RT8284 2A, 23V, 340kHz Synchronous Step-Down Converter General Description Features The RT8284 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 RT8284'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 startup. The RT8284 also provides under voltage protection and thermal shutdown protection. The low current (< 3μA) shutdown mode provides output disconnect, enabling easy power management in battery powered systems. The RT8284 is a available in a SOP-8 and SOP-8 (Exposed Pad) package. 子 电 维 佳 富 市 圳 Ordering Information 5 5 1 8 3 2 Lead Plating System G : Green (Halogen Free and Pb Free) 5- Richtek products are : ` RoHS compliant and compatible with the current require- 5 7 0 3 8 / 诚 28 厦 大 Pin Configurations (TOP VIEW) Suitable for use in SnPb or Pb-free soldering processes. 鼎 Marking Information 市 RT8284GS RT8284GS : Product Number RT8284 GSYMDNN RT8284GSP 圳 YMDNN : Date Code BOOT 8 YMDNN : Date Code SS VIN 2 7 EN SW 3 6 COMP GND 4 5 FB 8 SS 深 RT8284GSP : Product Number RT8284 GSPYMDNN 室 5 0 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 际 国 ments of IPC/JEDEC J-STD-020. ` 4 1 2 25 Package Type S : SOP-8 SP: SOP-8(Exposed Pad-Option 1) Note : 0 5 4 Applications 深 RT8284 ±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 SOP-8 BOOT VIN 2 SW GND 3 GND 7 EN 6 COMP 5 FB 9 4 SOP-8 (Exposed Pad) DS8284-01 March 2011 www.richtek.com 1 RT8284 Typical Application Circuit 2 VIN 4.5V to 23V CIN 10µF 1 CBOOT L 10nF 10µH RT8284 SW 3 REN 100k CSS 0.1µF BOOT VIN R1 26.1k 7 EN 8 SS 4, 9 (Exposed Pad) FB 5 COMP GND CC 3.3nF 6 RC 13k CC (nF) 3.3 3.3 3.3 3.3 3.3 3.3 市 圳 1 1 2 2 5 6 3 4 2 5 VIN GND COMP 厦 大 际 Phase Node. Connect this pin to external L-C filter. 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 divider. For an adjustable output, an external resistive divider is connected to this pin. 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. 国 诚 鼎 市 圳 深 FB 28 Pin Function Input Supply Voltage, 4.5V to 23V. Must bypass with a suitably large ceramic capacitor. SW 5 6 1 8 3 室 5 0 Bootstrap for High-Side Gate Driver. Connect a 10nF or greater ceramic capacitor from BOOT to SW pins. BOOT 5 7 0 3 4, 9 (Exposed Pad) 55 Pin Name 4 1 2 3 8 / 25 深 0 5 4 COUT (μF) 22 x 2 22 x 2 22 x 2 22 x 2 22 x 2 22 x 2 佳 Functional Pin Description Pin No. SOP-8 SOP-8 (Exposed Pad) 子 电 L (μH) 22 15 10 6.8 4.7 3.6 维 富 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 VOUT 3.3V/2A 7 7 EN Enable Input pin. A logic high enables the converter; a logic low forces the RT8284 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. 8 8 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 . www.richtek.com 2 DS8284-01 March 2011 RT8284 Function Block Diagram VIN Internal Regulator Oscillator Foldback Control - 5k EN VA - 0.5V + UV Comparator Lockout Comparator + 2.7V 3V Current Sense Amplifier + Slope Comp Shutdown Comparator VA VCC 1.2V + BOOT S 130m Ω Q SW + R Current Comparator 子 130m Ω Q 电 VCC 维 6µA SS 佳 + + Error Amp 0.923V 富 市 FB 圳 深 25 5 5 1 5- 5 7 0 4 1 2 3 8 / COMP 8 3 2 0 5 4 GND 室 5 0 28 厦 大 际 国 诚 鼎 市 圳 深 DS8284-01 March 2011 www.richtek.com 3 RT8284 Absolute Maximum Ratings (Note 1) Supply Voltage, VIN ----------------------------------------------------------------------------------------------Input Voltage, SW ------------------------------------------------------------------------------------------------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 (Εxposed Pad), θJC --------------------------------------------------------------------------------------Junction Temperature --------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Mode) --------------------------------------------------------------------------------------MM (Machine Mode) ---------------------------------------------------------------------------------------------- 子 电 维 佳 富 市 圳 Recommended Operating Conditions 深 1.111W 1.333W 90°C/W 75°C 15°C 150°C 260°C −40°C to 150°C 0 5 4 4 1 2 3 8 / (Note 4) 25 −0.3V to 25V −0.3V to (VIN + 0.3V) −0.3V to 6V −0.3V to 6V 2kV 200V 室 5 0 Supply Voltage, VIN ----------------------------------------------------------------------------------------------- 4.5V to 23V Junction Temperature Range ------------------------------------------------------------------------------------ −40°C to 125°C Ambient Temperature Range ------------------------------------------------------------------------------------ −40°C to 85°C 5 5 1 8 3 2 Electrical Characteristics 5 5 Shutdown Supply Current Supply Current Symbol Min Typ Max Unit -- 0.5 3 μA -- 0.8 1.2 mA 0.909 0.923 0.937 V -- 940 -- μA/V RDS(ON)1 -- 130 -- mΩ RDS(ON)2 -- 130 -- mΩ -- 0 10 μA 3.5 4.5 -- A -- 1.2 -- A GCS -- 5 -- A/V fOSC1 300 340 380 kHz ICC 07 Feedback Voltage 圳 际 VEN = 0V 国 诚 鼎 市 Low Side Switch-On Resistance Test Conditions VEN = 3 V, VFB = 1V VFB Error Amplifier Transconductance GEA High Side Switch-On Resistance 厦 大 (VIN = 12V, TA = 25°C unless otherwise specified) Parameter 28 4.5V ≦ VIN ≦ 23V ΔI C = ±10μA High Side Switch Leakage Current VEN = 0V, VSW = 0V Upper Switch Current Limit Min.Duty Cycle, VBOOT−SW = 4.8V Low Switch Current Limit COMP to Current Sense Transconductance Oscillator Frequency From Drain to Source 深 Short Circuit Oscillation Frequency fOSC2 VFB = 0V -- 110 -- kHz Maximum Duty Cycle DMAX VFB = 0.7V -- 93 -- % Minimum On-Time tON -- 100 -- ns To be continued www.richtek.com 4 DS8284-01 March 2011 RT8284 Parameter EN Threshold Voltage Symbol Test Conditions Min Typ Max Unit Logic High VIH 2.7 -- 5.5 Logic Low VIL -- -- 0.4 3.8 4.2 4.5 V -- 320 -- mV Input Under Voltage Lockout Threshold VIN Rising Input Under Voltage Lockout Hysteresis V Soft-Start Current VSS = 0V -- 6 -- μA Soft-Start Period CSS = 0.1μF -- 15.5 -- ms -- 150 -- °C Thermal Shutdown TSD 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 子 operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended 电 periods may remain possibility to affect device reliability. 维 0 5 4 Note 2. θJA is measured in natural convection at TA = 25°C on a high-effective thermal conductivity four-layer test board,refer to JEDEC 51-7 thermal measurement standard. The measurement case position of θJC is on the exposeed pad for 佳 SOP-8 (Exposed Pad) package. 富 4 1 2 Note 3. Devices are ESD sensitive. Handling precaution is recommended. 3 8 / 市 Note 4. The device is not guaranteed to function outside its operating conditions. 圳 深 25 5 5 1 8 3 2 5- 5 7 0 室 5 0 28 厦 大 际 国 诚 鼎 市 圳 深 DS8284-01 March 2011 www.richtek.com 5 RT8284 Typical Operating Characteristics Efficiency vs. Output Current 90 0.935 Reference Voltage (V) 0.940 80 Efficiency (%) Reference Voltage vs. Input Voltage 100 VIN = 4.5V VIN = 12V VIN = 23V 70 60 50 40 30 20 0.930 0.925 0.920 0.915 0.910 电 VOUT = 3.3V 0 0.900 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 维 2.0 Output Current (A) 富 Reference Voltage vs. Temperature 市 0.940 0.935 圳 0.930 深 0.925 0.910 -2 0.905 -50 -25 0 07 25 50 Temperature (°C) 100 24 3.31 