ACT4070 Rev 0, 12/2006 Wide Input 3A Step Down Converter FEATURES GENERAL DESCRIPTION 3A Output Current The ACT4070 is a current-mode step-down DC/DC converter that generates up to 3A output current at 400kHz switching frequency. The device utilizes Active-Semi’s proprietary ISOBCD30 process for operation with input voltage up to 30V. Up to 95% Efficiency 4.5V to 30V Input Range 6µA Shutdown Supply Current 400kHz Switching Frequency Consuming only 6μA in shutdown mode, the ACT4070 is highly efficient with peak efficiency at 95% when in operation. Protection features include cycle-by-cycle current limit, thermal shutdown, and frequency fold back at short circuit. The device also includes an internal soft start function to prevent overshoot. Adjustable Output Voltage Cycle-by-Cycle Current Limit Protection Thermal Shutdown Protection Internal Soft Start Function Frequency Fold Back at Short Circuit The ACT4070 is available in SOP-8/EP exposed pad package and requires very few external devices for operation. Stability with Wide Range of Capacitors, Including Low ESR Ceramic Capacitors SOP-8/EP (Exposed Pad) 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. Copyright © 2006 Active-Semi, Inc. -1- www.active-semi.com ACT4070 ORDERING INFORMATION PART NUMBER TEMPERATURE RANGE PACKAGE PINS PACKING ACT4070YH -40°C to 85°C SOP-8/EP 8 TUBE ACT4070YH-T -40°C to 85°C SOP-8/EP 8 TAPE & REEL PIN CONFIGURATION SOP-8/EP PIN DESCRIPTION PIN NUMBER PIN NAME 1 BS Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver. Connect a 10nF between this pin and SW. 2 IN Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in Application Information section. 3 SW 4 G Ground. 5 FB Feedback Input. The voltage at this pin is regulated to 1.222V. Connect to the resistor divider between output and ground to set output voltage. 6 COMP Compensation Pin. See Compensation Technique in 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. This pin has a small internal pull up current to a high level voltage when pin is not connected. 8 N/C Not Connected. EP Exposed Pad shown as dashed box. The exposed thermal pad should be connected to board ground plane and pin 4. The ground plane should include a large exposed copper pad under the package for thermal dissipation (see package outline). The leads and exposed pad should be flush with the board, without offset from the board surface. EP PIN DESCRIPTION Switch Output. Connect this pin to the switching end of the inductor. Innovative Products. Active Solutions. Copyright © 2006 Active-Semi, Inc. -2- www.active-semi.com ACT4070 ABSOLUTE MAXIMUM RATINGS PARAMETER VALUE UNIT IN to G -0.3 to +34 V EN to G -0.3 to VIN + 0.3 V SW to G -1 to VIN + 1 V BS to SW -0.3 to +8 V FB, COMP to G -0.3 to 6 V Internally limited A Junction to Ambient Thermal Resistance (θJA) 46 °C/W Maximum Power Dissipation 1.8 W Operating Junction Temperature -40 to 150 °C Storage Temperature -55 to 150 °C 300 °C Continuous SW Current Lead Temperature (Soldering, 10 sec) : 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= 25°C, unless otherwise specified.) PARAMETER SYMBOL TEST CONDITIONS MIN VIN Feedback Voltage VFB 1.198 1.222 1.246 V High-Side Switch On Resistance RONH 100 mΩ Low-Side Switch On Resistance RONL 10 Ω Current Limit VEN = 0, VIN = 12V, VSW = 0V GCOMP Error Amplifier Transconductance GEA Error Amplifier DC Gain AVEA 3.5 ΔILOAD/ΔICOMP ΔICOMP = ±10µA fSW Short Circuit Switching Frequency 30 0 ILIM COMP to Current Limit Transconductance Switching Frequency 4.5 MAX UNIT Input Voltage SW Leakage VOUT = 2.5V, ILOAD = 0A to 3A TYP 340 10 V µA 5 A 3 A/V 550 µA/V 4000 V/V 400 460 kHz VFB = 0V 40 kHz VFB = 1.1V, PWM mode 90 % Minimum Duty Cycle VFB = 1.4V, PFM mode 0 % Enable Threshold Voltage Hysteresis = 0.1V Enable Pull Up Current Pin pulled up to VIN when left unconnected 2 Supply Current in Shutdown VEN = 0 6 20 µA IC Supply Current in Operation VEN = 3V, not switching 0.85 2 mA Thermal Shutdown Temperature Hysteresis = 10°C 160 Maximum Duty Cycle DMAX Innovative Products. Active Solutions. 