ACT4012ASH-T

ACT4012A Rev0, 16-May-08 Wide Input 1.5A Step Down Converter FEATURES • • • • • • • • • • 1.5A Output Current Up to 94% Efficiency Up to 20V Input Range 10µA 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 ACT4012A is a current-mode step-down DC/DC converter that generates up to 1.5A output 420kHz switching frequency. The device utilizes Active-Semi’s proprietary ISOBCD20 process for operation with input voltages up to 20V. Consuming only 10µA in shutdown mode, the ACT4012A is highly efficient with peak efficiency at 94% when in operation. Protection features include cycle-by-cycle current limit, thermal shutdown, and frequency foldback at short circuit. The ACT4012A 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 S-Top Boxes Telecom Power Supplies DSL and Cable Modems and Routers Termination Supplies TYPICAL APPLICATION CIRCUIT VIN 12V BS IN SW 5V/1.5A ACT4012A ENABLE EN G FB COMP + Innovative PowerTM -1- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT4012A Rev0, 16-May-08 ORDERING INFORMATION PART NUMBER ACT4012ASH ACT4012ASH-T TEMPERATURE RANGE -40°C to 85°C -40°C to 85°C PACKAGE SOP-8 SOP-8 PINS 8 8 PACKING TUBE TAPE & REEL PIN CONFIGURATION BS 1 8 N/C IN 2 7 EN ACT4012ASH SW 3 6 COMP G 4 5 FB SOP-8 PIN DESCRIPTIONS PIN NUMBER 1 2 3 4 5 6 7 8 PIN NAME BS IN SW G FB COMP EN N/C PIN DESCRIPTION Bootstrap. This pin acts as the positive rail for the high-side switch’s gate driver. Connect a 10nF between this pin and SW. Input Supply. Bypass this pin to G with a low ESR capacitor. See Input Capacitor in Application Information section. Switch Output. Connect this pin to the switching end of the inductor. Ground and Heat sink. Connect to a large, uncovered PCB copper area for best heat dissipation. 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 Compensation Technique in 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. EN pin has a small internal pull-up current to IN when pin is not connected. Not Connected. Innovative PowerTM -2- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT4012A Rev0, 16-May-08 ABSOLUTE MAXIMUM RATINGS PARAMETER IN to G EN to G SW to G BS to G FB, COMP to G Continuous SW Current Junction to Ambient Thermal Resistance (θJA) Maximum Power Dissipation Operating Junction Temperature Storage Temperature Lead Temperature (Soldering, 10 sec) VALUE -0.3 to 25 -0.3 to VIN +0.3 -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 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 = 25°C, 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 Innovative PowerTM SYMBOL VIN VFB RONH RONL TEST CONDITIONS VOUT = 5V, ILOAD = 0A to 1.5A 4.75V ≤ VIN ≤ 20V MIN 7.5 1.261 TYP 1.293 0.5 13.5 MAX 20 1.325 UNIT V V Ω Ω VEN = 0 ILIM GCOMP GEA AVEA fSW VFB = 0 DMAX VFB = 1.1V 310 ∆ICOMP = ±10µA 1.8 0 2.7 1.5 565 4000 420 50 90 14 10 µA A A/V µA/V V/V 530 kHz kHz % % Hysteresis = 0.1V Pin pulled up to IN when left unconnected VEN = 0 VEN = 3V, VFB = 1.4V Hysteresis = 10°C -3- 0.7 1 2 10 0.85 160 1.3 V µA 20 µA mA °C www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT4012A Rev0, 16-May-08 FUNCTIONAL BLOCK DIAGRAM IN 2µA ENABLE REGULATOR & REFERENCE EN BS CURRENT SENSE AMPLIFIER + - COMP ERROR AMPLIFIER 1.293V FB + + - + PWM COMP - 0.5 Ω HIGH-SIDE POWER SWITCH SW FOLDBACK CONTROL OSCILLATOR & RAMP LOGIC 13 Ω LOW-SIDE POWER SWITCH THERMAL SHUTDOWN G FUNCTIONAL DESCRIPTION As seen in Functional Block Diagram, the ACT4012A 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 2.6V. The Oscillator normally switches at 420kHz. However, if FB voltage is less than 0.7V, then the switching frequency decreases until it reaches a minimum of 50kHz at VFB = 0.5V. Shutdown Control The ACT4012A has an enable input EN for turning the IC on or off. When EN is less than 0.7V, the IC is 10µA 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 high voltage input that can with stand voltages up to VIN. Thermal Shutdown The ACT4012A automatically turns off when its junction temperature exceeds 160°C. Innovative PowerTM -4- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT4012A Rev0, 16-May-08 APPLICATIONS INFORMATION Output Voltage Setting Figure 1: Output Voltage Setting VOUT ACT4012A FB RFB2 RFB1 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 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 the 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 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: 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: L= VOUT × (V IN − VOUT ) V IN f SW I OUTMAX K RIPPLE + VIN 32 × fSW LC OUT 2 (3) (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 × (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. Table 1: Typical Inductor Values VOUT L 1.5V 7.5µH 1.8V 10µH 2.5V 12µH 3.3V 15µH 5V 22µH where IOUTMAX is the maximum output current, KRIPis 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. 