28 3.30 3.29 VIN = 4.5V VIN = 12V VIN = 23V 厦 3.28 3.27 际 VOUT = 3.3V 3.24 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 Output Current (A) Frequency vs. Temperature 370 Frequency (kHz)1 Frequency (kHz)1 22 380 深 340 20 室 5 0 3.32 3.25 诚 圳 350 18 4 4 3.33 125 市 360 16 大 鼎 370 50 14 Input Voltage (V) 8 / 5 Frequency vs. Input Voltage 380 12 1 2 3 3.35 国 75 10 3.26 VIN = 12V, VOUT = 3.3V 55 0.900 8 Output Voltage vs. Output Current 3.34 1 8 3 0.915 VIN = 4.5V to 23V, VOUT = 3.3V, IOUT = 0A 6 3.36 2 5 5 0.920 4 佳 Output Voltage (V) 0.0 Reference Voltage (V) 子 0.905 10 330 320 310 360 350 340 330 320 310 VOUT = 3.3V, IOUT = 0A 300 VIN = 12V, VOUT = 3.3V, IOUT = 0A 300 4 6 8 10 12 14 16 18 Input Voltage (V) www.richtek.com 6 20 22 24 -50 -25 0 25 50 75 100 125 Temperature (°C) DS8284-01 March 2011 RT8284 Current Limit VS. Temperature 6.0 5.5 5.5 Current Limit (A) Current Limit (A) Current Limit vs. Duty cycle 6.0 5.0 4.5 4.0 3.5 5.0 4.5 4.0 子 3.5 电 VIN = 4.5V to 23V, VOUT = 3.3V 3.0 3.0 0 10 20 30 40 50 60 70 80 90 -50 Duty Cycle (%) 富 市 圳 深 IOUT (1A/Div) -2 07 际 圳 深 IL (1A/Div) 100 125 4 4 1 2 3 室 5 0 28 VIN = 12V, VOUT = 3.3V, IOUT = 1A to 2A Switching VOUT (10mV/Div) VSW (10V/Div) IL (1A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (1μs/Div) DS8284-01 March 2011 75 Time (100μs/Div) 诚 市 VOUT (10mV/Div) VSW (10V/Div) 大 鼎 Switching 50 厦 IOUT (1A/Div) 国 Time (100μs/Div) 50 25 Temprature (°C) 8 / 5 2 5 5 VIN = 12V, VOUT = 3.3V, IOUT = 0A to 2A 0 Load Transient Response VOUT (100mV/Div) 1 8 3 55 -25 佳 Load Transient Response VOUT (100mV/Div) 维 100 VIN = 12V, VOUT = 3.3V VIN = 12V, VOUT = 3.3V, IOUT = 1A Time (1μs/Div) www.richtek.com 7 RT8284 Power Off from VIN Power On from VIN VIN (5V/Div) VIN (5V/Div) VOUT (2V/Div) VOUT (2V/Div) IL (2A/Div) IL (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A 维 佳 富 Power On from EN 圳 VOUT (2V/Div) IOUT (2A/Div) Power Off from EN 5 5 1 VOUT (2V/Div) 国 28 厦 大 际 VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (5ms/Div) 室 5 0 VEN (5V/Div) 8 3 2 75 4 1 2 25 5- 0 5 4 Time (5ms/Div) 3 8 / 市 深 VIN = 12V, VOUT = 3.3V, IOUT = 2A 电 Time (5ms/Div) VEN (5V/Div) 子 IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (5ms/Div) 诚 0 鼎 市 圳 深 www.richtek.com 8 DS8284-01 March 2011 RT8284 Application Information Soft-Start The RT8284 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. The RT8284 contains an external soft-start clamp that gradually raises the output voltage. The soft-start timming can be programed 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, it's period will be 15.5ms (typ.). Output Voltage Setting The resistive divider allows the FB pin to sense the output voltage as shown in Figure 1. VOUT Chip Enable Operation R1 RT8284 电 R2 GND 维 佳 Figure 1. Output Voltage Setting 富 The output voltage is set by an external resistive voltage divider according to the following equation : 市 VOUT = VFB ⎛⎜ 1+ R1 ⎞⎟ ⎝ R2 ⎠ Where VFB is the feedback reference voltage 0.923V (typ.). 圳 深 External Bootstrap Diode 5 5 1 8 3 2 driver voltage for the high side MOSFET. 5- 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 RT8284. Note that the external boot voltage must be lower than 5.5V 5V 诚 0 鼎 市 圳 深 BOOT RT8284 10nF SW Figure 2. External Bootstrap Diode DS8284-01 March 2011 3 8 / 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. 