ACT4012A ACTIVE-SEMI | Alldatasheet

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Technical content

Innovative Products. Active Solutions. - 1 - www.active-semi.com Copyright © 2006 Active-Semi, Inc.

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
  • 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 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 opera- tion. TYPICAL APPLICATION CIRCUIT ACT4012A Rev PrA, 21-Nov-07 Preliminary Information - All Information Subject to Change Wide Input 1.5A Step Down Converter Wide Input 1.5A Step Down Converter

Innovative Products. Active Solutions. - 2 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev PrA, 21-Nov-07

ORDERING INFORMATION

PART NUMBER TEMPERATURE RANGE PACKAGE PINS PACKING ACT4012ASH -40°C to 85°C SOP-8 8 TUBE ACT4012ASH-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 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 Switch Output. Connect this pin to the switching end of the inductor. 4 G Ground and Heat sink. Connect to a large, uncovered PCB copper area for best heat dissipation. 5 FB Feedback Input. The voltage at this pin is regulated to 1.293V. Connect to the resis- tor 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. EN pin has a small internal pull-up current to IN when pin is not connected. 8 N/C Not Connected. SOP-8

Innovative Products. Active Solutions. - 3 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev PrA, 21-Nov-07 ABSOLUTE MAXIMUM RATINGSc PARAMETER VALUE UNIT IN to G -0.3 to 25 V SW to G -1 to VIN + 1 V BS to G VSW - 0.3 to VSW + 8 V FB, COMP to G -0.3 to 6 V Continuous SW Current Internally Limited A Junction to Ambient Thermal Resistance (θ JA) 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 EN to G -0.3 to V IN +0.3 V

ELECTRICAL CHARACTERISTICS

(VIN = 12V, TA = 25°C, unless otherwise specified.) PARAMETER SYMBOL TEST COND ITIONS MIN TYP MAX UNIT Input Voltage V IN V OUT = 5V, ILOAD = 0A to 1.5A 7.5 20 V Feedback Voltage V FB 4.75V ≤ VIN ≤ 20V 1.261 1.293 1.325 V High-Side Switch On Resistance R ONH 0.5 Ω Low-Side Switch On Resistance R ONL 13.5 Ω SW Leakage V EN = 0 0 10 µA Current Limit I LIM 1.8 2.7 A COMP to Current Limit Transconductance GCOMP 1.5 A/V Error Amplifier Transconductance G EA ∆ICOMP = ±10µA 565 µA/V Error Amplifier DC Gain A VEA 4000 V/V Switching Frequency f SW 310 420 530 kHz Short Circuit Switching Frequency V FB = 0 50 kHz Maximum Duty Cycle D MAX V FB = 1.1V 90 % Minimum Duty Cycle 14 % Enable Threshold Voltage Hy steresis = 0.1V 0.7 1 1.3 V Enable Pull-Up Current Pin pulled up to IN when left unconnected 2 µA Supply Current in Shutdown V EN = 0 10 20 µA IC Supply Current in Operation V EN = 3V, VFB = 1.4V 0.85 mA Thermal Shutdown Temperature Hysteresis = 10°C 160 °C c: Do not exceed these limits to prevent damage to the device. Exposure to absolute maximum rati ng conditions for long periods m ay affect device reliability.

Innovative Products. Active Solutions. - 4 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev PrA, 21-Nov-07 FUNCTIONAL BLOCK DIAGRAM FUNCTIONAL DESCRIPTION As seen in Functional Block Diagram , the ACT4012A is a current mode pulse width modula- tion (PWM) converter. Th e converter operates as follows: A switching cycle starts when the rising edge of the Oscillator clock output c auses 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 fiel d. 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 continue s 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 V SW + 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 2.6V. The Oscillator normally sw itches at 420kHz. How- ever, if FB voltage is less than 0.7V, then the switching frequency decreases until it reaches a minimum of 50kHz at V FB = 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 V IN. Thermal Shutdown The ACT4012A automatically turns off when its junction temperature exceeds 160°C.