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. PLE 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 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. Innovative PowerTM -5- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT4012A Rev0, 16-May-08 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 15kΩ, the equation for CCOMP is: C COMP = 1 .8 × 10 −5 R COMP (F) (10) COMP ACT4012A CCOMP 1 CCOMP2 If RCOMP is limited to 15kΩ, then the actual cross over frequency is 3.4 / (VOUTCOUT). Therefore: CCOMP = 1.2 ×10−5 VOUTCOUT (F) (11) RCOMP : CCOMP2 is needed only for high ESR output capacitor The feedback system 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 ⎞ RESRCOUT ≥ Min⎜ ,0.012 × VOUT ⎟ (Ω) ⎜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 f P1 = 2 π AVEA C COMP The second pole P2 is the output pole: fP 2 = I OUT 2 π VOUT 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: f Z1 = 1 2πRCOMP CCOMP2 (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 2π R COMP C COMP2 COUT 22µF Ceramic 22µF Ceramic 22µF Ceramic 47µF SP CAP 47µF SP CAP 47µF SP CAP 470µF/6.3V/30mΩ 470µF/6.3V/30mΩ 470µF/6.3V/30mΩ RCOMP 12kΩ 15kΩ 15kΩ 15kΩ 15kΩ 15kΩ 15kΩ 15kΩ 15kΩ CCOMP CCOMP2 1.5nF 1.5nF 1.5nF 1.5nF 1.8nF 2.7nF 15nF 22nF 27nF None None None None None None 1nF 1nF None (8) Follow the following steps to compensate the IC: STEP 1. Set the cross over frequency at 1/10 of the switching frequency via RCOMP: R COMP = 2π VOUT C OUT f SW 10 G EA GCOMP × 1 .3V ( Ω) (9) = 2 × 10 8 V OUT C OUT : CCOMP2 is needed for high ESR output capacitor. Figure 3 shows an example ACT4012A application circuit generating a 5V/1.5A output. but limit RCOMP to 15kΩ maximum. Innovative PowerTM -6- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT4012A Rev0, 16-May-08 Figure 3: ACT4012A 5V/1.5A Output Application VIN 7.5V to 20V IN EN G BS SW C3 10nF L1 22µH/2A 5V/1.5A R1 37k VOUT ACT4012A ENABLE FB COMP C2 1.5nF R3 15k C5 (OPTIONAL) + C1 10µF/ 25V R2 13k D1 C4 22µF/10V Ceramic : D1 is a 30V, 2A Schottky diode with low forward voltage, an IR 20BQ030 or SK23 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 PowerTM -7- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT4012A Rev0, 16-May-08 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 3, unless otherwise specified.) Efficiency vs. Load 100 95 90 95 90 ACT4012A-001 Efficiency vs. Load ACT4012A-002 VIN = 8V Efficiency (%) 85 80 75 70 65 60 55 0.1 0.3 0.5 0.7 0.9 VOUT = 5V L= 22µH COUT = 22µF/cera 1.1 1.3 1.5 VIN = 12V VIN = 20V VIN = 8V Efficiency (%) 85 80 VIN = 12V 75 VIN = 20V 70 65 60 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 VOUT = 3.3V L= 15µH COUT = 22µF/cera Load (A) Load (A) Surface Temperature vs. Load 100 5.4 5.2 ACT4012A-003 Output Voltage vs. Input Voltage ACT4012A-004 IOUT = 0.5A Surface Temperature (°C) 80 VIN = 12V 60 VIN = 20V 40 VIN = 8V Output Voltage (V) 5.0 4.8 4.6 4.4 4.2 IOUT = 1A IOUT = 1.5A 20 0.1 0.3 0.5 0.7 0.9 1.1 1.3 1.5 4.0 6 8 10 12 14 16 18 20 Load (A) Input Voltage (V) Feedback Voltage vs. Junction Temperature Shutdown Supply current (µA) 1.30 25 ACT4012A-005 Shutdown Supply current vs. Input Voltage ACT4012A-006 Feedback Voltage (V) 1.29 20 1.28 15 1.27 10 1.26 -40 0 40 80 120 5 0 12 16 20 Junction Temperature (°C) Input Voltage (V) Innovative PowerTM -8- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT4012A Rev0, 16-May-08 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 3, unless otherwise specified.) Switching Frequency vs. Input Voltage 430 ACT4012A-007 Switching Frequency (kHz) 425 420 415 410 8 12 16 20 Input Voltage (V) Innovative PowerTM -9- www.active-semi.com Copyright © 2008 Active-Semi, Inc. ACT4012A Rev0, 16-May-08 PACKAGE OUTLINE SOP-8 PACKAGE OUTLINE AND DIMENSIONS C D SYMBOL A A1 A2 B θ 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 C D E E1 e L θ 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 PowerTM - 10 - www.active-semi.com Copyright © 2008 Active-Semi, Inc.