® RT8284N 2A, 23V, 340kHz Synchronous Step-Down Converter General Description The RT8284N is a high efficiency, monolithic synchronous step down DC/DC converter that can deliver up to 2A output current from a 4.5V to 23V input supply. The RT8284N's current mode architecture and external compensation allow the transient response to be optimized over a wide range of loads and output capacitors. Cycle-by-cycle current limit provides protection against shorted outputs and soft-start eliminates input current surge during start up. The RT8284N also provides under voltage protection and thermal shutdown protection. The low current (< 3μA) shutdown mode provides output disconnection, enabling easy power management in battery-powered systems. The RT8284N is a available in a SOP-8 and SOP-8 (Exposed Pad) package. Features ±1.5% High Accuracy Feedback Voltage Input Voltage Range : 4.5V to 23V 2A Output Current Integrated N-MOSFETs Current Mode Control 340kHz Fixed Frequency Operation Output Adjustable Voltage Range : 0.923V to 20V Efficiency Up to 95% Programmable Soft-Start Stable with Low ESR Ceramic Output Capacitors Cycle-by-Cycle Over Current Protection Input Under Voltage Lockout Output Under Voltage Protection Thermal Shutdown Protection RoHS Compliant and Halogen Free Ordering Information Applications RT8284N Package Type S : SOP-8 SP: SOP-8 (Exposed Pad-Option 1) Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : ` RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Wireless AP/Router Set-Top-Box Industrial and Commercial Low Power Systems LCD Monitors and TVs Green Electronics/Appliances Point of Load Regulation of High-Performance DSPs Pin Configurations (TOP VIEW) Suitable for use in SnPb or Pb-free soldering processes. Marking Information RT8284NGS RT8284NGS : Product Number RT8284N GSYMDNN 8 BOOT 7 EN SW GND 3 6 COMP 4 5 FB 8 SS YMDNN : Date Code SOP-8 BOOT RT8284NGSP RT8284NGSP : Product Number RT8284N GSPYMDNN SS VIN 2 YMDNN : Date Code Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8284N-03 May 2012 VIN 2 SW GND 3 GND 7 EN 6 COMP 5 FB 9 4 SOP-8 (Exposed Pad) is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8284N Typical Application Circuit 2 VIN 4.5V to 23V CIN 10µF REN 100k CSS 0.1µF BOOT VIN 1 RT8284N SW 3 7 EN 8 SS 4, 9 (Exposed Pad) GND CBOOT L 10nF 10µH R1 26.1k FB 5 COMP 6 CC 3.3nF RC 13k VOUT 3.3V/2A COUT 22µF x 2 R2 10k CP Open Recommended Component Selection VOUT (V) R1 (kΩ) R2 (kΩ) RC (kΩ) 8 76.8 10 27 5 45.3 10 20 3.3 26.1 10 13 2.5 16.9 10 9.1 1.8 9.53 10 5.6 1.2 3 10 3.6 CC (nF) 3.3 3.3 3.3 3.3 3.3 3.3 L (μH) 22 15 10 6.8 4.7 3.6 COUT (μF) 22 x 2 22 x 2 22 x 2 22 x 2 22 x 2 22 x 2 Functional Pin Description Pin No. Pin Name Pin Function SOP-8 SOP-8 (Exposed Pad) 1 1 BOOT Bootstrap for High Side Gate Driver. Connect a 10nF or greater ceramic capacitor from BOOT to SW pins. 2 2 VIN Input Supply Voltage, 4.5V to 23V. Must bypass with a suitably large ceramic capacitor. 3 3 SW Phase Node. Connect this pin to external L-C filter. 4 4, GND 9 (Exposed Pad) Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. Feedback Input Pin. This pin is connected to the converter output. It is used to set the output of the converter to regulate to the desired value via an internal resistive voltage divider. For an adjustable output, an external resistive voltage divider is connected to this pin. 5 5 FB 6 6 COMP Compensation Node. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND. In some cases, an additional capacitor from COMP to GND is required. EN Enable Input pin. A logic high enables the converter; a logic low forces the RT8284N into shutdown mode reducing the supply current to less than 3μA. Attach this pin to VIN with a 100kΩ pull up resistor for automatic startup. SS Soft-Start Control Input. SS controls the soft-start period. Connect a capacitor from SS to GND to set the soft-start period. A 0.1μF capacitor sets the soft-start period to 15.5ms . 