® RT6150A/B Current Mode Buck-Boost Converter General Description Features The RT6150A/B is a high efficiency, fixed frequency, BuckBoost DC/DC converter that operates from input voltages above, below or equal to the output voltage. The topology incorporated in the IC provides a continuous transfer function through all operating modes, making the product ideal for single lithium-ion, multi-cell alkaline or Ni-MH battery applications where the output voltage is within the battery voltage range. Single Inductor Fixed Frequency Operation with Battery Voltages Synchronous Rectification : Up to 90% Efficiency Up to 800mA Continuous Output Current VOUT Disconnected from VIN during Shutdown Power Save Mode (PSM) Enable Control <1μ μA Shutdown Current Input Voltage Range: 1.8V to 5.5V Fixed 3.3V and Adjustable Output Voltage Options from 1.8V to 5.5V 10-Lead WDFN Packages RoHS Compliant and Halogen Free The device includes two N-MOSFET switches and two PMOSFET switches for high efficiency operation. Switching frequency is set at 1MHz to reduce the external component size. Quiescent current is only 60μA in Power Save Mode (PSM), maximizing battery life in portable applications. PSM operation is user controlled and can be enabled by driving the PS pin low. If the PS pin is driven high, then fixed frequency switching is enabled. Ordering Information RT6150A/BPackage Type QW : WDFN-10L 3x3 (W-Type) QW : WDFN-10L 2.5x2.5 (W-Type) Other features include low shutdown current, internal soft-start control, thermal shutdown protection and current limit. The RT6150A is available in the WDFN-10L 3x3 package and the RT6150B is available in the WDFN-10L 2.5x2.5 package. Lead Plating System G : Green (Halogen Free and Pb Free) Output Voltage 33 : 3.3V (Only for RT6150B) A : WDFN-10L 3x3 B : WDFN-10L 2.5x2.5 Applications Note : Portable Products Handheld Instrumentation Richtek products are : RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit LX1 LX2 RT6150A/B VOUT VIN Battery VOUT R1 VINA FB Enable R2 EN PS GND Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6150A/B-05 July 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT6150A/B Marking Information Pin Configurations RT6150AGQW 0N=YM DNN VOUT LX2 GND LX1 VIN YMDNN : Date Code 1 2 3 4 5 GND (TOP VIEW) 0N= : Product Code 11 10 9 8 7 6 FB GND VINA PS EN WDFN-10L 3x3 / WDFN-10L 2.5x2.5 RT6150BGQW 00 : Product Code W : Date Code 00W RT6150B-33GQW 03 : Product Code 03W W : Date Code Functional Pin Description Pin No. Pin Name Pin Function 1 VOUT Output of the Buck-Boost Converter. Connect a capacitor between the VOUT and GND. 2 LX2 Second Switch Node. Connect this pin to the inductor. 3, 9, 11 (Exposed Pad) GND Power Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 4 LX1 First Switch Node. Connect this pin to the inductor. 5 VIN Power Input. Connect an at least 10F capacitor between the VIN pin and GND. 6 EN Enable Control Input for the Buck-Boost Converter. 7 PS PSM Control Input. Pull low for PSM operation and pull high for fixed switching frequency operation. 8 VINA Supply Voltage Input for Control Circuit. 10 FB Feedback Input. For adjustable versions, connect a resistive divider to set the output voltage and it can be adjusted from 1.8V to 5.5V; For fixed version, must be connected to VOUT. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS6150A/B-05 July 2015 RT6150A/B Function Block Diagram LX2 LX1 VIN VOUT Gate Driver VINA ISENSE Temp Control OCP Zero Current OTP VPSM CTRL PS EN CMP OSC SS + AMP + - + Slop Comp VREF FB CC RC GND Operation The RT6150A/B is a synchronous average current mode switching Buck-Boost converter designed to maintain a fixed output voltage from an input supply that can be above, equal, or below the output voltage. The average inductor current is regulated by a fast current regulator which is controlled by a voltage control loop. The voltage error amplifier gets its feedback input from the FB pin. For adjustable output voltage, a resistive voltage divider must be connected to the FB pin. When VIN is greater than VOUT, the device operates in Buck mode. When VIN is lower than VOUT, the device operates in Boost mode. When VIN is close to VOUT, the RT6150A/B automatically enters Buck-Boost mode. In BuckBoost mode, the converter will maintain the regulation for output voltage and keep a minimum current ripple in the inductor to guarantee good performance. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6150A/B-05 July 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT6150A/B Absolute Maximum Ratings (Note 1) VOUT, VIN, EN, PS, VINA, FB Pin -----------------------------------------------------------------------------------Switch Output Voltage, LX1, LX2 Pin ---------------------------------------------------------------------------------< 10ns ------------------------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WDFN-10 3x3 --------------------------------------------------------------------------------------------------------------WDFN-10 2.5x2.5 ---------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WDFN-10 3x3, θJA ---------------------------------------------------------------------------------------------------------WDFN-10 3x3, θJC --------------------------------------------------------------------------------------------------------WDFN-10 2.5x2.5, θJA ----------------------------------------------------------------------------------------------------WDFN-10 2.5x2.5, θJC ---------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ----------------------------------------------------------------------------------------------MM (Machine Model) ------------------------------------------------------------------------------------------------------ Recommended Operating Conditions −0.3V to 6V −0.3V to 6V −2V to 7.5V 3.28W 2.44W 30.5°C/W 7.5°C/W 40.9°C/W 18.6°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VIN ------------------------------------------------------------------------------------------------ 1.8V to 5.5V Junction Temperature Range --------------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range --------------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = VOUT = 3.6V, TA = 25° C, unless otherwise specified.) Parameter Min Typ Max High-Level -- 1.65 1.8 Low-Level 1.4 1.55 -- 0.495 0.5 0.505 V -- 1 50 nA -- 60 -- -- 0.1 1 N-MOSFET Switch Leakage -- 0.1 5 A P-MOSFET Switch Leakage N-MOSFET Switch On Resistance P-MOSFET Switch On Resistance Switch Current Limit -- 0.1 10 A RDS(ON)_N -- 0.15 -- RDS(ON)_P -- 0.15 -- ILIM 1.6 -- -- A Oscillator Frequency fOSC 0.8 1 1.2 MHz -- 0.65 1 ms Input Voltage UVLO Feedback Voltage Symbol VFB Feedback Input Current VPS = VIN VFB = 0.5V IOUT = 0mA, PS = 0V (Note 5) Power Save Mode EN = 0V, Not Including Switch Leakage Shutdown Quiescent Current Soft-Start Time Test Conditions tSS VIN = 3.6V Time from when EN signal asserts to output voltage IOUT = 0mA Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 Unit V A is a registered trademark of Richtek Technology Corporation. DS6150A/B-05 July 2015 RT6150A/B Parameter EN and PS Input Voltage Symbol Min Typ Max Logic-High 1.2 -- -- Logic-Low -- -- 0.4 -- 0.01 1 A -- 140 -- C EN and PS Input Current Thermal Shutdown Test Conditions VEN = VPS = VIN TSD Unit V Note 1. Stresses beyond those listed “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2. θJA is measured at TA = 25°C on a high effective thermal conductivity four-layer test board per JEDEC 51-7. θJC is measured at the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. Current measurements are performed when the output are not switching. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6150A/B-05 July 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT6150A/B Typical Application Circuit RT6150A/B VIN 5 CIN 10µF 8 VIN VOUT 1 VINA FB Enable 6 7 EN LX2 R1 487k 10 LX1 4 VOUT R2 86.6k 2 PS COUT 20µF L 2.2µH GND 3, 9, 11 (Exposed Pad) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS6150A/B-05 July 2015 RT6150A/B Typical Operating Characteristics Buck-Boost 3.3V Efficiency Buck-Boost 3.3V Efficiency 100 100 90 90 80 VIN = 1.8V VIN = 2.4V VIN = 3.3V VIN = 4.2V VIN = 5.5V 70 60 50 Efficiency (%) Efficiency (%) 80 40 30 VIN = 1.8V VIN = 2.4V VIN = 3.3V VIN = 4.2V VIN = 5.5V 70 60 50 40 30 20 20 10 10 L = 2.2μH, COUT = 20μF, PS/SYNC = L L = 2.2μH, COUT = 20μF, PS/SYNC = H 0 0 1 10 100 1 1000 10 100 1000 Output Current (mA) Output Current (mA) Efficiency vs. Input Voltage Output Voltage vs. Output Current 100 3.6 90 3.5 Output Voltage (V) Efficiency (%) 80 IOUT = 500mA IOUT = 100mA IOUT = 10mA 70 60 50 40 30 20 3.4 3.3 VIN = 1.8V VIN = 2.4V VIN = 3.3V VIN = 4.2V VIN = 5V 3.2 3.1 10 L = 2.2μH, COUT = 20μF, PS/SYNC = L COUT = 20μF, PS = L 0 3.0 1.8 2.54 3.28 4.02 4.76 5.5 0 200 600 800 1000 Maximum Output Current vs. Input Voltage Output Voltage vs. Input Voltage 3.6 Maximum Output Current (mA)1 2000 3.5 Output Voltage (V) 400 Output Current (mA) Input Voltage (V) 3.4 3.3 IOUT = 500mA IOUT = 300mA IOUT = 100mA 3.2 3.1 1750 1500 1250 1000 750 500 250 COUT = 20μF, PS = L VOUT = 3.3V, COUT = 20μF, PS = H 0 3.0 1.8 2.54 3.28 4.02 4.76 Input Voltage (V) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6150A/B-05 July 2015 5.5 1.8 2.54 3.28 4.02 4.76 5.5 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT6150A/B Output Voltage Ripple Output Voltage Ripple LX1 (2V/Div) LX1 (2V/Div) LX2 (2V/Div) LX2 (2V/Div) VOUT_ac (20mV/Div) VOUT_ac (20mV/Div) VIN = 3.3V, VOUT = 3.3V, IOUT = 500mA, L = 2.2μH, COUT = 20μF VIN = 2.5V, VOUT = 3.3V, IOUT = 500mA, L = 2.2μH, COUT = 20μF Time (500ns/Div) Time (500ns/Div) Output Voltage Ripple Load Transient Response LX1 (2V/Div) I LOAD (200mA/Div) VOUT_ac (100mV/Div) LX2 (2V/Div) VOUT_ac (20mV/Div) VIN = 4.2V, VOUT = 3.3V, IOUT = 500mA, L = 2.2μH, COUT = 20μF VIN = 3V, VOUT = 3.3V, IOUT = 200mA to 600mA, L = 2.2μH, COUT = 20μF Time (500ns/Div) Time (2.5ms/Div) Load Transient Response Load Transient Response I LOAD (200mA/Div) VOUT_ac (100mV/Div) I LOAD (200mA/Div) VOUT_ac (100mV/Div) VIN = 3.3V, VOUT = 3.3V, IOUT = 200mA to 600mA, L = 2.2μH, COUT = 20μF Time (2.5ms/Div) Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 VIN = 4.2V, VOUT = 3.3V, IOUT = 200mA to 600mA, L = 2.2μH, COUT = 20μF Time (2.5ms/Div) is a registered trademark of Richtek Technology Corporation. DS6150A/B-05 July 2015 RT6150A/B Application Information The RT6150A/B Buck-Boost DC/DC converter is designed for systems powered by one-cell Li-Ion or Li-Polymer battery with a typical voltage between 2.5V and 4.2V. They can also be used in systems powered by a double or triple cell Alkaline, NiCd, or NiMH battery with a typical terminal voltage between 1.8V and 5.5V. Additionally, the output voltage can be set between 1.8V and 5.5V. The controller monitors the average input current as well as the peak input current. With this, maximum input power can be controlled to achieve a safe and stable operation. To protect the device from overheating, an internal temperature sensor is implemented. for R2 is 80kΩ to 500kΩ, and the value of R1 is depended on the needed output voltage. Output voltage can be calculated by equation as below : V R1 = R2 OUT 1 VFB For example, an output voltage of 3.3V is needed. It is recommended to use a 487kΩ resistor for R1. For better transient response performance, adding a feedforward capacitor in parallel with R1 is recommended. The value for the feedforward capacitor can be calculated using equation as below : Cff = [(487k/R1) x 20] −20 (pF) Enable Power Save Mode The device can be enabled or disenabled by the EN pin. When the EN pin is higher than the threshold of logichigh, the device starts operation with soft-start. Once the EN pin is set at low, the device will be shut down. In shutdown mode, the converter stops switching, internal control circuitry is turned off, and the load is disconnected from the input. This also means that the output voltage can drop below the input voltage during shutdown. The PS pin can be used to select different operation modes. To enable Power Save Mode (PSM), the PS pin must be set at low. The PSM is used to improve the efficiency