0.7 1 1.3 V µA °C Copyright © 2006 Active-Semi, Inc. -3- www.active-semi.com ACT4070 FUNCTIONAL BLOCK DIAGRAM FUNCTIONAL DESCRIPTION As seen in the Functional Block Diagram, the ACT4070 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 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 output. This state continues until the cycle starts again. The High-Side Power Switch is driven by logic using 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. The COMP voltage is the integration of the error between 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 2.65V. The Oscillator normally switches at 400kHz. However, if FB voltage is less than 0.7V, then the switching frequency decreases until it reaches a typical value of 40kHz at VFB = 0V. Shutdown Control The ACT4070 has an enable input EN for turning the IC on or off. When EN is less than 0.7V, the IC is in 6μA 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. Thermal Shutdown The ACT4070 automatically turns off when its junction temperature exceeds 160°C and then restarts once the temperature falls to 150°C. Copyright © 2006 Active-Semi, Inc. -4- www.active-semi.com ACT4070 APPLICATIONS INFORMATION Output Voltage Setting Input Capacitor 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 ≈ 10kΩ and determine RFB1 from the output voltage: 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. V RFB1 RFB2 OUT - 1 1.222V (1) The input capacitance needs to be higher than 10µF. 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 traces possible. In the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1µF ceramic capacitor is placed right next to the IC. Figure 1: Output Voltage Setting Output Capacitor The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is: 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: L VOUT VIN - VOUT VIN fSW IOUTMAX K RIPPLE VRIPPLE IOUTMAX K RIPPLE RRIPPLE 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 = between 20% and 30% to correspond to the peak-to-peak ripple current being a percentage of the maximum output current. 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. Typical Inductor Values 2.5V 3.3V 5V L 6.8μH 6.8μH 6.8μH 8.5μH 15μH (3) Rectifier Diode Table 1: 1.8V 2 For ceramic output type, typically choose a capacitance of about 22µF. For tantalum or electrolytic type, choose a capacitor with less than 50mΩ ESR. With this inductor value (Table 1), the peak inductor current is IOUT (1 + KRIPPLE / 2). Make sure that this peak inductor current is less that the 5A current limit. Finally, select the inductor core size so that it does not saturate at 5A. 1.5V 28 fSW LCOUT 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 in 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. 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 ESR. (2) VOUT VIN Innovative Products. Active Solutions. Copyright © 2006 Active-Semi, Inc. -5- www.active-semi.com ACT4070 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: Figure 2: Stability Compensation CCOMP 1.6 x10 5 RCOMP (10) (F) If RCOMP is limited to 15kΩ, then the actual cross over frequency is 4.8/(VOUTCOUT). Therefore: CCOMP 8.8 x10 6 VOUT COUT The feedback system of the IC is stabilized by the components at COMP pin, as shown in Figure 2. The DC loop gain of the system is determined by the following equation: 1.222V AVEAGCOMP IOUT RESROUT 1.1x10 6 Min ,0.012VOUT COUT (4) The dominant pole P1 is due to CCOMP: fP 1 G EA 2 A VEA C COMP CCOMP (5) IOUT 2 VOUT C OUT (6) 1 COUT R ESROUT RCOMP (13) Table 2 shows some calculated results based on the compensation method above. (7) 2 RCOMP CCOMP (12) Though CCOMP2 is unnecessary when the output capacitor has sufficiently low ESR, a small value CCOMP2 such as 220pF may improve stability