ACT4065A ® Rev 0, 23-Apr-12 High Input 2A Step Down Converter FEATURES GENERAL DESCRIPTION • • • • • • • • • The ACT4065A is a current-mode step-down DC/DC converter that generates up to 2A output current at 210kHz switching frequency. 2A Output Current Up to 95% Efficiency 6.0V to 30V Input Range The ACT4065A 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. 210kHz Switching Frequency Adjustable Output Voltage Cycle-by-Cycle Current Limit Protection The ACT4065A is available in SOP-8 package and requires very few external devices for operation. Thermal Shutdown Protection Frequency Foldback at Short Circuit Stability with Wide Range of Capacitors, Including Low ESR Ceramic Capacitors Note: ACT4065A is the drop-in replacement for ACT4065 with feedback resistance value change. • 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 Efficiency vs. Load current ACT4065A-001 95 VIN = 12V Efficiency (%) 90 85 VIN = 24V 80 75 VOUT = 5V 70 10 100 1000 10000 Load Current (mA) Innovative PowerTM -1- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4065A ® Rev 0, 23-Apr-12 ORDERING INFORMATION PART NUMBER TEMPERATURE RANGE PACKAGE PINS PACKING ACT4065ASH-T -40°C to 85°C SOP-8 8 TAPE & REEL PIN CONFIGURATION SOP-8 PIN DESCRIPTION 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 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 0.808V. Connect to the resistor divider between output and ground to set output voltage. 6 COMP Compensation Pin. See Compensation Techniques in Application Information section. 7 EN Enable Input. When higher than 0.8V, this pin turns the IC on. When lower than 0.8V, this pin turn 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. Do not allow EN pin to exceed 6V. 8 N/C Not Connected. Innovative PowerTM Switch Output. Connect this pin to the switching end of the inductor. -2- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4065A ® Rev 0, 23-Apr-12 ABSOLUTE MAXIMUM RATINGSc PARAMETER VALUE UNIT -0.3 to 30 V SW Voltage -1 to VIN + 1 V BS Voltage VSW - 0.3 to VSW + 7 V EN, FB, COMP Voltage -0.3 to 6 V Continuous SW Current Internally limited A Maximum Power Dissipation 0.76 W Junction to Ambient Thermal Resistance (θJA ) 105 °C/W Operating Junction Temperature -40 to 150 °C Storage Temperature -55 to 150 °C 300 °C IN Supply Voltage Lead Temperature (Soldering, 10 sec) 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, TJ = 25˚C, unless otherwise specified.) PARAMETER SYMBOL TEST CONDITIONS Input Voltage VIN VOUT = 5V, ILOAD = 1A Feedback Voltage VFB VCOMP = 1.5V MIN TYP 6 0.792 0.808 MAX UNIT 30 V 0.824 V High-Side Switch On Resistance RONH 0.22 Ω Low-Side Switch On Resistance RONL 8 Ω SW Leakage High-Side Switch Current Limit VEN = 0 ILIM COMP to Current Limit Transconductance GCOMP Error Amplifier Transconductance GEA Error Amplifier DC Gain AVEA Switching Frequency Maximum Duty Cycle Duty = 50% ΔICOMP = ±10µA fSW Short Circuit Switching Frequency DMAX 1 190 10 µA 3.5 A 3.4 A/V 650 µA/V 4000 V/V 210 240 kHz VFB = 0 30 kHz VFB = 0.7V 88 % Minimum Duty Cycle VFB = 1.0V Enable Threshold Voltage Hysteresis = 0.1V Enable Pull-Up Current Pin pulled up to 4.5V typically when left unconnected 4 Supply Current in Shutdown VEN = 0 75 IC Supply Current in Operation VEN = 3V, VFB = 1.0V 0.75 mA Thermal Shutdown Temperature Hysteresis = 10°C 155 °C Innovative PowerTM -3- 0.75 0.8 0 % 0.85 V µA 100 µA www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4065A ® Rev 0, 23-Apr-12 FUNCTIONAL BLOCK DIAGRAM is charged to VSW + 5V when the Low-Side Power Switch turns on. FUNCTIONAL DESCRIPTION As seen in, Functional Block Diagram, the ACT4065A is a current mode pulse width modulation (PWM) converter. The converter operates as follows: The COMP voltage is the integration of the error between the FB input and the internal 0.808V 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 2.0V. 