RT8020GQW

® RT8020 Dual High-Efficiency PWM Step-Down DC/DC Converter General Description Features The RT8020 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 RT8020 is ideally suited for portable electronic devices that are powered from 1-cell Li-ion battery or from other power sources within the range such as cellular phones, PDAs and other handheld devices.  2.5V to 5.5V Input Range  Adjustable Output From 0.6V to VIN 1.2V, 1.3V, 1.8V, 2.5V and 3.3V Fixed/ Adjustable Output Voltage 1A Output Current 95% Efficiency No Schottky Diode Required 50uA Quiescent Current per Channel 1.5MHz Fixed Frequency PWM Operation Small 12-Lead WDFN Package RoHS Compliant and 100% Lead (Pb)-Free Two operational modes are available : PWM/Low-Dropout auto-switch and shutdown modes. Internal synchronous rectifier with low RDS(ON) dramatically reduces conduction loss at PWM mode. No external Schottky diode is required in practical application. The RT8020 enters Low-Dropout mode when normal PWM cannot provide regulated output voltage by continuously turning on the upper PMOS. The RT8020 enter shutdown mode and consumes less than 0.1μA when 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 small WDFN-12L 3x3 package provides small PCB area application. Other features include soft start, lower internal reference voltage with 2% accuracy, over temperature protection, and over current protection.         Applications      Mobile Phones Personal Information Appliances Wireless and DSL Modems MP3 Players Portable Instruments Ordering Information RT8020 Package Type QW : WDFN-12L 3x3 (W-Type) (Exposed Pad-Option 1) Lead Plating System P : Pb Free G : Green (Halogen Free and Pb Free) Output Voltage : VOUT1/VOUT2 Default : Adjustable A : 3.3V/1.8V B : 3.3V/1.3V C : 3.3V/1.2V D : 2.5V/1.8V 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 WDFN-12L 3x3 Note : Richtek products are :  RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020.  Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8020-07 August 2014 Suitable for use in SnPb or Pb-free soldering processes. is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8020 Marking Information RT8020APQW RT8020CPQW C2- : Product Code C2-YM DNN C4- : Product Code YMDNN : Date Code YMDNN : Date Code C4-YM DNN RT8020AGQW RT8020CGQW C2= : Product Code C2=YM DNN C4= : Product Code YMDNN : Date Code YMDNN : Date Code C4=YM DNN RT8020BPQW RT8020DPQW C3- : Product Code C3-YM DNN C5- : Product Code YMDNN : Date Code YMDNN : Date Code C5-YM DNN RT8020BGQW RT8020DGQW C3= : Product Code C3=YM DNN C5=: Product Code YMDNN : Date Code YMDNN : Date Code C5=YM DNN Typical Application Circuit COUT2 4.7µF L2 2.2µH VIN2 RT8020 CIN2 4.7µF C11 22pF 1 VIN2 EN2 12 2 LX2 NC2 11 GND FB2 10 3, Exposed Pad (13) R12 4 R11 850k FB1 GND 5 NC1 LX1 6 EN1 VIN1   R21 850k C21 22pF 9 8 7 R22 CIN1 4.7µF VIN1 L1 2.2µH VOUT1 VOUTx  VREF  1  Rx1 Rx2 VOUT2 COUT1 4.7µF Figure 1. Adjustable Voltage Regulator Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8020-07 August 2014 RT8020 L2 2.2µH VOUT2 VIN2 RT8020 CIN2 4.7µF 1 VIN2 EN2 12 2 NC2 11 3, Exposed Pad (13) 4 LX2 COUT2 4.7µF FB2 10 GND FB1 GND 5 NC1 LX1 6 EN1 VIN1 9 8 CIN1 4.7µF 7 VIN1 L1 2.2µH VOUT1 COUT1 4.7µF VOUTx = 1.2V, 1.3V, 1.8V, 2.5V or 3.3V Figure 2. Fixed Voltage Regulator Functional Pin Description Pin No. Pin Name Pin Function 1 VIN2 Power Input of Channel 2. 2 LX2 Pin for Switching of Channel 2. 3, 9, Exposed Pad (13) 4 GND 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 Connection or Connect to VIN. 6 EN1 Chip Enable of Channel 1 (Active High). VEN1 ≦ VIN1. 7 VIN1 Power Input of Channel 1. 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. 