APW7179 Dual 1.5MHz, 1A Synchronous Step-Down Converter Features • • • • • • • • • • • • General Description The APW7179 consists of two independent 1.5MHz constant frequency, current mode, and PWM step-down 1A Output Current on Each Channel 2.7V to 5.5V Input Voltage Range converters. Each converter integrates a main switch with a synchronous rectifier for high efficiency without an ex- 1.5MHz Constant Frequency Operation Low Dropout Operation at 100% Duty Cycle ternal Schottky diode. The APW7179 is ideal for powering portable equipment that runs from a single cell Lithium- Synchronous Topology 0.6V Low Reference Voltage Ion (Li+) battery. Each converter can supply 1A of load current from a 2.7V to 5.5V input voltage. The output volt- Current Mode Operation Over-Temperature Protection age can be regulated as low as 0.6V. The APW7179 can also run at 100% duty cycle for low dropout applications. Over-Current Protection Up to 94% Efficiency Pin Configuration Internally Compensated Lead Free and Green Devices Available APW7179 (RoHS Compliant) Applications • • IN2 1 SW2 2 11 NC GND2 3 10 FB2 FB1 4 NC TV Tuner/Box 12 EN2 TDFN3x3-12 (Top View) 5 EN1 6 9 GND1 8 SW1 7 IN1 Portable Instrument Exposed pad on backside Ordering and Marking Information Package Code QB : TDFN3x3-12 Temperature Range I : -40 to 85 oC Handling Code TR : Tape & Reel Assembly Material G : Halogen and Lead Free Device APW7179 Assembly Material Handling Code Temperature Range Package Code APW7179 QB: APW 7179 XXXXX XXXXX - Date Code Note: ANPEC lead-free products contain molding compounds/die attach materials and 100% matte tin plate termination finish; which are fully compliant with RoHS. ANPEC lead-free products meet or exceed the lead-free requirements of IPC/JEDEC J-STD-020D for MSL classification at lead-free peak reflow temperature. ANPEC defines “Green” to mean lead-free (RoHS compliant) and halogen free (Br or Cl does not exceed 900ppm by weight in homogeneous material and total of Br and Cl does not exceed 1500ppm by weight). ANPEC reserves the right to make changes to improve reliability or manufacturability without notice, and advise customers to obtain the latest version of relevant information to verify before placing orders. Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 1 www.anpec.com.tw APW7179 Absolute Maximum Ratings Symbol (Note 1) Parameter VIN1/IN2 Input Supply Voltage (IN1/IN2 to GND1/GND2) Rating Unit -0.3 ~ 6 V VFB1/FB2 Voltage on FB1 and FB2 (FB1/FB2 to GND1/GND2) -0.3 ~ VIN1/IN2+0.3 V VEN1/EN2 Voltage on EN1 and EN2 (EN1/EN2 to GND1/GND2) -0.3 ~ VIN1/IN2+0.3 V VSW1/SW2 Voltage on SW1 and SW2 (SW1/SW2 to GND1/GND2) -0.3 ~ VIN1/IN2+0.3 V ISW_PEAK Peak SW Current 1.8 A 2 W 150 °C -65 ~ 150 °C 260 °C o PD Maximum Power Dissipation (TA=25 C) TJ Maximum Junction Temperature TSTG Storage Temperature Range TSDR Maximum Lead Soldering Temperature, 10 Seconds Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Thermal Characteristics Symbol θJA θJC Parameter Typical Value Junction-to-Ambient Resistance in Free Air (Note 2) Unit 50 TDFN3x3-12 °C/W Junction-to-Case Resistance in Free Air 12 TDFN3x3-12 Note 2: θJA is measured on with the device mounted the PCB with top-layer pad of approximate 1” square of 1 oz copper. Recommended Operating Conditions Symbol VIN1/IN2 R2/R4 Parameter Input Supply Voltage (IN1/IN2 to GND1/GND2) Feedback Resistance IOUT Output Current TA TJ (Note 3) Range Unit 2.7 ~ 5.5 V ~ 300 kΩ 0 ~ 1 A Operating Ambient Temperature -40 ~ 85 °C Operating Junction Temperature -40 ~ 125 °C Note 3: Please refer to the typical application