Innovative Products. Active Solutions. - 6 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev PrA, 21-Nov-07 STABILITY COMPENSATION STEP 2. Set the zero f Z1 at 1/4 of the cross over frequency. If R COMP is less than 15k Ω, the equation for CCOMP is: If R COMP is limited to 15k Ω, 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 C COMP2 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 C OUT R COMP C COMP C COMP2 c 2.5V 22µF Ceramic 12k Ω 1.5nF None 3.3V 22µF Ceramic 15k Ω 1.5nF None 5V 22µF Ceramic 15k Ω 1.5nF None 2.5V 47µF SP CAP 15k Ω 1.5nF None 3.3V 47µF SP CAP 15k Ω 1.8nF None 5V 47µF SP CAP 15k Ω 2.7nF None 2.5V 470µF/6.3V/30m Ω 15k Ω 15nF 1nF 3.3V 470µF/6.3V/30m Ω 15k Ω 22nF 1nF 5V 470µF/6.3V/30m Ω 15k Ω 27nF None c: CCOMP2 is needed for high ESR output capacitor. Figure 3 shows an example ACT4012A application circuit gener- ating a 5V/1.5A output. COMP ESRCOUTOUT 2COMP R RCC = (13) Figure 2: Stability Compensation (10) (F) COMP COMP R 108.1C −×= (11) (F) OUTOUT COMP CV102.1C −×= c: CCOMP2 is needed only for high ESR output capacitor The feedback system of t he 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 C COMP: And finally, the third pole is due to R COMP and CCOMP2 (if CCOMP2 is used): Follow the following steps to compensate the IC: STEP 1. Set the cross over frequency at 1/10 of the switching frequency via R COMP: 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 CV102 ×=

(4) COMPVEA OUT VDC GAI V3.1A = (5) COMPVEA EA CAπ2 Gf = (6) OUTOUT OUT CVπ2 If = (12) (Ω) ⎟⎟ ⎛ ××≥ OUT OUT ESRCOUT V012.0,C 101.1MinR (7) COMP2COMP CRπ2 1f =

Innovative Products. Active Solutions. - 7 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev PrA, 21-Nov-07 Figure 3: ACT4012A 5V/1.5A Output Applicationc c: D1 is a 30V, 2A Schottky diode with low forward voltage, an IR 20BQ030 or SK23 equivalent. C4 can be either a ceramic capacit or (Panasonic ECJ-3YB1C226M) or SP-CAP (Specialty Polymer) Aluminum Electrol ytic Capacitor such as Panasonic EEFCD0J470XR. The SP-Cap is based on aluminum electrolyt ic capacitor technology, but uses a solid pol ymer electrolyte and has very stable cap aci- tance characteristics in both operating temperature and frequency compared to ceramic, polymer, and low ESR tantalum capacitors.

Innovative Products. Active Solutions. - 8 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev PrA, 21-Nov-07 TYPICAL PERFORMANCE CHARACTERISTICS Load (A) 0.1 0.5 1.1 1.5 ACT4012A-002 0.1 Load (A) 0.3 0.5 0.7 0.9 ACT4012A-001 100 Efficiency vs. Load (Circuit of Figure 3, unless otherwise specified.) Input Voltage (V) Shutdown Supply current (µA) ACT4012A-006 0 12 16 20 Shutdown Supply current vs. Input Voltage Load (A) Surface Temperature (°C) ACT4012A-003 0.1 0.3 0.7 0.9 Surface Temperature vs. Load 1.3 100 Junction Temperature (°C) 1.29 ACT4012A-005 -40 0 40 80 Feedback Voltage vs. Junction Temperature 120 1.30 1.28 1.27 1.26 1.1 1.3 1.5 Efficiency (%) Efficiency (%) Feedback Voltage (V) 0.3 0.7 0.9 1.3 VOUT = 3.3V L= 15µH COUT = 22µF/cera 0.5 1.1 1.5 VIN = 12V VIN = 20V VIN = 8V VOUT = 5V L= 22µH COUT = 22µF/cera VIN = 8V VIN = 12V VIN = 20V Efficiency vs. Load 5.0 Output Voltage (V) ACT4012A-004 6 10 14 Output Voltage vs. Input Voltage 5.4 4.6 4.2 4.0 5.2 4.8 4.4 12 8 Input Voltage (V) 18 16 IOUT = 0.5A IOUT = 1A IOUT = 1.5A VIN = 12V VIN = 20V VIN = 8V

Innovative Products. Active Solutions. - 9 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev PrA, 21-Nov-07 Input Voltage (V) 12 16 20 ACT4012A-007 425 430 415 410 Switching Frequency (kHz) Switching Frequency vs. Input Voltage 420 TYPICAL PERFORMANCE CHARACTERISTICS (Circuit of Figure 3, unless otherwise specified.)

Innovative Products. Active Solutions. - 10 - www.active-semi.com Copyright © 2006 Active-Semi, Inc. Rev PrA, 21-Nov-07 Active-Semi, Inc. reserves the right to modify the circuitry or specifications without notice. User s should evaluate each product to make sure that it is suitable for their applicat ions. Active-Semi products are not intended or authorized for use as critical components in life-support dev ices 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, In c. 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

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