7 8 7 8 Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8284N-03 May 2012 RT8284N Function Block Diagram VIN Internal Regulator Oscillator Slope Comp Shutdown VA VCC Comparator 1.2V Foldback Control + - 0.5V Lockout Comparator - 5k EN 2.7V 3V Current Sense Amplifier + VA - + BOOT UV Comparator + + Current Comparator VCC S Q R Q 130m Ω SW 130m Ω GND 6µA SS 0.923V + + Error Amp FB Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8284N-03 May 2012 COMP is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8284N Absolute Maximum Ratings (Note 1) Supply Voltage, VIN ----------------------------------------------------------------------------------------------Input Voltage, SW -------------------------------------------------------------------------------------------------<20ns ----------------------------------------------------------------------------------------------------------------VBOOT − VSW --------------------------------------------------------------------------------------------------------Other Pins Voltages ----------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C SOP-8 ----------------------------------------------------------------------------------------------------------------SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOP-8, θJA ----------------------------------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) --------------------------------------------------------------------------------------- Recommended Operating Conditions −0.3V to 25V −0.3V to (VIN + 0.3V) −3V to (VIN + 3V) −0.3V to 6V −0.3V to 6V 1.111W 1.333W 90°C/W 75°C 15°C 150°C 260°C −65°C to 150°C 2kV (Note 4) Supply Voltage, VIN ----------------------------------------------------------------------------------------------- 4.5V to 23V Junction Temperature Range ------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 12V, TA = 25°C unless otherwise specified) Parameter Symbol Shutdown Supply Current Test Conditions Min Typ Max Unit VEN = 0V -- 0.5 3 μA -- 0.8 1.2 mA 0.909 0.923 0.937 V -- 940 -- μA/V Supply Current ICC VEN = 3 V, VFB = 1V Feedback Voltage VFB 4.5V ≤ VIN ≤ 23V Error Amplifier Transconductance GEA ΔIC = ±10μA High Side Switch-On Resistance RDS(ON)1 -- 130 -- mΩ Low Side Switch-On Resistance RDS(ON)2 -- 130 -- mΩ High Side Switch Leakage Current VEN = 0V, VSW = 0V -- 0 10 μA Upper Switch Current Limit Min.Duty Cycle, VBOOT−SW = 4.8V -- 4.3 -- A Low Switch Current Limit COMP to Current Sense Transconductance Oscillator Frequency From Drain to Source -- 1.3 -- A GCS -- 4 -- A/V fOSC1 300 340 380 kHz Short Circuit Oscillation Frequency fOSC2 -- 100 -- kHz VFB = 0V Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8284N-03 May 2012 RT8284N Parameter Symbol Test Conditions Min Typ Max Unit -- 93 -- % ns Maximum Duty Cycle DMAX Minimum On-Time tON -- 100 -- Logic-High VIH 2.7 -- 5.5 Logic-Low VIL -- -- 0.4 3.8 4.2 4.5 V -- 320 -- mV EN Input Threshold Voltage VFB = 0.7V Input Under Voltage Lockout Threshold VUVLO Input Under Voltage Lockout Hysteresis ΔVUVLO Soft-Start Current ISS VSS = 0V -- 6 -- μA Soft-Start Period tSS CSS = 0.1μF -- 15.5 -- ms -- 150 -- °C Thermal Shutdown (Note 5) VIN Rising V TSD 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. Guaranteed by design. Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8284N-03 May 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8284N Typical Operating Characteristics Efficiency vs. Output Current Reference Voltage vs. Input Voltage 100 0.940 90 VIN = 4.5V VIN = 12V VIN = 23V 70 0.935 Reference Voltage (V) Efficiency (%) 80 60 50 40 30 0.930 0.925 0.920 0.915 0.910 20 0.905 10 VOUT = 3.3V 0 0.900 0 0.25 0.5 0.75 1 1.25 1.5 1.75 2 4 6 8 10 Output Current (A) Reference Voltage vs. Temperature 16 18 20 22 24 3.36 3.35 0.935 3.34 0.930 Output Voltage (V) Reference Voltage (V) 14 Output Voltage vs. Output Current 0.940 0.925 0.920 0.915 0.910 3.33 3.32 3.31 3.30 VIN = 4.5V VIN = 12V VIN = 23V 3.29 3.28 3.27 3.26 0.905 3.25 VOUT = 3.3V 3.24 0.900 -50 -25 0 25 50 75 100 0 125 0.2 0.4 0.6 Temperature (°C) 0.8 1 1.2 1.4 1.6 1.8 2 Output Current (A) Frequency vs. Temperature Frequency vs. Input Voltage 380 380 370 370 360 360 Frequency (kHz)1 Frequency (kHz)1 12 Input Voltage (V) 350 340 330 320 350 340 330 320 310 310 VOUT = 3.3V, VIN = 12V, IOUT = 0A VOUT = 3.3V, IOUT = 0A 300 300 4 6 8 10 12 14 16 18 20 22 Input Voltage (V) Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 24 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS8284N-03 May 2012 RT8284N Current Limit vs. Temperature Load Transient Response 6.0 Current Limit (A) 5.5 VOUT (100mV/Div) 5.0 4.5 4.0 IOUT (1A/Div) 3.5 VIN = 12V, VOUT = 3.3V VIN = 12V, VOUT = 3.3V, IOUT = 0A to 2A 3.0 -50 -25 0 25 50 75 100 Time (100μs/Div) 125 Temprature (°C) Load Transient Response Switching VOUT (10mV/Div) VOUT (100mV/Div) IL (1A/Div) VSW (10V/Div) IOUT (1A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 1A to 2A VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (100μs/Div) Time (1μs/Div) Power On from VIN Power Off from VIN VIN (5V/Div) VOUT (2V/Div) VIN (5V/Div) VOUT (2V/Div) IL (1A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (10ms/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8284N-03 May 2012 IL (1A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8284N Power On from EN Power Off from EN VEN (2V/Div) VEN (2V/Div) VOUT (2V/Div) VOUT (2V/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (10ms/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (10ms/Div) is a registered trademark of Richtek Technology Corporation. DS8284N-03 May 2012 RT8284N Application Information The RT8284N is a synchronous high voltage buck converter that can support the input voltage range from 4.5V to 23V and the output current can be up to 2A. Output Voltage Setting The resistive voltage divider allows the FB pin to sense the output voltage as shown in Figure 1. Soft-Start The RT8284N contains an external soft-start clamp that gradually raises the output voltage. The soft-start timing can be programmed by the external capacitor between SS pin and GND. The chip provides a 6μA charge current for the external capacitor. If 0.1μF capacitor is used to set the soft-start, the period will be 15.5ms (typ.). VOUT Chip Enable Operation R1 FB RT8284N R2 GND Figure 1. Output Voltage Setting The output voltage is set by an external resistive voltage divider according to the following equation : VOUT = VFB ⎛⎜ 1+ R1 ⎞⎟ ⎝ R2 ⎠ where VFB is the feedback reference voltage 0.923V (typ.). External Bootstrap Diode Connect a 10nF low ESR ceramic capacitor between the BOOT pin and SW pin. This capacitor provides the gate driver voltage for the high side MOSFET. The EN pin is the chip enable input. Pulling the EN pin low (<0.4V) will shut down the device. During shutdown mode, the RT8284N quiescent current drops to lower than 3μA. Driving the EN pin high ( > 2.7V, < 5.5V) will turn on the device again. For external timing control (e.g.RC), the EN pin can also be externally pulled high by adding a R EN* resistor and C EN* capacitor from the VIN pin (see Figure 5). An external MOSFET can be added to implement digital control on the EN pin when no system voltage above 2.5V is available, as shown in Figure 3. In this case, a 100kΩ pull-up resistor, REN, is connected between VIN and the EN pin. MOSFET Q1 will be under logic control to pull down the EN pin. 2 VIN It is recommended to add an external bootstrap diode between an external 5V and BOOT pin for efficiency