® RT8296A 3A, 23V, 340kHz Synchronous Step-Down Converter General Description Features The RT8296A is a high efficiency, monolithic synchronous step-down DC/DC converter that can deliver up to 3A output current from a 4.5V to 23V input supply. The RT8296A'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. Fault conditions also include output under voltage protection and thermal shutdown. The low current (<3μA) shutdown mode provides output disconnect, enabling easy power management in battery powered systems. The RT8296A is available in a SOP-8 (Exposed Pad) package. z z z z z z z z z z z z z z z Ordering Information RT8296A Package Type SP : SOP-8 (Exposed Pad-Option 1) ±1.5% High Accuracy Feedback Voltage 4.5V to 23V Input Voltage Range 3A Output Current Integrated N-MOSFET Switches Current Mode Control Fixed Frequency Operation : 340kHz Output Adjustable from 0.8V to 20V Up to 95% Efficiency 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 Applications Industrial and Commercial Low Power Systems z Set Top Box Lead Plating System z LCD Monitors and TVs G : Green (Halogen Free and Pb Free) z Green Electronics/Appliances Z : ECO (Ecological Element with z Point of Load Regulation of High Performance DSPs Halogen Free and Pb free) z Wireless AP/Router H : UVP Hiccup L : UVP Latch-Off z Pin Configurations Note : Richtek products are : ` (TOP VIEW) RoHS compliant and compatible with the current require- ` 8 BOOT ments of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. VIN 2 SW GND 3 GND EN 6 COMP 5 FB 9 4 SS 7 SOP-8 (Exposed Pad) Marking Information RT8296AxZSP RT8296AxGSP RT8296AxZSP : Product Number RT8296AxGSP : Product Number RT8296Ax GSPYMDNN x : H or L YMDNN : Date Code Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8296A-04 May 2013 RT8296Ax ZSPYMDNN x : H or L YMDNN : Date Code is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8296A Typical Application Circuit 2 VIN 4.5V to 23V CIN 10µF x 2 REN 100k CSS 0.1µF BOOT VIN 1 RT8296A SW 3 R1 75k 7 EN 8 SS 4, 9 (Exposed Pad) GND CBOOT L 100nF 10µH FB 5 COMP 6 CC 3.3nF RC 13k VOUT 3.3V/3A COUT 22µF x 2 R2 24k CP Open Table 1. Recommended Component Selection VOUT (V) R1 (kΩ) R2 (kΩ) RC (kΩ) CC (nF) L (μH) COUT (μF) 8 27 3 33 3.3 22 22 x 2 5 62 11.8 20 3.3 15 22 x 2 3.3 75 24 13 3.3 10 22 x 2 2.5 25.5 12 9.1 3.3 6.8 22 x 2 1.5 10.5 12 5.6 3.3 3.6 22 x 2 1.2 12 24 4.3 3.3 3.6 22 x 2 1 3 12 3.6 3.3 2 22 x 2 Functional Pin Description Pin No. Pin Name 1 BOOT 2 VIN Pin Function Bootstrap for High Side Gate Driver. Connect 0.1μF or greater ceramic capacitor from BOOT to SW pins. Input Supply Voltage. Must bypass with a suitably large ceramic capacitor. 3 SW Phase Node. Connect to external L-C filter. 4, 9 (Exposed Pad) GND 5 FB 6 COMP 7 EN 8 SS 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. Enable Input Pin. A logic high enables the converter; a logic low forces the RT8296A 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. 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 13.5ms. Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS8296A-04 May 2013 RT8296A Function Block Diagram VIN Internal Regulator Oscillator Slope Comp Shutdown Comparator VA VCC 1.2V Foldback Control + - 5k EN 0.4V Lockout Comparator 2.7V Current Sense Amplifier + VA - + BOOT UV Comparator + 3V VCC S + R Current Comparator Q 85mΩ Q 85mΩ SW GND 6µA 0.8V SS + +EA - FB Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8296A-04 May 2013 COMP is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8296A Absolute Maximum Ratings z z z z z z z z z z z z (Note 1) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------Switch Node Voltage, VSW --------------------------------------------------------------------------------------Switch Node Voltage, VSW, < 10ns ----------------------------------------------------------------------------BOOT