RT8020E Dual High-Efficiency PWM Step-Down DC/DC Converter General Description Features The RT8020E is a dual high-efficiency Pulse-WidthModulated (PWM) step-down DC/DC converter. It is capable of delivering 1A output current over a wide input voltage range from 2.5V to 5.5V. The RT8020E is ideally suited for portable electronic devices that are powered by 1-cell Li-ion battery or other power sources within the range such as cellular phones, PDAs and other hand-held devices. z 2.5V to 5.5V Input Range z 1.2V and 1.8V Fixed Output Voltage 1A Output Current 95% Efficiency No Schottky Diode Required 50μ μA Quiescent Current per Channel 1.5MHz Fixed Frequency PWM Operation Small 12-Lead WDFN Package RoHS Compliant and Halogen Free Two operational modes are available : PWM/Low-Dropout auto-switch mode and shutdown mode. Internal synchronous rectifier with low R DS(ON) dramatically reduces conduction loss at PWM mode. No external Schottky diode is required in practical application. The RT8020E enters Low-Dropout mode when normal PWM cannot provide regulated output voltage by continuously turning on the upper PMOS. The RT8020E enters shutdown mode and consumes less than 0.1μA when the EN pin is pulled low. The switching ripple is easily smoothed-out by small package filtering elements due to a fixed operation frequency of 1.5MHz. This, along with a small WDFN-12L 3x3 package, provides an ideal solution for small PCB area application. Other features include soft start, lower internal reference voltage with 2% accuracy, over temperature protection, and over current protection. z z z z z z z Applications z z z z z z Digital Still Cameras Mobile Phones Personal Information Appliances Wireless and DSL Modems MP3 Players Portable Instruments Ordering Information RT8020E Package Type QW : WDFN-12L 3x3 (W-Type) Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) Fixed Output Voltage : VOUT1/VOUT2 1.2V/1.8V Note : Richtek products are : Pin Configurations (TOP VIEW) VIN2 LX2 GND FB1 NC1 EN1 1 2 3 4 5 6 GND 13 12 11 10 9 8 7 EN2 NC2 FB2 GND LX1 VIN1 ` RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. WDFN-12L 3x3 Marking Information JS= : Product Code JS=YM DNN YMDNN : Date code DS8020E-02 March 2011 www.richtek.com 1 RT8020E Typical Application Circuit L2 4.7µH VIN2 VOUT2 1.8V RT8020E CIN2 4.7µF 1 VIN2 EN2 12 2 NC2 11 3, 13 (Exposed Pad) 4 LX2 COUT2 10µF FB2 10 GND FB1 GND 5 NC1 LX1 6 EN1 VIN1 9 8 7 CIN1 4.7µF VIN1 L1 4.7µH VOUT1 1.2V COUT1 10µF Functional Pin Description Pin No. Pin Name 1 VIN2 2 LX2 3, 9, 13 (Exposed Pad) 4 GND Pin Function Power Input of Channel 2. Pin for Switching of Channel 2. Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. FB1 Feedback of Channel 1. NC1, NC2 No Internal Connection or Connect to VIN. 6 EN1 Chip Enable of Channel 1 (Active High). VEN1 ≦ VIN1. 7 VIN1 Power Input of Channel 1. 5, 11 8 LX1 Pin for Switching of Channel 1. 10 FB2 Feedback of Channel 2. 12 EN2 Chip Enable of Channel 2 (Active High). VEN2 ≦ VIN2. www.richtek.com 2 DS8020E-02 March 2011 RT8020E Function Block Diagram ENx VINx RS1 OSC and Shutdown Control Current Limit Detector Slope Compensation Current Sense PWM Comparator FBx Driver LXx Error Amplifier RC COMP DS8020E-02 March 2011 Control Logic UVLO and Power Good Detector RS2 VREF GND www.richtek.com 3 RT8020E Absolute Maximum Ratings z z z z z z z z (Note 1) Supply Input Voltage, VIN1, VIN2 ----------------------------------------------------------------------------------- −0.3V to 6.5V EN1, FB1, LX1, EN2, FB2 and LX2 Pin Voltage --------------------------------------------------------------- −0.3V to VIN + 0.3V Power Dissipation, PD @ TA = 25°C WDFN-12L 3x3 --------------------------------------------------------------------------------------------------------- 1.667W Package