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| ACT4060 Rev8, 24-Jul-07 Wide Input 2A Step Down Converter FEATURES 2A Output Current Up to 95% Efficiency 4.75V to 20V Input Range 8A Shutdown Supply Current 420kHz 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 ACT4060 is a current-mode step-down DC/DC converter that generates up to 2A of output current at 420kHz switching frequency. The device utilizes Active-Semi's proprietary ISOBCD20 process for operation with input voltages up to 20V. Consuming only 8A in shutdown mode, the ACT4060 is highly efficient with peak operating efficiency at 95%. Protection features include cycle-bycycle current limit, thermal shutdown, and frequency foldback at short circuit. The ACT4060 is available in a SOP-8 package and requires very few external devices for operation. SOP-8 Package APPLICATIONS TFT LCD Monitors Portable DVDs Car-Powered or Battery-Powered Equipments Set-Top Boxes Telecom Power Supplies DSL and Cable Modems and Routers Termination Supplies TYPICAL APPLICATION CIRCUIT Innovative Products. Active Solutions. -1- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4060 Rev8, 24-Jul-07 ORDERING INFORMATION PART NUMBER ACT4060SH ACT4060SH-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 DESCRIPTIONS 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 capacitor between BS and SW. Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in the 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 1.293V. Connect to the resistor divider between output and ground to set output voltage. Compensation Pin. See Stability Compensation in the Application Information section. Enable Input. When higher than 1.3V, this pin turns the IC on. When lower than 0.7V, this pin turns the IC off. Output voltage is discharged when the IC is off. When left unconnected, EN is pulled up to 4.5V tip with a 2A pull-up current. Not Connected. 7 8 EN N/C Innovative Products. Active Solutions. -2- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4060 Rev8, 24-Jul-07 ABSOLUTE MAXIMUM RATINGS PARAMETER IN Supply Voltage SW Voltage BS Voltage EN, FB, COMP Voltage Continuous SW Current Junction to Ambient Thermal Resistance (JA) Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, 10 sec) VALUE -0.3 to 25 -1 to VIN + 1 VSW - 0.3 to VSW + 8 -0.3 to 6 Internally Limited 105 0.76 -40 to 150 -55 to 150 300 UNIT V V V V A C/W W 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 SYMBOL VIN VFB RONH RONL TEST CONDITIONS VOUT = 5V, ILOAD = 0A to 1A 4.75V VIN 20V, VCOMP = 1.5V MIN 7 1.267 TYP MAX 20 UNIT V V 1.293 0.20 4.7 1.319 VEN = 0 ILIM GCOMP GEA AVEA fSW VFB = 0 DMAX VFB = 1.1V VFB = 1.4V Hysteresis = 0.1V Pin pulled up to 4.5V typically when left unconnected VEN = 0 VEN = 3V, VFB = 1.4V Hysteresis = 10C 0.7 350 ICOMP = 10A 2.4 0 2.85 1.8 550 4000 420 50 90 10 A A A/V A/V V/V 490 kHz kHz % 0 1 2 8 0.7 160 20 1.3 % V A A mA C Innovative Products. Active Solutions. -3- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4060 Rev8, 24-Jul-07 FUNCTIONAL BLOCK DIAGRAM IN EN ENABLE REGULATOR & REFERENCE BS CURRENT SENSE AMPLIFIER COMP 1.293V + ERROR AMPLIFIER + + FB FOLDBACK CONTROL OSCILLATOR & RAMP - + - PWM COMP 0.2 HIGH-SIDE POWER SWITCH SW LOGIC THERMAL SHUTDOWN 4.7LOW-SIDE POWER SWITCH G FUNCTIONAL DESCRIPTION As seen in Functional Block Diagram, the ACT4060 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 the 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 output. This state continues until the cycle starts again. The High-Side Power Switch is driven by logic using BS as the positive rail. This pin is charged to VSW + 6V when the Low-Side Power Switch turns on. The COMP voltage is the integration of the error between FB input and the internal 1.293V 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 420kHz. However, if FB voltage is less than 0.7V, then the switching frequency decreases until it reaches a typical value of 50kHz at VFB = 0.5V. Shutdown Control The ACT4060 has an enable input EN for turning the IC on or off. When EN is less than 0.7V, the IC is in 8A low current shutdown mode and 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. Note that EN is a low voltage input with a maximum voltage of 6V, it should never be directly connected to IN. Thermal Shutdown The ACT4060 automatically turns off when its junction temperature exceeds 160C. -4www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. Innovative Products. Active Solutions. ACT4060 Rev8, 24-Jul-07 APPLICATIONS INFORMATION Output Voltage Setting Figure 1: Output Voltage Setting 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 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 the shortest traces possible. 