circuit. Electrical Characteristics The denotes the specifications that apply over VIN=3.6V and TA =25°C, unless otherwise specifications. Symbol Parameter APW7179 Test Conditions Unit Min. Typ. Max. 2.7 - 5.5 V VIN1/IN2 Each Converter Input Voltage Range IFB1/FB2 FB1/FB2 Input Current VFB1/FB2=0.6V -30 - 30 nA Each Converter Reference Voltage IOUT=0mA~1A 0.588 0.6 0.612 V Each Converter Reference Voltage Line Regulation -40oC≤TA≤85 oC - 0.04 - %/V Each Converter Peak Inductor Current VIN1/IN2=3.3V, VFB=0.5V or VOUT=90%, Duty cycle < 35% 1.4 1.6 - A VREF1/REF2 ∆VREF1/REF2 IPK Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 2 www.anpec.com.tw APW7179 Electrical Characteristics (Cont.) The denotes the specifications that apply over VIN=3.6V and TA =25°C, unless otherwise specifications. APW7179 Symbol Parameter Test Conditions Unit Min. Typ. Max. Each Converter Load Regulation IOUT=10mA~1A - 0.5 - % IDD Each Converter Quiescent Current VFB=0.7V - 30 50 µA ISD Each Converter Quiescent Current in Shutdown VEN1/EN2=0V, VIN=4.2V - - 1 µA fOSC Each Converter Oscillator Frequency VFB=0.6V 1.2 1.5 1.8 MHz fOSC_FFB Each Converter Frequency Foldback VFB=0V - 210 - kHz RDS-P Each Converter On Resistance of PMOSFET ISW =100mA - 0.28 - Ω RDS-N Each Converter On Resistance of NMOSFET ISW =-100mA - 0.25 - Ω VEN1/EN2 Each Converter Enable Threshold 0.4 - 1 TOTP Thermal Shutdown Threshold - Thermal Shutdown Hysteresis Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 - 3 150 50 V - o - o C C www.anpec.com.tw APW7179 Typical Operating Characteristics (Refer to the application circuit in the section “Typical Application Circuits”, VIN=3.6V, VOUT=1.8V, TA=25oC unless Efficiency vs. Load Current 100 100 90 90 80 80 Efficiency (%) Efficiency (%) otherwise specified ) Efficiency vs. Load Current 70 60 VIN=3.3V VIN=5V 50 40 60 50 VOUT = 1.2V L = 2.2µH COUT = 10µF 30 20 20 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0 1 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 Load Current, IOUT(A) Supply Voltage vs. ON Resistance 40 0.35 35 0.30 30 ON Resistance(Ω) Quiescent Current, IDD(µA) 1 Load Current, IOUT(A) Supply Voltage v.s. Quiescent Current 25 20 15 10 RP-FET 0.25 0.20 RN-FET 0.15 0.10 0.05 5 0 VIN=3.3V VIN=5V 40 VOUT = 1.8V L = 2.2µH COUT = 10µF 30 70 2 2.5 3 3.5 4 4.5 5 5.5 0.00 6 Supply Voltage, V IN(V) 2 2.5 3 3.5 4 4.5 5 5.5 6 Supply Voltage, VIN(V) Supply Voltage v.s. Reference Voltage 0.65 Reference Voltage, VREF(V) 0.64 0.63 0.62 0.61 0.6 0.59 0.58 0.57 0.56 0.55 2 2.5 3 3.5 4 4.5 5 5.5 6 Supply Voltage, VIN (V) Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 4 www.anpec.com.tw APW7179 Operating Waveforms (Refer to the application circuit in the section “Typical Application Circuits”, VIN=3.6V, VOUT=1.8V, TA=25oC unless otherwise specified) Soft Start Load Transient Response 1A 1 VEN 300mA 1 VOUT ,1V/Div, DC 2 IOUT, 0.5A/Div, DC VOUT ,100mV/Div, AC 2 3 IIN, 200mA/Div L=2.2µH, VIN=5V, VOUT=1.8V, COUT=10µF L=2.2µH, VIN=5V, COUT=10µF Time: 100µs/Div Time: 100µs/Div Normal Operation 2.5V 1.5V VIN, 0.5V/Div 1 VSW ,2V/Div, DC 2 VOUT ,20mV/Div, AC VOUT,200mV/Div,AC IL, 500mV/Div, DC 3 L=2.2µH, VINI=5V, VOUT=1.2V, COUT=10µF = 100mA OUT Time: 500ns/Div Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 5 www.anpec.com.tw APW7179 Pin Description PIN FUNCTION NO. NAME 1 IN2 2 SW2 3 GND2 Channel 2 Supply Input. Bypass to the GND2 with a 4.7µF or greater ceramic capacitor. Channel 2 Power Switch Output. Inductor connection to drains of the internal PMOSFET and NMOSFET switches. Ground 2. Connected the exposed pad to the GND2. Channel 1 Feedback Input. Connect FB1 to the center point of the external resistor divider. The feedback voltage is 0.6V. 4 FB1 5, 11 NC No Internal Connection. 