Thermal Resistance (Note 2) WDFN-12L 3x3, θJA --------------------------------------------------------------------------------------------------- 60°C/W WDFN-12L 3x3, θJC --------------------------------------------------------------------------------------------------- 8.2°C/W Lead Temperature (Soldering, 10 sec.) --------------------------------------------------------------------------- 260°C Junction Temperature ------------------------------------------------------------------------------------------------- 150°C Storage Temperature Range ---------------------------------------------------------------------------------------- −65°C to 150°C ESD Susceptibility (Note 3) HBM (Human Body Mode) ------------------------------------------------------------------------------------------ 2kV MM (Machine Mode) -------------------------------------------------------------------------------------------------- 200V Recommended Operating Conditions z z z (Note 4) Supply Input Voltage, VIN1, VIN2 ----------------------------------------------------------------------------------- 2.5V to 5.5V Junction Temperature Range ---------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ---------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 3.6V, VOUT = 1.8V, L = 4.7μH, CIN = 4.7μF, COUT = 10μF, IMAX= 1A, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit -- 1.8 -- V -- 0.1 -- V Channel 1 and Channel 2 Under Voltage Lock Out threshold VUVLO Hysteresis Quiescent Current IQ IOUT = 0mA, VFB = VREF + 5% -- 50 70 μA Shutdown Current I SHDN EN = GND -- 0.1 1 μA ΔVOUT1 VIN1 = 2.5V to 5.5V, VOUT1 = 1.2V 0A < IOUT1 < 1A −2 -- 2 % ΔVOUT2 −2 -- 2 % −50 -- 50 nA VIN = 2.5V -- 0.38 -- VIN = 3.6V -- 0.28 -- VIN = 2.5V -- 0.35 -- VIN = 3.6V -- 0.25 -- Output Voltage Accuracy FB Input Current I FB VIN2 = 2.5 to 5.5V, VOUT2 = 1.8V 0A < IOUT2 < 1A VFB = VIN RDS(ON) of P-MOSFET RDS(ON)_P IOUT = 200mA RDS(ON) of N-MOSFET RDS(ON)_N IOUT = 200mA P-Channel Current Limit I LIM_P VIN = 2.5V to 5.5 V 1.4 1.5 2 Logic-High EN Input Threshold Voltage Logic-Low VIH VIN = 2.5V to 5.5V 1.5 -- VIN VIL VIN = 2.5V to 5.5V -- -- 0.4 Oscillator Frequency f OSC VIN = 3.6V, IOUT = 100mA 1.2 1.5 1.8 Ω Ω A V MHz To be continued www.richtek.com 4 DS8020E-02 March 2011 RT8020E Parameter Symbol Thermal Shutdown Temperature TSD Maximum Duty Cycle DMAX LX Leakage Current ILX Test Conditions VIN = 3.6V, VLX = 0V or VLX = 3.6V Min Typ Max Unit -- 160 -- °C 100 -- -- % −1 -- 1 μA Note 1. Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability. Note 2. θJA is measured in natural convection at TA = 25°C on a high effective thermal conductivity four-layer test board of JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on the exposed pad of the package. Note 3. Devices are ESD sensitive. Handling precaution recommended. Note 4. The device is not guaranteed to function outside its operating conditions. DS8020E-02 March 2011 www.richtek.com 5 RT8020E Typical Operating Characteristics CH1 Efficiency vs. Output Current CH2 Efficiency vs. Output Current 100 100 90 90 80 VIN VIN VIN VIN VIN VIN VIN VIN 70 60 50 40 30 = = = = = = = = 2.4V 2.7V 3V 3.3V 3.6V 3.9V 4.2V 4.5V Efficiency (%) Efficiency (%) 80 20 VIN VIN VIN VIN VIN VIN VIN VIN 70 60 50 40 30 = = = = = = = = 2.4V 2.7V 3V 3.3V 3.6V 3.9V 4.2V 4.5V 20 10 10 VOUT = 1.2V, L = 4.7μH, COUT = 10μF 0 0 0.2 0.4 0.6 0.8 VOUT = 1.8V, L = 4.7μH, COUT = 10μF 0 1 0 0.2 0.4 Output Current (A) 1 1.86 VIN VIN VIN VIN 1.21 = = = = 1.84 3V 3.6V 4.2V 5V Output Voltage (V) 1.22 Output Voltage (V) 0.8 CH2 Output Voltage vs. Output Current CH1 Output Voltage vs. Output Current 1.23 1.20 1.19 1.82 1.80 VIN VIN VIN VIN 1.78 VOUT = 1.2V, L = 4.7μH, COUT = 10μF = = = = 3V 3.6V 4.2V 5V VOUT = 1.8V, L = 4.7μH, COUT = 10μF 1.18 1.76 0 0.2 0.4 0.6 0.8 