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 Oscillator normally switches at 210kHz. However, if the FB voltage is less than 0.6V, then the switching frequency decreases until it reaches a minimum of 30kHz at VFB = 0.15V. Shutdown Control The ACT4065A 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 . When EN is higher than 0.8V, the IC is in normal operation mode. EN is internally pulled up with a 4μA current source and can be left unconnected for always-on operation. EN should never be directly connected to IN. Thermal Shutdown The High-Side Power Switch is driven by logic using the BS bootstrap pin as the positive rail. This pin Innovative PowerTM The ACT4065A automatically turns off when its junction temperature exceeds 155°C. -4- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4065A ® Rev 0, 23-Apr-12 APPLICATIONS INFORMATION 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. Output Voltage Setting Figure 1: 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 ≈ 10kΩ and determine RFB1 from the output voltage: 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 possible traces. 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. Output Capacitor RFB1 ⎛ V ⎞ = RFB 2 ⎜ OUT − 1 ⎟ ⎝ 0.808V ⎠ The output capacitor also needs to have low ESR to keep low output voltage ripple. The output ripple voltage is: (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: 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 (Table 1), the peak inductor current is IOUT × (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. ⎛ VIN VRIPPLE = IOUTMAXK RIPPLERESR + ⎜⎜ 2 ⎝ 28 × fSW LCOUT ⎞ ⎟ (3) ⎟ ⎠ 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, 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. For ceramic output type, typically choose a capacitance of about 22µF. For tantalum or electrolytic type, choose a capacitor with less than 50mΩ ESR. Rectifier Diode Use a Schotky 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. Table 1. Typical Inductor Values VOUT 1.5V 1.8V 2.5V 3.3V 5V L 10μH 10μH 15μH 22μH 33μH Innovative PowerTM -5- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4065A ® Rev 0, 23-Apr-12 frequency. If RCOMP is less than 15kΩ, the equation for CCOMP is: Stability compensation Figure 2: Stability Compensation = C COMP −5 1 . 8 × 10 R COMP (10) (F) If RCOMP is limited to 15kΩ, then the actual cross over frequency is 6.1/ (VOUTCOUT). Therefore: C COMP = 1 . 2 × 10 5 V OUT C OUT 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: A VDC (4) ⎞ ⎛ 1.1 × 10 −6 RESROUT ≥ Min⎜⎜ ,0.012VOUT ⎟⎟ ⎠ ⎝ COUT fP1 CCOMP 2 = (5) I OUT 2 π VOUT C OUT 1 Typical Compensation for Different Output voltages and Output Capacitors And finally, the third pole is due to RCOMP and CCOMP2 (if CCOMP2 is used): fP 3 = 1 (8) 2π R COMP C COMP2 Follow the following steps to compensate the IC: STEP 1. Set the cross over frequency at 1/5 of the switching frequency via RCOMP: R COMP = 2 π V OUT C OUT f SW 10 G EA G COMP × 0 . 