6 EN1 Channel 1 Enable Control Input. Drive EN1 above 1V to turn on the Channel 1. Drive EN1 below 0.4V to turn it off. In shutdown situation, all functions are disabled to decrease the supply current below 1µA. Don’t left this pin floating. 7 IN1 Channel 1 Supply Input. Bypass to the GND1 with a 4.7µF or greater ceramic capacitor. 8 SW1 9 GND1 10 FB2 12 EN2 Exposed Pad NC Channel 1 Power Switch Output. Inductor connection to drains of the internal PMOSFET and NMOSFET switches. Ground 1. Connected the exposed pad to the GND1. Channel 2 Feedback Input. Connect FB2 to the center point of the external resistor divider. The feedback voltage is 0.6V. Channel 2 Enable Control Input. Drive EN2 above 1V to turn on the Channel 2. Drive EN2 below 0.4V to turn it off. In shutdown situation, all functions are disabled to decrease the supply current below 1µA. Don’t left this pin floating. No Internal Connection. Connecting this pad to GND1 and GND2. Block Diagram IN1/IN2 Shutdown Control g EN1/EN2 Logic Control SW1/SW2 Gate Driver OverTemperature Protection Current Limit ∑ GND1/GND2 Oscillator ICMP FB1/FB2 COMP EAMP Softstart VREF 0.6V Diagram Represents 1/2 of the APW7179 Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 6 www.anpec.com.tw APW7179 Typical Application Circuit VIN1/IN2 CIN1 4.7µF R5 100kΩ IN1 VOUT1 1.2V 1A IN2 EN1 OFF ON R6 100kΩ EN2 L1 2.2µH APW7179 SW2 FB1 10pF Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 VOUT2 3.3V 1A R3 300kΩ R1 150kΩ COUT1 10µF OFF ON L2 2.2µH SW1 CIN2 4.7µF R2 150kΩ COUT2 10µF FB2 GND1 GND2 R4 10pF 47kΩ 7 www.anpec.com.tw APW7179 Function Description Main Control Loop Junction Temperature (TJ ) during continuous thermal overload conditions, increasing the lifetime of the device. The APW7179 has dual independent constant frequency, current-mode PWM step-down converters. During nor- Enable/Shutdown mal operation, the internal P-channel power MOSFET is turned on each cycle when the oscillator sets an internal For each channel, driving EN to the ground places the RS latch and is turned off when an internal comparator (ICMP) resets the latch. The peak inductor current at which channel in shutdown mode. When in shutdown, the internal power MOSFETs are turned off, all internal circuitry ICMP resets the RS latch is controlled by the voltage on the COMP, which is the output of the error amplifier shuts down, and the quiescent supply current reduces to 1µA maximally. (EAMP). An external resistive divider connected between VOUT and ground allows the EAMP to receive an output Automoatic PFM/PWM mode Switch The APW7179 is a fixed frequency PWM peak current feedback voltage VFB at FB pin. When the load current increases, it causes a slightly decrease in VFB associated modulation control step-down converter. At light loads, the APW7179 will automatically enter in pulse frequency with the 0.6V reference, which in turn causes the COMP voltage to increase until the average inductor current matches the new load current. modulation operation to reduce the dominant switching losses. In PFM operation, the inductor current may reach Soft-Start zero or reverse on each pulse. A zero current comparator turns off the N-channel synchronous MOSFET, forcing DCM (Discontinuous Current Mode) operation at light load. These controls get very low quiescent, help to main- Each channel in the APW7179 has a built-in soft-start to control the output voltage rise during