0 1 0.2 Output Current (A) 0.4 0.6 0.8 1 Output Current (A) CH2 Output Voltage vs. Input Voltage CH1 Output Voltage vs. Input Voltage 1.83 1.23 1.22 1.82 IOUT = 0mA IOUT = 300mA IOUT = 600mA 1.21 Output Voltage (V) Output Voltage (V) 0.6 Output Current (A) 1.20 IOUT = 0mA IOUT = 300mA IOUT = 600mA 1.81 1.80 1.79 1.19 VOUT = 1.8V, L = 4.7μH, COUT = 10μF VOUT = 1.2V, L = 4.7μH, COUT = 10μF 1.18 1.78 2.5 3.0 3.5 4.0 Input Voltage (V) www.richtek.com 6 4.5 5.0 2.5 3.0 3.5 4.0 4.5 5.0 Input Voltage (V) DS8020E-02 March 2011 RT8020E EN Pin Threshold vs. Temperature 2.0 1.8 1.8 1.6 1.6 EN Pin Threshold (V) EN Pin Threshold (V) EN Pin Threshold vs. Input Voltage 2.0 1.4 1.2 Rising 1.0 0.8 Falling 0.6 0.4 VOUT = 1.2V, L = 4.7μH, COUT = 10μF, IOUT = 0A 0.2 1.4 1.2 Rising 1.0 0.8 Falling 0.6 0.4 VOUT = 1.2V, L = 4.7μH, COUT = 10μF, IOUT = 0A 0.2 0.0 0.0 2.5 3.0 3.5 4.0 4.5 5.0 -50 5.5 -25 0 Switching Frequency vs. Input Voltage 75 100 125 Switching Frequency vs. Temperature 1600 Switching Frequency (kHz)1 1600 Switching Frequency (kHz)1 50 Temperature (°C) Input Voltage (V) 1550 1500 1450 1400 1350 VOUT = 1.8V, L = 4.7μH, COUT = 10μF, IOUT = 300mA 1550 1500 1450 1400 1350 VIN = 3.7V, VOUT = 1.8V, L = 4.7μH, COUT = 10μF, IOUT = 300mA 1300 1300 2.5 3 3.5 4 4.5 -50 5 -25 0 1.83 1.21 1.82 Output Voltage (V) 1.20 1.19 VIN = 2.5V VIN = 3.7V VIN = 4.5V 1.17 1.16 VOUT = 1.2V, L = 4.7μH, COUT = 10μF, IOUT = 300mA 1.15 50 75 100 125 CH2 Output Voltage vs. Temperature CH1 Output Voltage vs. Temperature 1.22 1.18 25 Temperature (°C) Input Voltage (V) Output Voltage (V) 25 1.81 1.80 1.79 VIN = 2.5V VIN = 3.7V VIN = 4.5V 1.78 1.77 1.76 VOUT = 1.8V, L = 4.7μH, COUT = 10μF, IOUT = 300mA 1.75 1.74 1.14 -50 -25 0 25 50 Temperature (°C) DS8020E-02 March 2011 75 100 125 -50 -25 0 25 50 75 100 125 Temperature (°C) www.richtek.com 7 RT8020E Output Current Limit vs. Temperature Output Current Limit vs. Input Voltage 2.4 2.6 VOUT = 1.2V, L = 4.7μH, COUT = 10μF Output Current Limit (A) Output Current Limit (A) VOUT = 1.2V, L = 4.7μH, COUT = 10μF 2.4 2.2 2.0 1.8 1.6 1.4 1.2 2.2 VIN = 5V 2.0 VIN = 3.6V 1.8 1.6 1.4 VIN = 2.5V 1.2 1.0 1.0 2.5 3.0 3.5 4.0 4.5 -50 5.0 0 25 50 75 Input Voltage (V) Temperature (°C) CH1 Power On from EN CH1 Power Off from EN I IN (500mA/Div) I IN (500mA/Div) VEN (2V/Div) VEN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) Time (100μs/Div) Time (100μs/Div) CH1 Power On from EN CH1 Power Off from EN VIN = 3.6V, VOUT = 1.2V, IOUT = 1A I IN (1A/Div) 100 125 VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA VIN = 3.6V, VOUT = 1.2V, IOUT = 1A I IN (1A/Div) VEN (2V/Div) VEN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) Time (500μs/Div) www.richtek.com 8 -25 Time (500μs/Div) DS8020E-02 March 2011 RT8020E CH2 Power On from EN CH2 Power Off from EN VIN = 3.6V, VOUT = 1.8V, IOUT = 10mA VIN = 3.6V, VOUT = 1.8V, IOUT = 10mA I IN (500mA/Div) I IN (500mA/Div) VEN (2V/Div) VEN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) Time (100μs/Div) Time (100μs/Div) CH2 Power On from EN CH2 Power Off from EN VIN = 3.6V, VOUT = 1.8V, IOUT = 1A VIN = 3.6V, VOUT = 1.8V, IOUT = 1A I IN (1A/Div) I IN (1A/Div) VEN (2V/Div) VEN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) Time (500μs/Div) Time (500μs/Div) Power On from VIN Power Off from VIN VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA I IN (500mA/Div) I IN (500mA/Div) VIN (2V/Div) VIN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) Time (250μs/Div) DS8020E-02 March 2011 Time (1ms/Div) www.richtek.com 9 RT8020E Output Voltage Ripple Output Voltage Ripple VIN = 3.6V, VOUT = 1.2V, IOUT = 1A VIN = 5V, VOUT = 1.2V, IOUT = 1A VLX (2V/Div) VLX (2V/Div) VOUT (5mV/Div) VOUT (5mV/Div) Time (500ns/Div) Time (500ns/Div) Load Transient Response Load Transient Response VIN = 