ACT4060

Innovative Products. Active Solutions. - 1 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. FEATURES  2A Output Current  Up to 95% Efficiency  4.75V to 20V Input Range  8µA 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  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 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 8μA in shutdown mode, the ACT4060 is highly efficient with peak operating effi- ciency at 95%. Protection features include cycle-by- cycle 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. TYPICAL APPLICATION CIRCUIT ACT4060 Rev8, 24-Jul-07 Wide Input 2A Step Down Converter ACT4060 Innovative Products. Active Solutions. - 2 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev8, 24-Jul-07 ORDERING INFORMATION PART NUMBER TEMPERATURE RANGE PACKAGE PINS PACKING ACT4060SH -40°C to 85°C SOP-8 8 TUBE ACT4060SH-T -40°C to 85°C SOP-8 8 TAPE & REEL PIN CONFIGURATION PIN DESCRIPTIONS PIN NUMBER PIN NAME PIN DESCRIPTION 1 BS Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver. Connect a 10nF capacitor between BS and SW. 2 IN Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in the Application Information section. 3 SW Switch Output. Connect this pin to the switching end of the inductor. 4 G Ground. 5 FB 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. 6 COMP Compensation Pin. See Stability Compensation in the Application Information section. 7 EN 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 2µA pull-up current. 8 N/C Not Connected. SOP-8 ACT4060 Innovative Products. Active Solutions. - 3 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev8, 24-Jul-07 ABSOLUTE MAXIMUM RATINGS PARAMETER VALUE UNIT IN Supply Voltage -0.3 to 25 V SW Voltage -1 to VIN + 1 V BS Voltage VSW - 0.3 to VSW + 8 V EN, FB, COMP Voltage -0.3 to 6 V Continuous SW Current Internally Limited A Junction to Ambient Thermal Resistance (θJA) 105 °C/W Maximum Power Dissipation 0.76 W Operating Junction Temperature -40 to 150 °C Storage Temperature -55 to 150 °C Lead Temperature (Soldering, 10 sec) 300 °C ELECTRICAL CHARACTERISTICS (VIN = 12V, TA = 25°C, unless otherwise specified.) PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT Input Voltage VIN VOUT = 5V, ILOAD = 0A to 1A 7 20 V Feedback Voltage VFB 4.75V ≤ VIN ≤ 20V, VCOMP = 1.5V 1.267 1.293 1.319 V High-Side Switch On Resistance RONH 0.20 Ω Low-Side Switch On Resistance RONL 4.7 Ω SW Leakage VEN = 0 0 10 µA Current Limit ILIM 2.4 2.85 A COMP to Current Limit Transconductance GCOMP 1.8 A/V Error Amplifier Transconductance GEA ΔICOMP = ±10µA 550 µA/V Error Amplifier DC Gain AVEA 4000 V/V Switching Frequency fSW 350 420 490 kHz Short Circuit Switching Frequency VFB = 0 50 kHz Maximum Duty Cycle DMAX VFB = 1.1V 90 % Minimum Duty Cycle VFB = 1.4V 0 % Enable Threshold Voltage Hysteresis = 0.1V 0.7 1 1.3 V Enable Pull-Up Current Pin pulled up to 4.5V typically when left unconnected 2 µA Supply Current in Shutdown VEN = 0 8 20 µA IC Supply Current in Operation VEN = 3V, VFB = 1.4V 0.7 mA Thermal Shutdown Temperature Hysteresis = 10°C 160 °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. ACT4060 Innovative Products. Active Solutions. - 4 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev8, 24-Jul-07 FUNCTIONAL BLOCK DIAGRAM 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 con- nected 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 re- sulting 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 volt- age 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 refer- ence. 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. How- ever, 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 8μA 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 2μA 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 junc- tion temperature exceeds 160°C. IN EN COMP FB BS SW LOGIC THERMAL SHUTDOWN REGULATOR & REFERENCE + - OSCILLATOR & RAMP FOLDBACK CONTROL 1.293V ERROR AMPLIFIER ENABLE 0.2Ω HIGH-SIDE POWER SWITCH G + - + - - + PWM COMP CURRENT SENSE AMPLIFIER 4.7Ω LOW-SIDE POWER SWITCH ACT4060 Innovative Products. Active Solutions. - 5 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev8, 24-Jul-07 Figure 1 shows the connections for setting the out- put voltage. Select the proper ratio of the two feed- back resistors RFB1 and RFB2 based on the output voltage. Typically, use RFB2 ≈ 10kΩ and determine RFB1 from the following equation: The inductor maintains a continuous current to the output load. This inductor current has a ripple that is dependent on the inductance value: higher induc- tance 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: VOUT 1.5V 1.8V 2.5V 3.3V 5V L 6.8μH 6.8μH 10μH 15μH 22μH where IOUTMAX is the maximum output current, KRIP- PLE 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 