at light load. If the power save mode is disabled by pulling high the PS pin, the converter will operate in PWM mode with fixed switching frequency. Soft-Start When the RT6150A/B is enabled, the output voltage will increase to its setting value within 1ms. During start-up period, the duty cycle and the peak current are limited to reduce high peak current flowing from the input. Output Voltage Setting There are fixed and adjustable output voltage versions available. To properly configure the fixed output voltage devices, the FB pin is used to sense the output voltage and must be connected directly to VOUT. At the adjustable versions, the output voltage is setting by an external resistive divider. The resistive divider must be connected between VOUT, FB and GND. When the output voltage is regulated properly, the typical value of the voltage at the FB pin is 500mV, and the current into FB pin is about 10nA generally. The current through divider resistor should be about 100 times larger than the current into FB pin in order to neglect the FB input current. The suggested value Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6150A/B-05 July 2015 Under-Voltage Lockout The under-voltage lockout circuit prevents the device from operating incorrectly at low input voltages. It prevents the converter from turning on the power switches under undefined conditions and prevents the battery from deep discharge. VINA voltage must be greater than 1.65V to enable the converter. During operation, if VINA voltage drops below 1.55V, the converter is disabled until the supply exceeds the UVLO rising threshold. The RT6150A/B automatically restarts if the input voltage recovers to the input voltage UVLO high level. Thermal Shutdown The device has a built-in temperature sensor which monitors the internal junction temperature. If the temperature exceeds the threshold, the device stops operating. As soon as the IC temperature has decreased below the threshold with a hysteresis, it starts operating again. The built-in hysteresis is designed to avoid unstable operation at IC temperatures near the over temperature threshold. is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT6150A/B Inductor Selection To properly configure the Buck-Boost converter, an inductor must be connected between the LX1 and LX2 pins. To estimate the inductance value, two equations are listed as below : L1 > VOUT VIN(MAX) VOUT f IL VIN(MAX) L2 > VIN(MIN) VOUT VIN(MIN) f IL VOUT (H) (H) where f is the minimum switching frequency. L1 is the minimum inductor value for Buck mode operation. VIN(MAX) is the maximum input voltage. L2 is the minimum inductance, for Boost mode operation. VIN(MIN) is the minimum input voltage. The recommended minimum inductor value is either L1 or L2 whichever is higher. For example, a suitable inductor value is 2.2μH for generating a 3.3V output voltage from a Li-Ion battery with the range from 2.5V to 4.2V. The recommended inductor value range is between 1.5μH and 4.7μH. In general, a higher inductor value offers better performance in high voltage conversion condition. Input Capacitor Selection At least a 10μF input capacitor is recommended to improve transient behavior of the regulator and EMI behavior of the total power supply circuit. A ceramic capacitor placed as close as possible to the VIN and GND pins of the IC is recommended. Output Capacitor Selection The output capacitor selection determines the output voltage ripple and transient response. It is recommended to use ceramic capacitors placed as close as possible to the VOUT and GND pins of the IC. If, for any reason, the application requires the use of large capacitors which can not be placed close to the IC, using a small ceramic capacitor in parallel to the large one is recommended. This small capacitor should be placed as close as possible to the VOUT and GND pins of the IC. The output voltage ripple for a given output capacitor is expressed as follows : VOUT , peak (Buck) = VOUT (VIN VOUT ) VIN 8 L (fOSC )2 COUT I (VOUT VIN ) VOUT , peak (Boost) = LOAD