start-up. During softstart, an internal ramp, connected to the one of the posi- tain high efficiency over the complete load range. tive inputs of the error amplifier, raise up to replace the reference voltage (0.6V typical) until the ramp voltage reaches the reference voltage. Short Circuit Protection For each channel, when the output is shortened to the ground, the frequency of the oscillator will be reduced to 210kHz. This lower frequency allows the inductor current to safely discharge, thereby preventing current runaway. The oscillator’s frequency will gradually increase to its designed rate when the feedback voltage on the FB again approaches 0.6V. Over-Temperature Protection (OTP) For each channel, the over-temperature circuit limits the junction temperature of the APW7179. When the junction temperature exceeds 150oC, a thermal sensor turns off the power MOSFETs, allowing the channels to cool down. The thermal sensor allows the converter to start a softstart process and to regulate the output voltage again after the junction temperature cools by 40οC. The OTP is designed with a 40οC hysteresis to lower the average Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 8 www.anpec.com.tw APW7179 Application Information IL Inductor Selection IOUT Due to the high switching frequency as 1.5MHz, the inductor value of the application of the APW7179 is usually in the range from 1µH to 4.7µH. The criterion of selecting IIN 0A a suitable inductor depends on its maximum current ripple. The maximum current ripple defines as 40% of the fully I(CIN) IIN 0A load current. In the APW7179 applications, the maximum value of current ripple is 400mA, the 40% of 1A. Calculate L by the equation (1): L= (VIN − VOUT ) ⋅ VOUT ⋅ VIN 1 ...............(1) ∆IL ⋅ fOSC 0A I(COUT) where fOSC is the switching frequency of APW7179 and ∆IL is the value of the maximum current ripple. It can be any I(Q1) value of current ripple that smaller than the maximum value you can accept. In order to perform high efficiency, selecting a low DC resistance inductor is a helpful way. Another important parameter is the DC current rating of IOUT 0A the inductor. The minimum value of DC current rating equals the full load value of 1A, and then plus the half of D*TS the current ripple. Choose inductors with suitable DC cur- PWM (1-D)*TS rent rating to ensure the inductors don’t operate in the saturation. 0A Figure-2 Input Capacitor Selection By observing the waveform of I(CIN), the RMS value of I(CIN) is The input capacitor must be able to support the maximum input operating voltage and maximum RMS input I(CIN ) = current. The Buck converter absorbs pulse current from input power source. [(I OUT ] ( − IIN ) ⋅ D + IIN ⋅ 1 − D 2 2 ) 2 .....( 2) Replace D and IIN by following relation: I(Q1) D= I(CIN) IIN Q1 L VIN CIN IIN = D ⋅ IOUT .........................( 4 ) I(L) Q2 VOUT ..............................(3) VIN I(COUT) COUT The RMS value of input capacitor current equal: IOUT I(CIN ) = IOUT ⋅ D(1 − D) ............(5) PWM When D=0.5, the RMS current of input capacitor will be maximum value. Use this value to choose the input capacitor with suitable current rating. Figure-1 Figure-1 shows a schematic of a Buck converter. The waveforms are shown as Figure-2. Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 9 www.anpec.com.tw APW7179 Application Information (Cont.) TS ∆VOUT = ∆IL ⋅ ESR + ⋅ 8 C OUT Output Capacitor Selection The output voltage ripple is a significant parameter to estimate the performance of a convertor. There are two .................