electro- lytic 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 22µF. For tantalum or electro- lytic capacitors, choose a capacitor with less than 50mΩ ESR. Rectifier Diode Use a Schottky diode as the rectifier to conduct cur- rent 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. Inductor Selection APPLICATIONS INFORMATION 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 rip- ple factor. Typically, choose KRIPPLE = 30% to corre- spond to the peak-to-peak ripple current being 30% of the maximum output current. With this inductor value, the peak inductor current is IOUT × (1 + KRIPPLE/2). Make sure that this peak in- ductor current is less that the 3A current limit. Fi- nally, select the inductor core size so that it does not saturate at 3A. Typical inductor values for vari- ous output voltages are shown in Table 1. (1) (2) Figure 1: Output Voltage Setting     1 V293.1 V RR OUT2FB1FB   RIPPLEOUTMAXSWIN OUTINOUT KIfV VVV L  (3) ESRRIPPLEOUTMAXRIPPLE RKIV  OUT 2 SW IN LCf28 V  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 rec- ommended. 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 10µF. The best choice is the ceramic type, how- ever, 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 0.1µF ce- ramic capacitor is placed right next to the IC. Output Capacitor The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is: Output Voltage Setting RFB1 RFB2 VOUT ACT4060 FB Table 1: Typical Inductor Values ACT4060 Innovative Products. Active Solutions. - 6 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev8, 24-Jul-07 STABILITY COMPENSATION STEP 2. Set the zero fZ1 at 1/4 of the cross over frequency. If RCOMP is less than 15kΩ, the equation for CCOMP is: If RCOMP is limited to 15kΩ, then the actual cross over frequency is 3.4 / (VOUTCOUT). Therefore: 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: And the proper value for CCOMP2 is: Though CCOMP2 is unnecessary when the output ca- pacitor 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: Typical Compensation for Different Output Voltages and Output Capacitors VOUT COUT RCOMP CCOMP CCOMP2 2.5V 22μF Ceramic 8.2kΩ 2.2nF None 3.3V 22μF Ceramic 12kΩ 1.5nF None 5V 22μF Ceramic 15kΩ 1.5nF None 2.5V 47μF SP CAP 15kΩ 1.5nF None 3.3V 47μF SP CAP 15kΩ 1.8nF None 5V 47μF SP CAP 15kΩ 2.7nF None 2.5V 470μF/6.3V/30mΩ 15kΩ 15nF 1nF 3.3V 470μF/6.3V/30mΩ 15kΩ 22nF 1nF 5V 470μF/6.3V/30mΩ 15kΩ 27nF None : CCOMP2 is needed for high ESR output capacitor. Figure 3 shows an example ACT4060 application circuit generat- ing a 2.5V/2A output. COMP ESRCOUTOUT 2COMP R RCC  (13) Figure 2: Stability Compensation (10) (F) COMP 5 COMP R 108.1C  (11) (F) OUTOUT 5 COMP CV102.1C  : 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: The dominant pole P1 is due to CCOMP: And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used): 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: but limit RCOMP to 15kΩ maximum. The first zero Z1 is due to RCOMP and CCOMP: The second pole P2 is the output pole: COMP2COMP 3P CRπ2 1f  (8) (Ω) (9) V3.1GG10 fCVπ2R COMPEA SWOUTOUT COMP  OUTOUT 8 CV107.1  (4) COMPVEA OUT VDC GAI V3.1A  (5) COMPVEA EA 1P CAπ2 Gf  (6) OUTOUT OUT 2P CVπ2 If  (12) (Ω)       OUT OUT 6 ESRCOUT V012.0,C 101.1MinR (7) COMP2COMP 1Z CRπ2 1f  ACT4060 Innovative Products. Active Solutions. - 7 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. 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 capaci- tance characteristics in both operating temperature and frequency compared to ceramic, polymer, and low ESR tantalum capacitors. ACT4060 Innovative Products. Active Solutions. - 8 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev8, 24-Jul-07 TYPICAL PERFORMANCE CHARACTERISTICS Input Voltage (V) 5 10 15 20 AC T4060-002 Switching Frequency vs. Input Voltage 390 410 370 S w itc hi ng F re qu en cy (k H z) 430 450 -40 Junction Temperature (°C) 0 40 80 120 AC T4060-001 1.29 1.33 1.31 1.27 1.25 Fe ed ba ck V ol ta ge (V ) Feedback Voltage vs. Junction Temperature (Circuit of Figure 3, unless otherwise specified.) Output Current (A) 93 E ffi ci en cy (% ) AC T4060-003 0.1 0.5 0.9 1.3 Efficiency vs. Output Current 1.7 VIN = 7V VOUT = 5V 95 90 88 85 ACT4060 Innovative Products. Active Solutions. - 9 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev8, 24-Jul-07 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 PACKAGE OUTLINE SOP-8 PACKAGE OUTLINE AND DIMENSIONS SYMBOL DIMENSION IN MILLIMETERS DIMENSION IN INCHES MIN MAX MIN MAX A 1.350 1.750 0.053 0.069 A1 0.100 0.250 0.004 0.010 A2 1.350 1.550 0.053 0.061 B 0.330 0.510 0.013 0.020 C 0.190 0.250 0.007 0.010 D 4.700 5.100 0.185 0.201 E 3.800 4.000 0.150 0.157 E1 5.800 6.300 0.228 0.248 e 1.270 TYP 0.050 TYP L 0.400 1.270 0.016 0.050 θ 0° 8° 0° 8° θ C D B e