improvement when input voltage is lower than 5.5V or duty ratio is higher than 65% .The bootstrap diode can be a low cost one such as IN4148 or BAT54. The external 5V can be a 5V fixed input from system or a 5V output of the RT8284N. Note that the external boot voltage must be lower than 5.5V REN 100k Chip Enable VIN CIN BOOT 1 CBOOT RT8284N 7 EN VOUT L SW 3 R1 Q1 8 SS CSS 4, 9 (Exposed Pad) GND COUT FB 5 COMP 6 CC RC R2 CP Figure 3. Enable Control Circuit for Logic Control with Low Voltage 5V BOOT RT8284N 10nF SW Figure 2. External Bootstrap Diode Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8284N-03 May 2012 To prevent enabling circuit when VIN is smaller than the VOUT target value, a resistive voltage divider can be placed between the input voltage and ground and connected to the EN pin to adjust IC lockout threshold, as shown in Figure 4. For example, if an 8V output voltage is regulated from a 12V input voltage, the resistor, REN2, can be selected to set input lockout threshold larger than 8V. is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8284N 2 VIN 12V REN1 100k CIN 10µF VIN BOOT 1 CBOOT L RT8284N 7 EN SW 3 VOUT 8V R1 REN2 8 SS CSS 4, 9 (Exposed Pad) GND COUT FB 5 COMP 6 CC RC R2 CP Figure 4. The Resistors can be Selected to Set IC Lockout Threshold Hiccup Mode For the RT8284N, Hiccup Mode Under Voltage Protection (UVP) is provided. When the FB voltage, VFB, drops below 0.5V, the UVP function will be triggered and the RT8284N will shut down for a period of time and then recover automatically. The Hiccup Mode UVP can reduce input current in short-circuit conditions. Inductor Selection The inductor value and operating frequency determine the ripple current according to a specific input and output voltage. The ripple current ΔIL increases with higher VIN and decreases with higher inductance. V V ΔIL = ⎡⎢ OUT ⎤⎥ × ⎡⎢1− OUT ⎤⎥ VIN ⎦ ⎣ f ×L ⎦ ⎣ Having a lower ripple current reduces not only the ESR losses in the output capacitors but also the output voltage ripple. High frequency with small ripple current can achieve highest efficiency operation. However, it requires a large inductor to achieve this goal. For the ripple current selection, the value of ΔIL = 0.24(IMAX) will be a reasonable starting point. The largest ripple current occurs at the highest VIN. To guarantee that the ripple current stays below the specified maximum, the inductor value should be chosen according to the following equation : ⎡ VOUT ⎤ ⎡ VOUT ⎤ L =⎢ ⎥ × ⎢1 − VIN(MAX) ⎥ f I × Δ L(MAX) ⎣ ⎦ ⎣ ⎦ The inductor's current rating (caused a 40°C temperature rising from 25°C ambient) should be greater than the maximum load current and its saturation current should be greater than the short circuit peak current limit. Please see Table 2 for the inductor selection reference. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 Table 2. Suggested Inductors for Typical Application Circuit Component Supplier Series Dimensions (mm) TDK VLF10045 10 x 9.7 x 4.5 TDK TAIYO YUDEN SLF12565 12.5 x 12.5 x 6.5 NR8040 8x8x4 CIN and COUT Selection The input capacitance, C IN, is needed to filter the trapezoidal current at the source of the high side MOSFET. To prevent large ripple current, a low ESR input capacitor sized for the maximum RMS current should be used. The RMS current is given by : V IRMS = IOUT(MAX) OUT VIN VIN −1 VOUT This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT / 2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. 