3.6V, VOUT = 1.2V, IOUT = 50mA to 500mA VIN = 3.6V, VOUT = 1.2V, IOUT = 50mA to 1A IOUT (500mA/Div) IOUT (500mA/Div) VOUT (20mV/Div) VOUT (20mV/Div) Time (1ms/Div) Time (1ms/Div) Load Transient Response Load Transient Response VIN = 5V, VOUT = 1.2V, IOUT = 50mA to 1A VIN = 5V, VOUT = 1.2V, IOUT = 50mA to 500mA IOUT (500mA/Div) IOUT (500mA/Div) VOUT (20mV/Div) VOUT (20mV/Div) Time (1ms/Div) www.richtek.com 10 Time (1ms/Div) DS8020E-02 March 2011 RT8020E Applications Information The basic RT8020E application circuit is shown in Typical Application Circuit. External component selection is determined by the maximum load current and begins with the selection of the inductor value and operating frequency followed by CIN and COUT. Inductor Selection For a given input and output voltage, the inductor value and operating frequency determine the ripple current. The ripple current ΔIL increases with higher VIN and decreases with higher inductance. ⎡V ⎤ ⎡ V ⎤ ΔIL = ⎢ OUT ⎥ × ⎢1 − OUT ⎥ f L × V IN ⎦ ⎣ ⎦ ⎣ Having a lower ripple current reduces the ESR losses in the output capacitors and the output voltage ripple. Highest efficiency operation is achieved at low frequency with small ripple current. This, however, requires a large inductor. A reasonable starting point for selecting the ripple current is ΔIL = 0.4(IMAX). The largest ripple current occurs at the highest VIN. To guarantee that the ripple current stays below a specified maximum, the inductor value should be chosen according to the following equation : ⎡ VOUT ⎤ ⎡ VOUT ⎤ L=⎢ ⎥ ⎥ × ⎢1 − V f I × Δ L(MAX) ⎦ ⎣ IN(MAX) ⎦ ⎣ Inductor Core Selection Once the value for L is known, the type of inductor can be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, thus, limiting the use to more expensive ferrite or permalloy cores. Actual core loss is independent of core size for a fixed inductor value, but it is very dependent on the inductance selected. As the inductance increases, core losses decrease. However, increased inductance requires more turns of wire and therefore higher copper losses. Ferrite designs have very low core losses and are preferred at high switching frequencies, thus allowing design goals to concentrate on copper loss and saturation prevention. Ferrite core material saturates “hard”, which means that inductance collapses abruptly when the peak design current is exceeded. DS8020E-02 March 2011 This results in an abrupt increase in inductor ripple current and consequent output voltage ripple. Do not allow the core to saturate! Different core materials and shapes will change the size/ current and price/current relationship of an inductor. Toroid or shielded pot cores in ferrite or permalloy materials are small and don't radiate energy but generally cost more than powdered iron core inductors with similar characteristics. The choice of which type of inductor to use mainly depends on the price vs. size requirements and any radiated field/EMI requirements. CIN and COUT Selection The input capacitance, C IN, is needed to filter the trapezoidal current at the source of the top MOSFET. To prevent large ripple voltage, a low ESR input capacitor sized for the maximum RMS current should be used. RMS current is given by : IRMS = IOUT(MAX) VOUT VIN VIN −1 VOUT This formula has a maximum at VIN = 2VOUT, where I RMS = I OUT/2. This simple worst-case condition is commonly used for design because even significant deviations do not result in much difference. Note that ripple current ratings from capacitor manufacturers are often based on a life time of only 2000 hours, which makes it advisable to further de-rate the capacitor or choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet the size or height requirements in the design. The selection of COUT is determined by the effective series