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. VOUT ACT4060 FB RFB2 RFB1 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 following equation: Output Capacitor The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is: VRIPPLE IOUTMAX K RIPPLE RESR V R FB1 R FB 2 OUT 1 1.293V (1) 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: VIN 28 fSW LC OUT 2 (3) L VOUT VIN VOUT VIN fSW IOUTMAX K RIPPLE (2) 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 = 30% to correspond to the peak-to-peak ripple current being 30% of the maximum output current. With this inductor value, the peak inductor current is IOUT x (1 + KRIPPLE/2). Make sure that this peak inductor current is less that the 3A current limit. Finally, select the inductor core size so that it does not saturate at 3A. Typical inductor values for various output voltages are shown in Table 1. Table 1: Typical Inductor Values VOUT L where IOUTMAX is the maximum output current, KRIPPLE is the ripple factor, RESR is the ESR of the output capacitor, fSW is the switching frequency, L is the inductor value, and 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. In the case of tantalum or electrolytic capacitors, the ripple is dominated by RESR multiplied by the ripple current. In that case, the output capacitor is chosen to have sufficiently low ESR. For ceramic output capacitor, typically choose a capacitance of about 22F. For tantalum or electrolytic capacitors, choose a capacitor with less than 50m ESR. 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 a 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 Innovative Products. Active Solutions. -5- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4060 Rev8, 24-Jul-07 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 1.2 105 VOUTCOUT (F) (11) : CCOMP2 is needed only for high ESR output capacitor The feedback loop 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: 1.1 10 6 ,0.012 VOUT () RESRCOUT Min C OUT And the proper value for CCOMP2 is: (12) AVDC 1.3V AVEA GCOMP I OUT (4) The dominant pole P1 is due to CCOMP: G EA fP1 2 A VEA C COMP The second pole P2 is the output pole: fP 2 I OUT 2 V OUT C OUT CCOMP2 (5) COUT RESRCOUT RCOMP (13) Though CCOMP2 is unnecessary when the output capacitor has sufficiently low ESR, a small value CCOMP2 such as 100pF may improve stability against PCB layout parasitic effects. Table 2 shows some calculated results based on the compensation method above. Table 2: (6) The first zero Z1 is due to RCOMP and CCOMP: fZ1 1 2 R COMP C COMP2 (7) Typical Compensation for Different Output Voltages and Output Capacitors VOUT 2.5V 3.3V 5V 2.5V 3.3V 5V 2.5V 3.3V 5V And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used): fP 3 1 2 R COMP C COMP2 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 8.2k 12k 15k 15k 15k 15k 15k 15k 15k CCOMP CCOMP2 2.2nF 1.5nF 1.5nF 1.5nF 1.8nF 2.7nF 15nF 22nF 27nF None None None None None None 1nF 1nF None (8) The following steps should be used to compensate the IC: STEP 1. Set the cross over frequency at 1/10 of the switching frequency via RCOMP: R COMP 2 VOUT C OUT fSW 10 G EA G COMP 1.3V 8 : CCOMP2 is needed for high ESR output capacitor. 1.7 10 VOUT C OUT () (9) Figure 3 shows an example ACT4060 application circuit generating a 2.5V/2A output. but limit RCOMP to 15k maximum. Innovative Products. Active Solutions. -6- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4060 Rev8, 24-Jul-07 Figure 3: ACT4060 2.5V/2A Output Application : 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. ACT4060 Rev8, 24-Jul-07 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 3, unless otherwise specified.) Feedback Voltage vs. Junction Temperature 1.33 450 Switching Frequency vs. Input Voltage ACT4060-002 Switching Frequency (kHz) ACT4060-001 Feedback Voltage (V) 1.31 430 1.29 410 1.27 390 1.25 -40 0 40 80 120 370 5 10 15 20 Junction Temperature (C) Input Voltage (V) Efficiency vs. Output Current ACT4060-003 95 93 Efficiency (%) 90 88 VIN = 7V VOUT = 5V 85 0.1 0.5 0.9 1.3 1.7 Output Current (A) Innovative Products. Active Solutions. -8- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. ACT4060 Rev8, 24-Jul-07 PACKAGE OUTLINE SOP-8 PACKAGE OUTLINE AND DIMENSIONS C D SYMBOL A A1 A2 B C e B DIMENSION IN MILLIMETERS MIN 1.350 0.100 1.350 0.330 0.190 4.700 3.800 5.800 DIMENSION IN INCHES MIN 0.053 0.004 0.053 0.013 0.007 0.185 0.150 0.228 MAX 1.750 0.250 1.550 0.510 0.250 5.100 4.000 6.300 MAX 0.069 0.010 0.061 0.020 0.010 0.201 0.157 0.248 D E E1 e L 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. -9- www.active-semi.com Copyright (c) 2006 Active-Semi, Inc. |
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