ACT4070B Rev 0, 23-Apr-12 Wide Input 3A Step Down Converter FEATURES GENERAL DESCRIPTION • • • • • • • • • • • • • • ACT4070B is a wide input voltage step-down DC/DC converter that provides up to 3A output current at 300kHz switching frequency. ACT4070B is a replacement part for ACT4070 with advanced features such as lower standby current and higher light load efficiency. ACT4070B can be dropped into ACT4070 socket with only feedback resistance value changed. 3A Output Current Up to 95% Efficiency 6.5V to 30V Input Range 100µA Shutdown Supply Current 4mA Standby Input Current 300kHz Switching Frequency ACT4070B’s protection features include Cycle-byCycle current limit, thermal shutdown, and frequency foldback at over current and short circuit. The devices are available in a SOP-8EP package and require very few external devices for operation. Output Voltage Up to 12V Cycle-by-Cycle Current Limit Protection Thermal Shutdown Protection Internal Soft Start Function Frequency Fold Back at Short Circuit NOTE: Stability with Wide Range of Capacitors ∗ Including Low ESR Ceramic Capacitors ACT4070B ACT4070. is the replacement part for 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 Efficiency vs. Load Current ACT4070B-001 100 VIN = 12V Efficiency (%) 80 60 VIN = 24V 40 20 VOUT = 5V 0 1 10 100 1000 10000 Load Current (mA) Innovative PowerTM -1- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4070B Rev 0, 23-Apr-12 ORDERING INFORMATION PART NUMBER TEMPERATURE RANGE PACKAGE PINS PACKING ACT4070BYH -40°C to 85°C SOP-8/EP 8 TUBE ACT4070BYH-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 GND with a low ESR capacitor. See Input Capacitor in Application Information section. 3 SW 4 GND 5 FB 6 COMP Compensation Pin. See Compensation Technique in Application Information section. 7 EN Enable Input. When higher than 1.6V, this pin turns the IC on. When lower than 1.5V, this pin turns the IC 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 Innovative PowerTM PIN DESCRIPTION Switch Output. Connect this pin to the switching end of the inductor. Ground. 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. -2- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4070B Rev 0, 23-Apr-12 ABSOLUTE MAXIMUM RATINGSc PARAMETER VALUE UNIT IN to GND -0.3 to + 34 V EN to GND -0.3 to VIN + 0.3 V SW to GND -1 to VIN + 1 V BS to SW -0.3 to + 7 V FB, COMP to GND -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) 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= 25°C, unless otherwise specified.) PARAMETER Input Voltage SYMBOL VIN VIN UVLO Turn-on Voltage TEST CONDITIONS MIN VOUT = 2.5V, ILOAD = 0A to 3A TYP 6.5 30 V 5.5 V VFB 0.792 0.808 0.824 V High-Side Switch On Resistance RONH 130 mΩ Low-Side Switch On Resistance RONL 7.9 Ω Feedback Voltage Input Voltage Rising MAX UNIT SW Leakage High-Side Switch Peak Current Limit VEN = 0, VIN = 12V, VSW = 0V ILIM COMP to Current Limit Transconductance GCOMP Error Amplifier Transconductance GEA Error Amplifier DC Gain AVEA Switching Frequency 10 µA Duty Cycle = 50% 3.7 A ΔILOAD/ΔICOMP 5.25 A/V ΔICOMP = ±10µA 650 µA/V 4000 V/V fSW Short Circuit Switching Frequency Maximum Duty Cycle 1 250 VFB = 0V DMAX Minimum on Time 330 kHz 44 kHz 88 % 200 ns Enable Threshold Voltage Hysteresis = 0.1V Enable Pull Up Current Pin pulled up to VIN when left unconnected 4 Supply Current in Shutdown VEN = 0 75 115 µA IC Supply Current in Operation VFB = 1.2V, not switching 0.675 1 mA Thermal Shutdown Temperature Hysteresis = 20°C Innovative PowerTM -3- 1.47 300 1.6 150 1.73 V µA °C www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4070B Rev 0, 23-Apr-12 FUNCTIONAL BLOCK DIAGRAM FUNCTIONAL DESCRIPTION As seen in the Functional Block Diagram, the ACT4070B 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 PowerTM -4- The COMP voltage is the integration of the error between 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. The Oscillator normally switches at 300kHz. However, if FB voltage is less than 0.6V, then the switching frequency decreases until it reaches a typical value of 36kHz at VFB = 0V. Shutdown Control The ACT4070B has an enable input EN for turning the IC on or off. When EN is less than 1.5V, the IC is in 100μA low current shutdown mode and output is discharged through the Low-Side Power Switch. When EN is higher than 1.6V, 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. Thermal Shutdown The ACT4070B automatically turns off when its junction temperature exceeds 160°C and then restarts once the temperature falls to 150°C. www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4070B Rev 0, 23-Apr-12 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 OUT ⎞ -1 ⎟ R FB 1 = R FB2 ⎜ ⎝ 0 . 