resistance (ESR) that is required to minimize voltage ripple and load step transients, as well as by the amount of bulk capacitance that is necessary to ensure that the control loop is stable. Loop stability can be checked by viewing the load transient response as described in a later section. The output ripple, ΔVOUT, is determined by : ⎡ 1 ⎤ ΔVOUT ≤ ΔIL ⎢ESR + ⎥ 8fC OUT ⎦ ⎣ www.richtek.com 11 RT8020E The output ripple is highest at maximum input voltage since ΔIL increases with input voltage. Multiple capacitors placed in parallel may be needed to meet the ESR and RMS current handling requirements. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. Special polymer capacitors offer very low ESR, but have lower capacitance density than other types. Tantalum capacitors have the highest capacitance density, but it is important to only use types that have been surge tested for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR, but can be used in cost-sensitive applications provided that consideration is given to ripple current ratings and long-term reliability. Ceramic capacitors have excellent low ESR characteristics, but can have a high voltage coefficient and audible piezoelectric effects. The high Q of ceramic capacitors with trace inductance can also lead to significant ringing. Using Ceramic Input and Output Capacitors Higher value, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. However, care must be taken when these capacitors are used at the input and output. When a ceramic capacitor is used at the input and the power is supplied by a wall adapter through long wires, a load step at the output can induce ringing at the input, VIN. At best, this ringing can couple to the output and be mistaken as loop instability. At worst, a sudden inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. Efficiency Considerations The efficiency of a switching regulator is equal to the output power divided by the input power times 100%. It is often useful to analyze individual losses to determine what is limiting the efficiency and which change would produce the most improvement. Efficiency can be expressed as : Efficiency = 100% − (L1+ L2+ L3+...) where L1, L2, etc. are the individual losses as a percentage of input power. Although all dissipative elements in the circuit produce losses, two main sources usually account www.richtek.com 12 for most of the losses : VIN quiescent current and I2R losses. The VIN quiescent current loss dominates the efficiency loss at very low load currents whereas the I2R loss dominates the efficiency loss at medium to high load currents. In a typical efficiency plot, the efficiency curve at very low load currents can be misleading since the actual power lost is of no consequence. 1.The V IN quiescent current appears due to two components : the DC bias current and the gate charge currents. The gate charge current results from switching the gate capacitance of the internal power MOSFET switches. Each time the gate is switched from high to low to high again, a packet of charge ΔQ moves from VIN to ground. The resulting ΔQ/Δt is the current out of VIN that is typically larger than the DC bias current. In continuous mode, IGATECHG = f(QT + QB) where QT and QB are the gate charges of the internal top and bottom switches. Both the DC bias and gate charge losses are proportional to VIN and thus their effects will be more pronounced at higher supply voltages. 