COUT VOUT fOSC Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 If the RT6150A/B operates in Buck mode, the worst-case voltage ripple occurs at the highest input voltage. When the RT6150A/B operates in boost mode, the worst-case voltage ripple occurs at the lowest input voltage. The maximum voltage of overshoot or undershoot, is inversely proportional to the value of the output capacitor. To ensure stability and excellent transient response, it is recommended to use a minimum of 10μF/X7R/1206 capacitors at the output. For surface mount applications, Taiyo Yuden or TDK ceramic capacitors, X7R series Multilayer Ceramic Capacitor is recommended. A capacitor with a value in the range of the calculated minimum should be used. This is required to maintain control loop stability. There are no additional requirements regarding minimum ESR. Low ESR capacitors should be used to minimize output voltage ripple. Larger capacitors will cause lower output voltage ripple as well as lower output voltage drop during load transients. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WDFN-10L 3x3 package, the thermal resistance, θJA, is 30.5°C/W on a standard JEDEC 51-7 four-layer thermal test board. For WDFN-10L 2.5x2.5 package, the thermal resistance, θJA, is 40.9°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : is a registered trademark of Richtek Technology Corporation. DS6150A/B-05 July 2015 RT6150A/B PD(MAX) = (125°C − 25°C) / (30.5°C/W) = 3.28W for WDFN-10L 3x3 package Layout Considerations For the best performance of the RT6150A/B, the following PCB layout guidelines must be strictly followed. PD(MAX) = (125°C − 25°C) / (40.9°C/W) = 2.44W for WDFN-10L 2.5x2.5 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Maximum Power Dissipation (W)1 3.5 Place the input and output capacitors as close as possible to the input and output pins respectively for good filtering. Keep the main power traces as wide and short as possible. The switching node area connected to LX and inductor should be minimized for lower EMI. Place the feedback components as close as possible to the FB pin and keep these components away from the noisy devices. Connect the GND and Exposed Pad to a strong ground plane for maximum thermal dissipation and noise protection. Directly connect the output capacitors to the feedback network to avoid bouncing caused by parasitic resistance and inductance from the PCB trace. Four-Layer PCB WDFN-10L 3x3 3.0 2.5 2.0 WDFN-10L 2.5x2.5 1.5 1.0 0.5 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 1. Derating Curve of Maximum Power Dissipation VOUT GND R1 Input/Output capacitors must be placed as close as possible to the Input/Output pin. L VOUT 1 LX2 GND 2 LX1 VIN 4 3 5 GND COUT 10 FB 9 GND VINA 8 7 11 6 R2 VIN The feedback divider should be placed as close as possible to the FB pin. PS EN CIN GND LX should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. Figure 2. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS6150A/B-05 July 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT6150A/B Outline Dimension D2 D L E E2 1 e SEE DETAIL A b 2 1 2 1 A A1 A3 DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 2.950 3.050 0.116 0.120 D2 2.300 2.650 0.091 0.104 E 2.950 3.050 0.116 0.120 E2 1.500 1.750 0.059 0.069 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 10L DFN 3x3 Package Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS6150A/B-05 July 2015 RT6150A/B 2 1 2 1 DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Symbol Dimensions In Millimeters Dimensions In Inches Min. Max. Min. Max. A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.200 0.300 0.008 0.012 D 2.400 2.600 0.094 0.102 D2 1.950 2.050 0.077 0.081 E 2.400 2.600 0.094 0.102 E2 1.150 1.250 0.045 0.049 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 10L DFN 2.5x2.5 Package Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st Street, Chupei City Hsinchu, Taiwan, R.O.C. Tel: (8863)5526789 Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries. DS6150A/B-05 July 2015 www.richtek.com 13