厦 大 际 室 5 0 28 VIN 国 0 5 4 4 1 2 25 Connect a 10nF low ESR ceramic capacitor between the BOOT pin and SW pin. This capacitor provides the gate 75 The EN pin is the chip enable input. Pulling the EN pin low (<0.4V) will shutdown the device. During shutdown mode, the RT8284 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). 子 FB REN 100k Chip Enable 2 BOOT VIN CIN 1 CBOOT RT8284 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 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. www.richtek.com 9 RT8284 2 VIN 12V REN1 100k CIN 10µF BOOT VIN 1 CBOOT L RT8284 7 EN SW 3 R1 REN2 COUT COMP GND 6 CC 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 R2 RC CP Figure 4. The Resistors can be Selected to Set IC Lockout Threshold 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 : 子 Hiccup Mode 电 For the RT8284, it provides Hiccup Mode Under Voltage Protection (UVP). When the FB voltage drops below 0.5V, VFB, the UVP function will be triggered and the RT8284 will shut down for a period of time and then recover automatically. The Hiccup Mode UVP can reduce input current in short-circuit conditions. 维 佳 富 市 圳 Inductor Selection 深 55 1 8 3 V V ΔIL = ⎡⎢ OUT ⎤⎥ × ⎡⎢1− OUT ⎤⎥ VIN ⎦ ⎣ f ×L ⎦ ⎣ 2 5 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. 75 鼎 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− ⎥ ⎥ f × Δ I V L(MAX) ⎦ ⎣ IN(MAX) ⎦ ⎣ 市 圳 深 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. 0 5 4 14 VOUT VIN 2 3 8 VIN −1 VOUT This formula has a maximum at VIN = 2VOUT, where I RMS = IOUT / 2. This simple worst-case condition is commonly used for design because even significant deviations do not offer much relief. 室 5 0 28 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. 厦 大 For the input capacitor, one 10μF low ESR ceramic capacitors are recommended. For the recommended capacitor, please refer to table 3 for more detail. 际 国 诚 0 IRMS = IOUT(MAX) / 5 2 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. www.richtek.com 10 Component Supplier FB 5 8 SS CSS 4, 9 (Exposed Pad) Table 2. Suggested Inductors for Typical Application Circuit VOUT 8V 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 DS8284-01 March 2011 RT8284 packages.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) also begins to charge or discharge COUT generating 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. 子 EMI Consideration 电 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 维 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 佳 富 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. 市 圳 深 1 8 3 2 5 5 7 0 Chip Enable 圳 深 CEN* VIN 7 EN 8 SS CSS 4, 0.1µF 9 (Exposed Pad) * : Optional 诚 鼎 CIN 10µF 市 REN* 3 8 / 室 5 0 28 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 of Layout Consideration. 厦 大 际 国 2 VIN 4.5V to 23V 4 1 2 order to enhance EMI performance, there are two methods to suppress the spike voltage. One is to place an R-C snubber between SW and GND and make them as close as possible to the SW pin (see Figure 5). Another method is adding a resistor in series with the bootstrap capacitor, CBOOT. But this method will decrease the driving 25 55 0 5 4 GND BOOT 1 RBOOT* CBOOT L 10nF 10µH RT8284 SW 3 RS* R1 26.1k CS* FB 5 COMP 6 VOUT 3.3V/2A CC 3.3nF RC 13k COUT 22µFx2 R2 10k CP NC Figure 5. Reference Circuit with Snubber and Enable Timing Control DS8284-01 March 2011 www.richtek.com 11 RT8284 Thermal Considerations 6.b) reduces the θJA to 64°C/W. Even further, increasing 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 : 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. For RT8284 packages, the Figure 7 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power dissipation allowed. 