5, 11 Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8020-07 August 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8020 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 UVLO and Power Good Detector COMP Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 Control Logic RS2 V REF GND is a registered trademark of Richtek Technology Corporation. DS8020-07 August 2014 RT8020 Absolute Maximum Ratings         (Note 1) Supply Input Voltage, VIN1, VIN2 ---------------------------------------------------------------------------------EN1, FB1, LX1, EN2, FB2 and LX2 Pin Voltage -------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WDFN-12L 3x3 -------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WDFN-12L 3x3, θJA -------------------------------------------------------------------------------------------------WDFN-12L 3x3, θJC -------------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------------Junction Temperature -----------------------------------------------------------------------------------------------Storage Temperature Range --------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Mode) ----------------------------------------------------------------------------------------MM (Machine Mode) ------------------------------------------------------------------------------------------------- Recommended Operating Conditions    −0.3V to 6.5V −0.3V to (VIN + 0.3V) 1.667W 60°C/W 8.2°C/W 260°C 150°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage ------------------------------------------------------------------------------------------------- 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 = 2.5V, VREF = 0.6V, L = 2.2uH, CIN = 4.7μF, COUT = 10μF, TA = 25°C, IMAX= 1A unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit 2.5 -- 5.5 V -- 1.8 -- V -- 0.1 -- V Channel 1 and Channel 2 Input Voltage Range VIN Under Voltage Lock Out threshold UVLO Hysteresis Quiescent Current IQ I OUT = 0mA, VFB = VREF + 5% -- 50 70 A Shutdown Current ISHDN EN = GND -- 0.1 1 A Reference Voltage VREF For Adjustable Output Voltage 0.588 0.6 0.612 V Adjustable Output Voltage Range VOUT (Note 6) VREF -- VIN V V VOUT VIN = 2.5V to 5.5V, VOUT = 1.2V 0A < I OUT < 1A 3 -- 3 % 3 -- 3 % 3 -- 3 % 3 -- 3 % 3 -- 3 % VOUT Output Voltage Fix Accuracy VOUT VOUT VOUT VIN = 2.5V to 5.5V, VOUT = 1.3V 0A < I OUT < 1A VIN = 2.5 to 5.5V, VOUT = 1.8V 0A < I OUT < 1A (Note 5) VIN = VOUT + V to 5.5V VOUT = 2.5V, 0A < I OUT < 1A (Note 5) VIN = VOUT + V to 5.5V VOUT = 3.3V, 0A < I OUT < 1A Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8020-07 August 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8020 Parameter Symbol Test Conditions Min Typ Max Unit 3 -- 3 % 50 -- 50 nA VIN = 2.5V -- 0.38 -- VIN = 3.6V -- 0.28 -- VIN = 2.5V -- 0.35 -- VIN = 3.6V -- 0.25 -- VOUT VIN = VOUT + V to 5.5V 0A < IOUT < 1A FB Input Current IFB 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 ILIM_P VIN = 2.5V to 5.5 V 1.4 1.5 -- Logic-High VEN_H VIN = 2.5V to 5.5V 1.5 -- VIN Logic-Low VEN_L VIN = 2.5V to 5.5V -- -- 0.4 Oscillator Frequency fOSC VIN = 3.6V, IOUT = 100mA 1.2 1.5 1.8 MHz Thermal Shutdown Temperature TSD -- 160 -- C 100 -- -- % 1 -- 1 A Output Voltage Accuracy EN Input Voltage Adjustable (Note 5) Maximum Duty Cycle LX Leakage Current ILX VIN = 3.6V, V LX = 0V or VLX = 3.6V   A 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 recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. ΔV = IOUT x PRDS(ON) Note 6. Guarantee by design. Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS8020-07 August 2014 RT8020 Typical Operating Characteristics Efficiency vs. Output Current Efficiency vs. Output Current 100 100 90 80 70 80 Efficiency (%) Efficiency (%) 90 VIN = 3.6V VIN = 4.2V VIN = 5.0V 60 50 40 30 70 VIN VIN VIN VIN 60 50 10 40 30 10 VOUT = 3.3V, L = 4.7μH, COUT = 4.7μF VOUT = 1.2V, L = 4.7μH, COUT = 4.7μF 0 0 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 1 Output Current (A) Output Current (A) Efficiency vs. Output Current UVLO Threshold vs. Temperature 100 2.00 90 1.90 70 VIN VIN VIN VIN 60 50 = = = = UVLO Threshold (V) 80 Efficiency (%) 5.0V 3.6V 3.3V 2.5V 20 20 5.0V 3.6V 3.3V 2.5V 40 30 20 Rising 1.80 1.70 1.60 Falling 1.50 1.40 1.30 10 VOUT = 1.2V, IOUT = 0A VOUT = 1.2V, L = 2.2μH, COUT = 10μF 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.20 1 -40 -25 -10 Output Current (A) 1.15 1.5 1.10 1.4 EN Pin Threshold (V) 1.6 1.05 Rising 0.95 0.90 Falling 0.85 20 35 50 65 80 95 110 125 EN Pin Threshold vs. Temperature 1.20 1.00 5 Temperature (°C) PinThreshold Threshold vs. ENEN Pin vs. Input InputVoltage Voltage EN Pin Threshold (V) = = = = 0.80 0.75 1.3 1.2 1.1 1.0 Rising 0.9 0.8 Falling 0.7 0.6 0.70 0.65 VOUT = 1.2V, IOUT = 0A 0.5 VIN = 3.6V, VOUT = 1.2V, IOUT = 0A 0.4 0.60 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8020-07 August 2014 5.