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. For the input capacitor, one 10μF low ESR ceramic capacitors are recommended. For the recommended capacitor, please refer to table 3 for more detail. The selection of COUT is determined by the required ESR to minimize voltage ripple. Moreover, the amount of bulk capacitance is also a key for COUT selection 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 + 8fCOUT ⎥⎦ ⎣ The output ripple will be highest at the 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 requirement. Dry tantalum, special polymer, aluminum electrolytic and ceramic capacitors are all available in surface mount packages. is a registered trademark of Richtek Technology Corporation. DS8284N-03 May 2012 RT8284N Special polymer capacitors offer very low ESR value. However, it provides lower capacitance density than other types. Although Tantalum capacitors have the highest capacitance density, it is important to only use types that pass the surge test for use in switching power supplies. Aluminum electrolytic capacitors have significantly higher ESR. However, it can be used in cost-sensitive applications for ripple current rating and long term reliability considerations. 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. Checking Transient Response 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) and COUT also begins to be charge or discharged to generate a feedback error signal for 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. EMI Consideration Since parasitic inductance and capacitance effects in PCB circuitry would cause a spike voltage on SW pin when high-side MOSFET is turned-on/off, this spike voltage on SW may impact on EMI performance in the system. In order to enhance EMI performance, there are two methods to suppress the spike voltage. One way is by placing an R-C snubber between SW and GND and locating them as close as possible to the SW pin (see Figure 5). Another method is by adding a resistor in series with the bootstrap capacitor, CBOOT, but this method will decrease the driving 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 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. 2 VIN 4.5V to 23V REN* Chip Enable CIN 10µF capability to the high side MOSFET. It is strongly recommended to reserve the R-C snubber during PCB layout for EMI improvement. Moreover, reducing the SW trace area and keeping the main power in a small loop will be helpful on EMI performance. For detailed PCB layout guide, please refer to the section Layout Considerations. BOOT VIN 1 RBOOT* CBOOT L 10nF 10µH RT8284N 7 EN SW 3 RS* CEN* 8 SS CSS 4, 0.1µF 9 (Exposed Pad) GND VOUT 3.3V/2A R1 26.1k CS* COUT 22µFx2 FB 5 COMP 6 CC 3.3nF RC 13k R2 10k CP NC * : Optional Figure 5. Reference Circuit with Snubber and Enable Timing Control Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8284N-03 May 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8284N For continuous operation, do not exceed absolute maximum operation junction temperature 125°C. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surroundings airflow and temperature difference between junctions to ambient. The maximum power dissipation can be calculated by following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where T J(MAX) is the maximum operation junction temperature, TA is the ambient temperature and the θJA is the junction to ambient thermal resistance. For recommended operating conditions specification, the maximum junction temperature is 125°C. The junction to ambient thermal resistance θJA is layout dependent. For SOP-8 (Exposed Pad) package, the thermal resistance θJA is 75°C/W on the standard JEDEC 51-7 four layers thermal test board. For SOP-8 package, the thermal resistance θJA is 90°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 : P D(MAX) = (125°C − 25°C) / (75°C/W) = 1.33W (min. copper area PCB layout with SOP-8 Exposed Pad) (Exposed Pad) pad (Figure 6.a), θJA is 75°C/W. Adding copper area of pad under the SOP-8 (Exposed Pad) (Figure 6.b) reduces the θJA to 64°C/W. Even further, increasing the copper area of pad to 70mm2 (Figure 6.e) reduces the θJA to 49°C/W. The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA. The of de-rating curves in Figure 7 allow the designer to see the effect of rising ambient temperature on the maximum power dissipation allowed. 