against PCB layout parasitic effects. The first zero Z1 is due to RCOMP and CCOMP: fZ1 (Ω) And the proper value for CCOMP2 is: The second pole P2 is the output pole: fP 2 (11) 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: : CCOMP2 is needed only for high ESR output capacitor AVDC (F) Table 2: Typical Compensation for Different Output Voltages and Output Capacitors And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used): CCOMP CCOMP2 VOUT COUT RCOMP 1.8V 22μF Ceramic 4kΩ 3.3nF 220pF 2.5V 22μF Ceramic 5.6kΩ 3.3nF 220pF Follow the following steps to compensate the IC: 5V 22μF Ceramic 12kΩ 1.5nF 220pF STEP 1. Set the cross over frequency at 1/10 of the switching frequency via RCOMP: 1.8V 100μF SP CAP 15kΩ 1.5nF 220pF 2.5V 100μF SP CAP 15kΩ 2.2nF 220pF 5V 100μF SP CAP 15kΩ 4.7nF 220pF fP 3 1 (8) 2 RCOMP CCOMP2 RCOMP 2 VOUT COUT fSW 10 GEAGCOMP 1 .222 V 1 .25 x10 8 VOUT COUT (Ω) : CCOMP2 is needed for board parasitic and high ESR output capacitor. (9) Figure 3 shows a sample ACT4070 application circuit generating a 2.5V/3A output. but limit RCOMP to 15kΩ maximum. Innovative Products. Active Solutions. Copyright © 2006 Active-Semi, Inc. -6- www.active-semi.com ACT4070 Figure 3: ACT4070 2.5V/3A Output Application C3 10nF BS 4.5V to 30V VIN IN IC1 ACT4070 EN ENABLE G + C1 10µF/35V L1 10µH/4A SW 2.5V/3A VOUT R1 14k FB COMP C2 (CCOMP) 3.3nF R3 (RCOMP) 5.6k C5 (CCOMP2) 220pF R2 13k D1 40V 3A C4 (COUT) 22µF/10V ceramic or 47µH/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. Copyright © 2006 Active-Semi, Inc. -7- www.active-semi.com ACT4070 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 3, unless otherwise specified.) Efficiency vs. Output Current Efficiency vs. Output Current Efficiency (%) 70 60 90 VIN = 12V 50 VIN = 30V 40 VIN = 20V 30 20 0 0.01 0.1 1 70 60 VIN = 30V 50 VIN = 12V 40 30 VIN = 20V VOUT = 2.5V L = 10µH CIN = 22µF COUT = 22µF 20 VOUT = 5V L = 15µH CIN = 22µF COUT = 22µF 10 VIN = 8V 80 Efficiency (%) VIN = 8V 80 ACT4070-0002 90 100 ACT4070-0001 100 10 0 0.01 10 0.1 Output Current (A) Feedback Voltage vs. Temperature Switching Frequency vs. Input Voltage 1.23 Switching Frequency (kHz) 1.25 1.21 1.19 1.17 ACT4070-0004 Feedback Voltage (V) 10 500 ACT4070-0003 1.27 450 400 350 300 -40 -20 0 20 40 60 80 8 100 10 12 Temperature (°C) 14 16 18 20 22 24 26 28 30 Input Voltage (V) Surface Temperature vs. Output Current Shutdown Supply Current vs. Input Voltage 14 12 Surface Temperature (°C) 16 10 8 6 4 2 VOUT = 5V L = 15µH CIN = 22µF COUT = 22µF 120 VIN = 30V 100 80 ACT4070-006 140 ACT4070-0005 18 Shutdown Supply Current (µA) 1 Output Current (A) VIN = 20V 60 40 VIN = 12V 20 0 0 5 10 15 20 25 0 30 0.5 1 1.5 2 2.5 3 Output Current (A) Input Voltage (V) Innovative Products. Active Solutions. Copyright © 2006 Active-Semi, Inc. -8- www.active-semi.com ACT4070 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 3, unless otherwise specified.) Load Transient Response Load Transient Response ACT4070-0008 ACT4070-0007 VOUT 200mV/div VOUT 200mV/div 1A 1A IOUT IOUT 0A 0A VIN = 12V VIN = 12V 100µs/div 100µs/div Load Transient Response ACT4070-0009 VOUT 200mV/div 3A IOUT 2A VIN = 12V 100µs/div Innovative Products. Active Solutions. Copyright © 2006 Active-Semi, Inc. -9- www.active-semi.com ACT4070 PACKAGE OUTLINE SOP-8/EP PACKAGE OUTLINE AND DIMENSIONS DIMENSION IN MILLIMETERS DIMENSION IN INCHES MIN MAX MIN MAX A 1.350 1.750 0.053 0.069 A1 0.050 0.150 0.002 0.006 A2 1.350 1.550 0.053 0.061 b 0.330 0.510 0.013 0.020 c 0.170 0.250 0.007 0.010 D 4.700 5.100 0.185 0.200 D1 3.202 3.402 0.126 0.134 E 3.800 4.000 0.150 0.157 E1 5.800 6.200 0.228 0.244 E2 2.313 2.513 0.091 0.099 D b e D1 SYMBOL e 1.270 TYP 0.050 TYP L 0.400 1.270 0.016 0.050 θ 0° 8° 0° 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 [email protected] 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. Copyright © 2006 Active-Semi, Inc. - 10 - www.active-semi.com