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8020 Output Voltage vs. Temperature 1.25 1.225 1.24 1.220 1.23 1.215 Output Voltage (V) Output Voltage (V) Output Voltage vs. Loading Current 1.230 VIN = 5.0V 1.210 1.205 VIN = 3.6V 1.200 1.195 1.190 1.22 1.21 1.20 1.19 1.18 1.17 1.185 1.16 1.180 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 -40 -25 -10 Loading Current (A) 1.55 1.55 1.50 1.5 Frequency(kHz) 1.6 1.45 1.40 1.35 1.30 VIN = 3.6V, VOUT = 1.2V, IOUT = 300mA 2.8 3.1 3.4 3.7 4 4.3 4.6 65 80 95 110 125 1.35 1.3 4.9 5.2 VIN = 3.6V, VOUT = 1.2V, IOUT = 300mA 1.2 -40 -25 -10 5.5 5 20 35 50 65 80 95 110 125 Temperature (°C) Output Current Limit vs. Input Voltage Output Current Limit vs. Temperature 2.4 2.4 2.3 2.3 2.2 2.2 Output Current Limit (A) Output Current Limit (A) 50 1.4 Input Voltage (V) 2.1 2.0 1.9 1.8 1.7 1.6 1.5 1.4 35 1.45 1.25 1.25 2.5 20 Switching Frequency vs. Temperature 1.60 1.20 5 Temperature (°C) Switching Frequency vs. Input Voltage Frequency(kHz) VIN = 3.6V, IOUT = 0A 1.15 1 VOUT = 1.2V @ TA = 25°C VOUT = 1.2V VIN = 5.0V 2.1 2.0 VIN = 3.6V 1.9 1.8 VIN = 3.3V 1.7 1.6 1.5 1.4 1.3 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 5.5 -40 -25 -10 5 20 35 50 65 80 95 110 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS8020-07 August 2014 RT8020 Power On from EN Power On from EN VIN = 3.6V, VOUT = 1.2V, IOUT = 1A VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA VEN (2V/Div) VEN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) I IN (500mA/Div) I IN (500mA/Div) Time (100μs/Div) Time (100μs/Div) Power On from VIN Power Off from EN VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA VIN = 3.6V, VOUT = 1.2V, IOUT = 10mA VIN (2V/Div) VEN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) ILX (1A/Div) ILX (1A/Div) Time (250μs/Div) Time (100μs/Div) Load Transient Response Load Transient Response VIN = 3.6V, VOUT = 1.2V, IOUT = 50mA to 1A VIN = 3.6V, VOUT = 1.2V, IOUT = 50mA to 0.5A VOUT (50mV/Div) VOUT (50mV/Div) IOUT (500mA/Div) IOUT (500mA/Div) Time (50μs/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8020-07 August 2014 Time (50μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8020 Load Transient Response Load Transient Response VIN = 5.0V, VOUT = 1.2V, IOUT = 50mA to 1A VIN = 5.0V, VOUT = 1.2V, IOUT = 50mA to 0.5A VOUT (50mV/Div) VOUT (50mV/Div) IOUT (500mA/Div) IOUT (500mA/Div) Time (50μs/Div) Time (50μs/Div) Ripple Ripple VIN = 5.0V, VOUT = 1.2V, IOUT = 1A VIN = 3.6V, VOUT = 1.2V, IOUT = 1A VOUT (10mV/Div) VOUT (10mV/Div) VLX (2V/Div) VLX (2V/Div) Time (500ns/Div) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 Time (500ns/Div) is a registered trademark of Richtek Technology Corporation. DS8020-07 August 2014 RT8020 Applications Information The basic RT8020 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  ∆IL   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   L(MAX)   IN(MAX)   Inductor Core Selection Once the value for L is known, the type of inductor must be selected. High efficiency converters generally cannot afford the core loss found in low cost powdered iron cores, forcing the use of 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 copper losses will increase. Ferrite designs have very low core losses and are preferred at high switching frequencies, so design goals can concentrate on copper loss and preventing saturation. Ferrite core material saturates “hard”, which means that inductance collapses abruptly when the peak design current is exceeded. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8020-07 August 2014 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 style inductor to use mainly depend 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 offer much relief. Note that ripple current ratings from capacitor manufacturers are often based on only 2000 hours of life 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 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 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  ∆VOUT  ∆IL ESR   8fC OUT   is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8020 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 values, 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. For adjustable voltage mode, the output voltage is set by an external resistive divider according to the following equation : VOUT = VREF x (1+ R1/R2) Where VREF is the internal reference voltage (0.6V typical) 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 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 oppears 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. Output Voltage Programming The resulting ΔQ/Δt is the current out of VIN that is typically larger than the DC bias current. In continuous mode, The resistive divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 3. IGATECHG = f(QT + QB) VOUT R1 FB RT8020 R2 GND Figure 3. Setting the Output Voltage Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 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, R SW and external inductor RL. In continuous mode the average output current flowing is a registered trademark of Richtek Technology Corporation. DS8020-07 August 2014 RT8020 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) and the duty cycle (DC) is shown as follows : Maximum Power Dissipation (W) 1.8 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. Four-Layer PCB 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 4. De-rating Curves for RT8020 Package Thermal Considerations Checking Transient Response The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junction to ambient. The maximum power dissipation can be calculated by following formula : The regulator loop response can be checked by looking at the load transient response. Switching regulators take 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 that would indicate a stability problem. PD(MAX) = ( TJ(MAX) − TA ) / θJA Where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. For recommended operating conditions specification of RT8020 DC/DC converter, where 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 WDFN-12L 3x3 packages, the thermal resistance θJA is 60°C/W on the standard JEDEC 51-7 four-layers thermal test board. The maximum power dissipation at TA = 25°C can be calculated by following formula : PD(MAX) = (125°C − 25°C) / (60°C/W) = 1.667W for WDFN-12L 3x3 packages The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA. For RT8020 packages, the Figure 4 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS8020-07 August 2014 Layout Considerations Follow the PCB layout guidelines for optimal performance of RT8020.  For the main current paths, keep their traces short and wide.  Put the input capacitor as close as possible to the device pins (VIN and GND).  LX node is with high frequency voltage swing and should be kept 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 RT8020.  Connect all analog grounds to a command node and then connect the command node to the power ground behind the output capacitors. is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8020 Table 1. Recommended Inductors Component Supplier Series Inductance (H) DCR (m) Current Rating (mA) Dimensions (mm) TAIYO YUDEN NR 3015 2.2 60 1480 3 x 3 x 1.5 TAIYO YUDEN NR 3015 4.7 120 1020 3 x 3 x 1.5 Sumida CDRH2D14 2.2 75 1500 4.5 x 3.2 x 1.55 Sumida CDRH2D14 4.7 135 1000 4.5 x 3.2 x 1.55 GOTREND GTSD32 2.2 58 1500 3.85 x 3.85 x 1.8 GOTREND GTSD32 4.7 146 1100 3.85 x 3.85 x 1.8 Table 2. Recommended Capacitors for CIN and COUT Component Supplier Part No. Capacitance (F) Case Size TDK C1608JB0J475M 4.7 0603 TDK C2012JB0J106M 10 0805 MURATA GRM188R60J475KE19 4.7 0603 MURATA GRM219R60J106ME19 10 0805 TAIYO YUDEN JMK107BJ475RA 4.7 0603 TAIYO YUDEN JMK107BJ106MA 10 0603 TAIYO YUDEN JMK212BJ106RD 10 0805 Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS8020-07 August 2014 RT8020 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 Option1 2.300 2.650 0.091 0.104 Option2 1.970 2.070 0.078 0.081 2.950 3.050 0.116 0.120 Option1 1.400 1.750 0.055 0.069 Option2 1.160 1.260 0.046 0.050 D2 E E2 e L 0.450 0.350 0.018 0.450 0.014 0.018 W-Type 12L DFN 3x3 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. DS8020-07 August 2014 www.richtek.com 15