808 V = 2 . 75 × 10 8 V OUT C OUT (Ω) (9) CCOMP2c VOUT COUT 2.5V 22μF Ceramic 12kΩ 2.2nF None 3.3V 22μF Ceramic 12kΩ 1.5nF None 5V 22μF Ceramic 15kΩ 2.2nF 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 1.5nF 47pF 3.3V 470µF/6.3V/30mΩ 15kΩ 2.2nF 47pF 5V 470µF/10V/30mΩ 15kΩ 2.7nF 47pF RCOMP CCOMP c: CCOMP2 is needed only for high ESR output capacitors but limit RCOMP to 15kΩ maximum. Figure 3 shows a sample ACT4065A application circuit generating a 2.5V/2A output. STEP 2. Set the zero fZ1 at 1/4 of the cross over Innovative PowerTM (13) Table 2: (7) 2π RCOMP CCOMP COUT R ESROUT RCOMP Table 2 shows some calculated results based on the compensation method above. (6) The first zero Z1 is due to RCOMP and CCOMP: f Z1 = (12) 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. The second pole P2 is the output pole: fP 2 = (Ω) And the proper value for CCOMP2 is: The dominant pole P1 is due to CCOMP: G EA = 2 π AVEA C COMP (11) STEP 3. If the output capacitors 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 required. The condition for using CCOMP2 is: c: CCOMP2 is needed only for high ESR output capacitors 0 . 808 V = A VEA G COMP I OUT (F) -6- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4065A ® Rev 0, 23-Apr-12 Figure 3: Typical Application Circuit for 5V/2A Car Charger Table 3: BOM List for 5V/2A Car Charger ITEM REFERENCE 1 U1 IC, ACT4065ASH, SOP-8EP Active-Semi 1 2 C1 Capacitor, Electrolytic, 47µF/35V, 6.3х7mm Murata, TDK 1 3 C2 Capacitor, Ceramic, 10µF/35V, 1210, SMD Murata, TDK 1 4 C3 Capacitor, Ceramic, 2.2nF/6.3V, 0603, SMD Murata, TDK 1 5 C4 Capacitor, Ceramic, 10nF/50V, 0603, SMD Murata, TDK 1 6 C5 Capacitor, Electrolytic, 100µF/10V, 6.3х7mm Murata, TDK 1 7 C6 Capacitor, Ceramic, 1µF/10V, 0603, SMD Murata, TDK 1 8 L1 Inductor,33µH, 3.0A Sumida 1 9 D1 Diode, Schottky, 40V/2A, SB240 Diodes 1 10 R1 Chip Resistor, 52kΩ, 0603, 1% Murata, TDK 1 11 R3 Chip Resistor, 8.2kΩ, 0603, 5% Murata, TDK 1 12 R2 Chip Resistor, 10kΩ, 0603, 1% Murata, TDK 1 Innovative PowerTM DESCRIPTION -7- MANUFACTURER QTY www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4065A ® Rev 0, 23-Apr-12 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 3, unless otherwise specified .) Switching Frequency vs. Feedback Voltage Switching Frequency vs. Input Voltage 210 Switching Frequency (kHz) Switching Frequency (kHz) 230 190 170 150 130 ACT4065A-003 260 ACT4065A-002 250 210 160 110 60 10 110 6 8 10 15 20 25 0 30 100 200 Maximum Peak Current vs. Duty Cycle 400 500 600 700 800 900 Start up with EN 3.7 3.6 ACT4065A-005 ACT4065A-004 3.8 Maximum CC Current (mA) 300 Feedback Voltage (mV) Input Voltage (V) VIN = 12V V0UT = 5V ILOAD = 2A 3.5 CH1 3.4 CH2 3.3 3.2 3.1 3 20 30 40 50 60 70 CH1: EN, 1V/div CH2: VOUT, 1V/div TIME: 10ms/div Duty Cycle Innovative PowerTM -8- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4065A ® Rev 0, 23-Apr-12 PACKAGE OUTLINE SOP-8 PACKAGE OUTLINE AND DIMENSIONS D c E1 E L SYMBOL θ 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 4.780 5.000 0.188 0.197 E 3.800 4.000 0.150 0.157 E1 5.800 6.300 0.228 0.248 e A A2 B A1 e DIMENSION IN MILLIMETERS 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 firstname.lastname@example.org or visit http://www.active-semi.com. ® is a registered trademark of Active-Semi. Innovative PowerTM -9- www.active-semi.com Copyright © 2012 Active-Semi, Inc.