2. I2R losses are calculated from the resistances of the internal switches, RSW and external inductor, RL. In continuous mode the average output current flowing through inductor L is “chopped” between the main switch and the synchronous switch. Thus, the series resistance looking into the LX pin is a function of both top and bottom MOSFET RDS(ON) as well as the duty cycle (DC). The equation is shown below : RSW = RDS(ON)TOP x DC + RDS(ON)BOT x (1 − DC) The RDS(ON) for both the top and bottom MOSFETs can be obtained from the Typical Performance Characteristics curves. Thus, to obtain I2R losses, simply add RSW to RL and multiply the result by the square of the average output current. Other losses including C IN and C OUT ESR dissipative losses and inductor core losses generally account for less than 2% of the total loss. Checking Transient Response The regulator loop response can be checked by looking at the load transient response. Switching regulators take DS8020E-02 March 2011 RT8020E several cycles to respond to a step in load current. When a load step occurs, VOUT immediately shifts by an amount equal to ΔILOAD (ESR), where ESR is the effective series resistance of COUT. ΔILOAD also begins to charge or discharge COUT, generating a feedback error signal used by the regulator to return VOUT to its steady-state value. During this recovery time, VOUT can be monitored for overshoot or ringing which would indicate a stability problem. Maximum Power Dissipation (W) 1.8 Thermal Considerations 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 conditions specification of the RT8020E DC/DC converter, TJ(MAX) is the maximum junction temperature of the die and TA is the ambient temperature. The junction to ambient thermal resistance θJA is layout dependent. For WDFN12L 3x3 packages, the thermal resistance, θJA , is 60°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 : PD(MAX) = (125°C − 25°C) / (60°C/W) = 1.667W for WDFN-12L 3x3 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. For the RT8020E package, the derating curves in Figure 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. DS8020E-02 March 2011 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 The maximum power dissipation depends on the thermal resistance of 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 1.6 25 50 75 100 125 Ambient Temperature (°C) Figure 1. Derating Curve for RT8020E Package Layout Considerations Follow the PCB layout guidelines for optimal performance of the RT8020E. ` For the main current paths, keep their traces short and wide. ` Place the input capacitor as close as possible to the device pins (VIN and GND). ` LX node experiences high frequency voltage swing and should be kept in a small area. Keep analog components away from LX node to prevent stray capacitive noise pick-up. ` Connect feedback network behind the output capacitors. Keep the loop area small. Place the feedback components near the RT8020E. ` Connect all analog grounds to a command node and then connect the command node to the power ground behind the output capacitors. www.richtek.com 13 RT8020E Outline Dimension 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 0.150 0.250 0.006 0.010 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 1.400 1.750 0.055 0.069 e L 0.450 0.350 0.018 0.450 0.014 0.018 W-Type 12L DFN 3x3 Package Richtek Technology Corporation Richtek Technology Corporation Headquarter Taipei Office (Marketing) 5F, No. 20, Taiyuen Street, Chupei City 5F, No. 95, Minchiuan Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)86672399 Fax: (8862)86672377 Email: [email protected] Information that is provided by Richtek Technology Corporation is believed to be accurate and reliable. Richtek reserves the right to make any change in circuit design, specification or other related things if necessary without notice at any time. No third party intellectual property infringement of the applications should be guaranteed by users when integrating Richtek products into any application. No legal responsibility for any said applications is assumed by Richtek. www.richtek.com 14 DS8020E-02 March 2011