2.2 Four-Layer PCB 2.0 Power Dissipation (W) Thermal Considerations Copper Area 70mm2 50mm2 30mm2 10mm2 Min.Layout SOP-8 1.8 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 7. Derating Curve of Maximum Power Dissipation P D(MAX) = (125°C − 25°C) / (49°C/W) = 2.04W (70mm2 copper area PCB layout with SOP-8 Exposed Pad) P D(MAX) = (125°C − 25°C) / (90°C/W) = 1.11W (min. copper area PCB layout with SOP-8) The thermal resistance θJA of SOP-8 (Exposed Pad) is determined by the package architecture design and the PCB layout design. However, the package architecture design had been designed. If possible, it's useful to increase thermal performance by the PCB layout copper design. The thermal resistance θJA can be decreased by adding copper area under the exposed pad of SOP-8 (Exposed Pad) package. As shown in Figure 6, the amount of copper area to which the SOP-8 (Exposed Pad) is mounted affects thermal performance. When mounted to the standard SOP-8 Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 (a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W (b) Copper Area = 10mm2, θJA = 64°C/W is a registered trademark of Richtek Technology Corporation. DS8284N-03 May 2012 RT8284N Layout Considerations For best performance of the RT8284N, the following layout guidelines must be strictly followed. (c) Copper Area = 30mm2 , θJA = 54°C/W ` Input capacitor must be placed as close to the IC as possible. ` SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. ` The feedback components must be connected as close to the device as possible The feedback components must be connected as close to the device as possible. Input capacitor must be placed as close to the IC as possible. SW GND VIN GND CSS (d) Copper Area = 50mm2 , θJA = 51°C/W CIN BOOT RS CS VIN 2 SW 3 GND 4 GND SS 7 EN 6 COMP 5 FB 9 COUT VOUT CC 8 L1 SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. REN VIN CP RC R1 R2 VOUT GND Figure 8. PCB Layout Guide (e) Copper Area = 70mm2 , θJA = 49°C/W Figure 6. Themal Resistance vs. Copper Area Layout Design Table 3. Suggested Capacitors for CIN and COUT Location Component Supplier Part No. Capacitance (μF) Case Size CIN MURATA GRM31CR61E106K 10 1206 CIN TDK C3225X5R1E106K 10 1206 CIN TAIYO YUDEN TMK316BJ106ML 10 1206 COUT MURATA GRM31CR60J476M 47 1206 COUT TDK C3225X5R0J476M 47 1210 COUT MURATA GRM32ER71C226M 22 1210 COUT TDK C3225X5R1C22M 22 1210 Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS8284N-03 May 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8284N Outline Dimension H A M J B F C I D Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 4.801 5.004 0.189 0.197 B 3.810 3.988 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.508 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.170 0.254 0.007 0.010 I 0.050 0.254 0.002 0.010 J 5.791 6.200 0.228 0.244 M 0.400 1.270 0.016 0.050 8-Lead SOP Plastic Package Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS8284N-03 May 2012 RT8284N H A M EXPOSED THERMAL PAD (Bottom of Package) Y J X B F C I D Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 4.801 5.004 0.189 0.197 B 3.810 4.000 0.150 0.157 C 1.346 1.753 0.053 0.069 D 0.330 0.510 0.013 0.020 F 1.194 1.346 0.047 0.053 H 0.170 0.254 0.007 0.010 I 0.000 0.152 0.000 0.006 J 5.791 6.200 0.228 0.244 M 0.406 1.270 0.016 0.050 X 2.000 2.300 0.079 0.091 Y 2.000 2.300 0.079 0.091 X 2.100 2.500 0.083 0.098 Y 3.000 3.500 0.118 0.138 Option 1 Option 2 8-Lead SOP (Exposed Pad) Plastic Package Richtek Technology Corporation 5F, No. 20, Taiyuen 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. DS8284N-03 May 2012 www.richtek.com 15