808 V ⎠ (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 8.5μH 15μH 15μH Innovative PowerTM (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 -5- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4070B Rev 0, 23-Apr-12 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 C COMP = 2 . 83 x 10 R COMP C COMP = 6 . 45 x10 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 . 77 x 10 ≥ Min ⎜⎜ C OUT ⎝ (4) G EA 2 π A VEA C COMP CCOMP = (5) I OUT 2 π VOUT C OUT (6) 1 (Ω) ⎞ ,0 . 006 V OUT ⎟⎟ ⎠ (12) COUT R ESROUT RCOMP (13) Table 2 shows some calculated results based on the compensation method above. (7) 2 πRCOMP CCOMP −6 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 = (11) And the proper value for CCOMP2 is: The second pole P2 is the output pole: fP 2 = (F) V OUT C OUT R ESROUT The dominant pole P1 is due to CCOMP: fP 1 = −6 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: c: CCOMP2 is needed only for high ESR output capacitor AVDC (10) (F) If RCOMP is limited to 15kΩ, then the actual cross over frequency is 4.8/(VOUTCOUT). Therefore: c 0 . 808 V = AVEA G COMP I OUT 5 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 CCOMP2c 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 = R COMP 1 (8) 2 πRCOMP CCOMP2 = 2 π V OUT C OUT f SW 10 G EA G COMP 0 . 808 V = 5 . 12 x 10 7 V OUT C OUT (Ω) (9) c: CCOMP2 is needed for board parasitic and high ESR output capacitor. Figure 3 shows a sample ACT4070B application circuit generating a 2.5V/3A output. but limit RCOMP to 15kΩ maximum. Innovative PowerTM -6- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4070B Rev 0, 23-Apr-12 Figure 3: ACT4070B 5V/3A Output Applicationc Table 3: BOM List for 5V/3A Car Charger ITEM REFERENCE DESCRIPTION MANUFACTURER QTY 1 U1 IC, ACT4070B, SOP-8EP Active-Semi 1 2 C1 Capacitor, Ceramic, 10µF/50V, 1206, SMD Murata, TDK 1 3 C2 Capacitor, Ceramic, 4.7nF/25V, 0603, SMD Murata, TDK 1 4 C3 Capacitor, Ceramic, 10nF/25V, 0603, SMD Murata, TDK 1 5 C4 Capacitor, Ceramic, 22µF/10V, 0805, SMD Murata, TDK 1 6 L1 Inductor, 15µH, 4A, 20%, SMD Sunlord 1 7 D1 Diode, Schottky, 40V/3A, SK34 Diodes 1 8 R1 Chip Resistor, 51kΩ, 0603, 1% Murata, TDK 1 9 R2 Chip Resistor, 9.76kΩ, 0603, 1% Murata, TDK 1 10 R3 Chip Resistor, 12kΩ, 0603, 5% Murata, TDK 1 Innovative PowerTM -7- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4070B Rev 0, 23-Apr-12 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 3, unless otherwise specified.) Efficiency vs. Load Current Shutdown Current vs. Input Voltage Shutdown Current (µA) Efficiency (%) VIN = 24V 40 20 ACT4070B-003 VIN = 12V 80 60 120 ACT4070B-002 100 100 80 60 40 20 VOUT = 5V 0 1 10 100 1000 0 10000 Load Current (mA) 5 10 15 25 20 30 Input Voltage (V) Load Transient Response Load Transient Response VIN = 24V V0UT = 5V CH1 ACT4070B-005 CH1 ACT4070B-004 VIN = 12V V0UT = 5V CH2 CH2 CH1: IOUT, 1A/div CH2: VOUT, 200mV/div TIME: 400µs/div CH1: IOUT, 1A/div CH2: VOUT, 200mV/div TIME: 400µs/div Maximum Peak Current vs. Duty Cycle Maximum CC Current (A) ACT4070B-006 4.5 4.2 3.9 3.6 3.3 3 20 30 40 50 60 70 Duty Cycle Innovative PowerTM -8- www.active-semi.com Copyright © 2012 Active-Semi, Inc. ACT4070B Rev 0, 23-Apr-12 PACKAGE OUTLINE SOP-8/EP PACKAGE OUTLINE AND DIMENSIONS SYMBOL DIMENSION IN MILLIMETERS DIMENSION IN INCHES MIN MAX MIN MAX A 1.350 1.700 0.053 0.067 A1 0.000 0.100 0.000 0.004 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 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. ® is a registered trademark of Active-Semi. Innovative PowerTM -9- www.active-semi.com Copyright © 2012 Active-Semi, Inc.