(8) Thermal Consideration discrete components that affect the output voltage ripple to be bigger or smaller. It is recommended to use the APW7179 is a high efficiency switching converter, it means criterion mentioned in the "Inductor Selection" to choose a suitable inductor. Then, based on this known inductor less power loss transferred into heat. Due to the on resistance difference between internal power PMOSFET current ripple, the value and equivalent-series-resistance (ESR) of output capacitor will affect the output voltage ripple and NMOSFET, the power dissipation at high duty cycle is greater than the low duty cycle. The worst case in the to be smaller or larger. The output voltage ripple consists of two portions, one is the product of ESR and inductor dropout operation is the conduction loss dissipate mainly on the internal power PMOSFET. The power dissipation current ripple, the other portion is the function of the inductor current ripple and the output capacitance. Figure-3 is nearly defined as: PD = (IOUT ) [RDS−P ⋅ D + RDS−N ⋅ (1 − D)].......(9) 2 illustrates the waveform of the ripple voltage which is generated when the inductor ripple current charges or The APW 7179 provides internal over-temperature protection. When the junction temperature reaches 150 discharges the pure capacitor without the ESR. degrees centigrade, the APW7179 will turn off both internal power PMOSFET and NMOSFET. The estimation of the junction temperature, TJ, is defined as: ∆IL 0A I(COUT) TJ = PD ⋅ θJA ............................................(10 ) where the θJA is the thermal resistance of the package utilized by the APW7179. 0.5TS ∆VOUT1 Output Voltage Setting V OUT Then APW7179 has the adjustable version for output voltage setting by the users. A suggestion of maximum value of R2 is 300kΩ to keep the minimum current that provides Figure-3 Evaluate the ∆VOUT1 by the ideal of energy equalization. enough noise rejection ability through the resistor divider. The output voltage is programmed by the equation as According to the definition of Q, Q= below: 11 1 ∆IL ⋅ TS = COUT ⋅ ∆VOUT 1 ....( 6 ) 2 22 R VOUT = 0.6 ⋅ 1 + 1 ...............................(11) R 2 where TS is the inverse of switching frequency and the ∆IL VOUT is the inductor current ripple. Move the COUT to the left side to estimate the value of ∆VOUT1 as equation (7). ∆VOUT1 = ∆IL ⋅ TS ................................(7) 8 ⋅ COUT APW7179 R1 FB As mentioned above, one part of output voltage ripple is the product of the inductor current ripple and ESR of output capacitor. The equation (8) explains the output volt- R2 age ripple estimation. Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 10 www.anpec.com.tw APW7179 Application Information (Cont.) Layout Consideration For all switching power supplies, the layout is an important step in the design; especially at high peak currents and switching frequencies. If the layout is not carefully done, the regulator might show noise problems and duty cycle jitter. 1. The input capacitor should be placed close to the VIN and the GND. Connecting the capacitor and VIN/GND with short and wide trace without any via holes for good input voltage filtering. 2. The high current paths (GND1/GND2, IN1/IN2, and SW1/ SW2) should be placed very close to the device with short, direct and wide traces. 3. To minimize copper trace connections that can inject noise into the system, the inductor should be placed as close as possible to the SW pin to minimize the noise coupling into other circuits. 