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. 2.2 Power Dissipation (W) For recommended operating conditions specification of RT8284, 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 富 市 圳 55 1 8 3 P D(MAX) = (125°C − 25°C) / (75°C/W) = 1.33W (min. copper area PCB layout with SOP-8 Exposed Pad) 2 5 P D(MAX) = (125°C − 25°C) / (49°C/W) = 2.04W (70mm2 copper area PCB layout with SOP-8 Exposed Pad) 5 7 0 1.6 维 1.4 0 5 4 4 1 2 1.2 1.0 0.8 3 8 / 25 Four-Layer PCB 电 1.8 佳 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 : 深 子 2.0 0.6 0.4 室 5 0 0.2 0.0 0 25 50 75 Copper Area 70mm2 50mm2 30mm2 10mm2 Min.Layout SOP-8 100 125 28 Ambient Temperature (°C) Figure 7. Derating Curves for RT8284 Package 厦 大 际 国 P D(MAX) = (125°C − 25°C) / (90°C/W) = 1.11W (min. copper area PCB layout with SOP-8) 诚 鼎 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. 市 (a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W 圳 深 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 (Exposed Pad) pad (Figure 6.a), θJA is 75°C/W. Adding copper area of pad under the SOP-8 (Exposed Pad) (Figure www.richtek.com 12 (b) Copper Area = 10mm2, θJA = 64°C/W DS8284-01 March 2011 RT8284 Layout Consideration For best performance of the RT8284, the follow layout giidelines 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 子 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. 电 维 (d) Copper Area = 50mm2 , θJA = 51°C/W 市 圳 1 8 3 Table 3. Suggested Capacitors for CIN and COUT CIN CIN 75 MURATA 际 4 GND 6 COMP 5 FB 9 GND 厦 Case Size 诚 10 1206 C3225X5R1E106K 10 1206 TMK316BJ106ML 10 1206 MURATA 47 1206 COUT 圳 GRM31CR60J476M TDK C3225X5R0J476M 47 1210 MURATA GRM32ER71C226M 22 1210 TDK C3225X5R1C22M 22 1210 DS8284-01 March 2011 VOUT 28 COUT COUT RC R1 R2 室 5 0 TAIYO YUDEN 深 CP Figure 8. PCB Layout Guide CIN COUT REN VIN Capacitance (μF) Part No. 鼎 市 3 EN 大 GRM31CR61E106K TDK SW GND SS 7 国 Component Supplier 0 2 83 5/ Figure 6. Themal Resistance vs. Copper Area Layout Design 4 1 2 VIN CC 8 L1 SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. 2 5 5 (e) Copper Area = 70mm2 , θJA = 49°C/W 0 5 4 CSS BOOT RS CS COUT VOUT 深 Location CIN 佳 富 2 5 SW GND VIN GND www.richtek.com 13 RT8284 Outline Dimension H A M J B F 子 电 C I 维 佳 D 富 圳 深 A B 市 Min 4.801 1.346 D 0.330 5- 5 7 0 0.150 1.753 0.053 M 0.400 鼎 市 0.007 0.010 0.254 0.002 0.010 6.200 0.228 0.244 1.270 0.016 0.050 大 际 国 诚 0.069 0.053 0.254 5.791 0.157 0.047 0.170 J 厦 0.197 0.020 1.346 0.050 28 Max 0.013 1.194 I 0.189 0.508 23 H 3.988 室 5 0 Min 25 81 C F 5.004 Max Dimensions In Inches 55 3.810 4 1 2 3 8 / Dimensions In Millimeters Symbol 0 5 4 8-Lead SOP Plastic Package 圳 深 www.richtek.com 14 DS8284-01 March 2011 RT8284 H A M EXPOSED THERMAL PAD (Bottom of Package) Y J X B F 子 C I Min 4.801 圳 B 深 C 0.170 0.254 市 圳 Y 0.157 0.000 0.152 5.791 室 5 0 0.053 28 厦 0.069 0.020 0.053 0.010 0.000 0.006 6.200 0.228 0.244 1.270 0.016 0.050 2.300 0.079 0.091 2.000 2.300 0.079 0.091 2.100 2.500 0.083 0.098 3.000 3.500 0.118 0.138 2.000 大 际 国 诚 鼎 0.150 0.007 X X 0.197 0.047 0.406 Option 2 0.189 1.346 -2 Y Max 5 5 1 38 M Min 0.013 1.194 J 4 1 2 Dimensions In Inches 0.510 F I 07 1.753 0 5 4 83 5.004 4.000 1.346 0.330 H Max / 5 2 3.810 D Option 1 富 市 A 55 佳 Dimensions In Millimeters Symbol 电 维 D 8-Lead SOP (Exposed Pad) Plastic Package 深 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. DS8284-01 March 2011 www.richtek.com 15