolytic Capacitor such as Panasonic EEFCD0J470XR. The SP-Cap is based on aluminum electrolytic capacitor technology, but uses a solid polymer electrolyte and has very stable capacitance characteristics in both operating temperature and frequency compared to ceramic, polymer, and low ESR tantalum capacitors. Innovative Products. Active Solutions. -7- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4072 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 3, unless otherwise specified.) Efficiency vs. Output Current 100 90 80 100 90 80 ACT4072-0001 Efficiency vs. Output Current ACT4072-0002 Efficiency (%) Efficiency (%) 70 60 50 40 30 20 10 0 0.01 0.1 VIN = 12V VIN = 25V VIN = 6V 70 60 50 40 30 20 10 VOUT = 5V L = 22H CIN = 10F COUT = 22F VIN = 30V VIN = 12V VIN = 8V VOUT = 3.3V L = 15H CIN = 10F COUT = 22F 1 10 0 0.01 0.1 1 10 Output Current (A) Output Current (A) Switching Frequency vs. Input Voltage Shutdown Supply Current (mA) 410 18 16 14 12 10 8 6 4 2 0 ACT4072-0003 Shutdown Supply Current vs. Input Voltage ACT4072-0004 Switching Frequency(kHz) 405 400 395 390 385 380 0.0 0.5 1.0 1.5 2.0 2.5 5 10 15 20 25 30 Temperature (C) Input Voltage (V) Surface Temperature vs. Output Current 80 1.27 ACT4072-0005 Feedback Voltage vs. Temperature ACT4072-006 VIN = 12V Surface Temperature (C) Feedback Voltage (V) 70 VIN = 30V 60 50 40 30 20 0.0 0.5 1.0 1.5 VOUT=5V VIN = 12V L=22H CIN=10F COUT=22F 1.25 1.23 1.21 1.19 1.17 2.0 -40 -20 0 20 40 60 80 100 120 Output Current (A) Temperature (C) Innovative Products. Active Solutions. -8- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4072 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 3, unless otherwise specified.) Load Transient Response ACT4072-0007 Load Transient Response ACT4072-0008 VOUT 200mV/div VOUT 200mV/div 2A IOUT 1A IOUT 0A VIN = 12V 1A VIN = 12V 100s/div 100s/div Innovative Products. Active Solutions. -9- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4072 PACKAGE OUTLINE SOP-8 PACKAGE OUTLINE AND DIMENSIONS SYMBOL A A1 A2 B C D E E1 e L DIMENSION IN MILLIMETERS MIN 1.350 0.100 1.350 0.330 0.190 4.780 3.800 5.800 DIMENSION IN INCHES MIN 0.053 0.004 0.053 0.013 0.007 0.188 0.150 0.228 MAX 1.750 0.250 1.550 0.510 0.250 5.000 4.000 6.300 MAX 0.069 0.010 0.061 0.020 0.010 0.197 0.157 0.248 1.270 TYP 0.400 0 1.270 8 0.050 TYP 0.016 0 0.050 8 Active-Semi, Inc. reserves the right to modify the circuitry or specifications without notice. Users should evaluate each product to make sure that it is suitable for their applications. Active-Semi products are not intended or authorized for use as critical components in life-support devices or systems. Active-Semi, Inc. does not assume any liability arising out of the use of any product or circuit described in this datasheet, nor does it convey any patent license. Active-Semi and its logo are trademarks of Active-Semi, Inc. For more information on this and other products, contact sales@active-semi.com or visit http://www.active-semi.com. For other inquiries, please send to: 1270 Oakmead Parkway, Suite 310, Sunnyvale, California 94085-4044, USA Innovative Products. Active Solutions. - 10 - www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. |
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