4. Since the feedback pin and network is a high impedance circuit, the feedback network should be routed away from the inductor. The feedback pin and feedback network should be shielded with a ground plane or trace to minimize noise coupling into this circuit. 5. A star ground connection or ground plane minimizes ground shifts and noise is recommended. Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 11 www.anpec.com.tw APW7179 Package Information TDFN3x3-12 D b E A Pin 1 A1 A3 D2 L K E2 Pin 1 Corner e S Y M B O L TDFN3x3-12 MILLIMETERS INCHES MIN. MAX. MIN. MAX. A 0.70 0.80 0.028 0.031 A1 0.00 0.05 0.000 0.002 0.012 A3 0.20 REF 0.008 REF b 0.18 0.30 0.007 D 2.90 3.10 0.114 0.122 D2 2.20 2.70 0.087 0.106 E 2.90 3.10 0.114 0.122 1.75 0.055 0.069 0.50 0.012 E2 1.40 e 0.45 BSC L 0.30 K 0.20 Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 0.018 BSC 0.020 0.008 12 www.anpec.com.tw APW7179 Carrier Tape & Reel Dimensions P0 P2 P1 A B0 W F E1 OD0 K0 A0 A OD1 B B T SECTION A-A SECTION B-B H A d T1 Application TDFN3x3-12 A H 330±2.00 50 MIN. P0 P1 T1 12.4+2.00 -0.00 P2 4.0±0.10 8.0±0.10 2.0±0.05 C 13.0+0.50 -0.20 D0 1.5+0.10 -0.00 d D W E1 F 1.5 MIN. 20.2 MIN. 12.0±0.30 1.75±0.10 5.5±0.05 D1 T 0.6+0.00 -0.40 A0 B0 K0 3.30±0.20 3.30±0.20 1.30±0.20 1.5 MIN. (mm) Devices Per Unit Package Type Unit Quantity TDFN3x3-12 Tape & Reel 3000 Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 13 www.anpec.com.tw APW7179 Taping Direction Information TDFN3x3-12 USER DIRECTION OF FEED Classification Profile Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 14 www.anpec.com.tw APW7179 Classification Reflow Profiles Profile Feature Sn-Pb Eutectic Assembly Pb-Free Assembly 100 °C 150 °C 60-120 seconds 150 °C 200 °C 60-120 seconds 3 °C/second max. 3°C/second max. 183 °C 60-150 seconds 217 °C 60-150 seconds See Classification Temp in table 1 See Classification Temp in table 2 Time (tP)** within 5°C of the specified classification temperature (Tc) 20** seconds 30** seconds Average ramp-down rate (Tp to Tsmax) 6 °C/second max. 6 °C/second max. 6 minutes max. 8 minutes max. Preheat & Soak Temperature min (Tsmin) Temperature max (Tsmax) Time (Tsmin to Tsmax) (ts) Average ramp-up rate (Tsmax to TP) Liquidous temperature (TL) Time at liquidous (tL) Peak package body Temperature (Tp)* Time 25°C to peak temperature * Tolerance for peak profile Temperature (Tp) is defined as a supplier minimum and a user maximum. ** Tolerance for time at peak profile temperature (tp) is defined as a supplier minimum and a user maximum. Table 1. SnPb Eutectic Process – Classification Temperatures (Tc) Package Thickness <2.5 mm ≥2.5 mm Volume mm <350 235 °C 220 °C 3 Volume mm ≥350 220 °C 220 °C 3 Table 2. Pb-free Process – Classification Temperatures (Tc) Package Thickness <1.6 mm 1.6 mm – 2.5 mm ≥2.5 mm Volume mm <350 260 °C 260 °C 250 °C 3 Volume mm 350-2000 260 °C 250 °C 245 °C 3 Volume mm >2000 260 °C 245 °C 245 °C 3 Reliability Test Program Test item SOLDERABILITY HOLT PCT TCT HBM MM Latch-Up Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 Method JESD-22, B102 JESD-22, A108 JESD-22, A102 JESD-22, A104 MIL-STD-883-3015.7 JESD-22, A115 JESD 78 15 Description 5 Sec, 245°C 1000 Hrs, Bias @ Tj=125°C 168 Hrs, 100%RH, 2atm, 121°C 500 Cycles, -65°C~150°C VHBM≧2KV VMM≧200V 10ms, 1tr≧100mA www.anpec.com.tw APW7179 Customer Service Anpec Electronics Corp. Head Office : No.6, Dusing 1st Road, SBIP, Hsin-Chu, Taiwan, R.O.C. Tel : 886-3-5642000 Fax : 886-3-5642050 Taipei Branch : 2F, No. 11, Lane 218, Sec 2 Jhongsing Rd., Sindian City, Taipei County 23146, Taiwan Tel : 886-2-2910-3838 Fax : 886-2-2917-3838 Copyright ANPEC Electronics Corp. Rev. A.1 - Mar., 2011 16 www.anpec.com.tw