Pin Voltage, VBOOT ---------------------------------------------------------------------------------------VBOOT − VSW --------------------------------------------------------------------------------------------------------Other Pins Input Voltage -----------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C −0.3V to 25V −0.3V to (VIN + 0.3V) −5V to 25.3V −0.3V to 31.3V −0.3V to 6V −0.3V to 6V SOP-8 (Exposed Pad) -------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) SOP-8 (Exposed Pad), θJA --------------------------------------------------------------------------------------SOP-8 (Exposed Pad), θJC -------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) --------------------------------------------------------------------------------------- 1.333W Recommended Operating Conditions z z z 75°C/W 15°C/W 260°C 150°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 Test Conditions Min Typ Max Unit Shutdown Supply Current VEN = 0V -- 0.5 3 μA Supply Current VEN = 3 V, VFB = 0.9V -- 0.8 1.2 mA 0.788 0.8 0.812 V -- 940 -- μA/V RDS(ON)1 -- 85 -- mΩ RDS(ON)2 -- 85 -- mΩ VEN = 0V, VSW = 0V -- 0 10 μA Min. Duty Cycle, VBOOT − VSW = 4.8V -- 5.1 -- A GCS -- 5.4 -- A/V f OSC1 300 340 380 kHz Feedback Reference Voltage Error Amplifier Transconductance High Side Switch On Resistance Low Side Switch On Resistance High Side Switch Leakage Current VFB 4.5V ≤ VIN ≤ 23V GEA ΔIC = ±10μA Upper Switch Current Limit COMP to Current Sense Transconductance Oscillation Frequency Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8296A-04 May 2013 RT8296A Parameter Symbol Test Conditions Min Typ Max Unit Short Circuit Oscillation Frequency fOSC2 VFB = 0V -- 100 -- kHz Maximum Duty Cycle DMAX VFB = 0.7V -- 93 -- % Minimum On Time tON -- 100 -- ns 3.8 4.2 4.5 V -- 320 -- mV Input Under Voltage Lockout Threshold Input Under Voltage Lockout Threshold Hysteresis EN Input Voltage VIN Rising Logic-High VIH 2.7 -- 5.5 Logic-Low VIL -- -- 0.4 V Soft-Start Current ISS VSS = 0V -- 6 -- μA Soft-Start Period tSS CSS = 0.1μF -- 13.5 -- ms Thermal Shutdown TSD -- 150 -- °C 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. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8296A-04 May 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8296A Typical Operating Characteristics Efficiency vs. Output Current Reference Voltage vs. Input Voltage 100 0.820 90 0.815 70 Reference Voltage (V) Efficiency (%) 80 VIN = 4.5V VIN = 12V VIN = 23V 60 50 40 30 20 0.810 0.805 0.800 0.795 0.790 0.785 10 VOUT = 3.3V 0 0.01 0.780 0.1 1 10 4 6 8 10 Output Current (A) Reference Voltage vs. Temperature 14 16 18 20 22 24 Output Voltage vs. Output Current 0.820 3.40 0.815 3.38 3.36 0.810 Output Voltage (V) Reference Voltage (V) 12 Input Voltage (V) 0.805 0.800 0.795 0.790 3.34 3.32 3.30 VIN = 4.5V VIN = 12V VIN = 23V 3.28 3.26 3.24 0.785 3.22 0.780 3.20 -50 -25 0 25 50 75 100 VOUT = 3.3V 0.0 125 0.3 0.6 0.9 Temperature (°C) 1.5 1.8 2.1 2.4 2.7 3.0 Switching Frequency vs. Temperature 400 390 380 Switching Frequency (kHz)1 Switching Frequency (kHz)1 Switching Frequency vs. Input Voltage 400 380 370 360 350 340 330 320 310 1.2 Output Current (A) 360 340 320 300 280 260 VIN = 12V, VOUT = 3.3V, IOUT = 0.5A VOUT = 3.3V, IOUT = 0.5A 240 300 4 6 8 10 12 14 16 18 20 22 Input Voltage (V) Copyright © 2013 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. DS8296A-04 May 2013 RT8296A Current Limit vs. Temperature 8.0 6.0 7.5 5.5 Current Limit (A) Output Current Limit (A) Output Current Limit vs. Input Voltage 6.5 5.0 4.5 4.0 7.0 6.5 6.0 5.5 5.0 3.5 4.5 VOUT = 3.3V 3.0 VIN = 12V, VOUT = 3.3V 4.0 4 6 8 10 12 14 16 18 20 22 24 -50 -25 0 25 50 75 100 Input Voltage (V) Temperature (°C) Load Transient Response Load Transient Response VOUT (100mV/Div) VOUT (100mV/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 0.3A to 3A VIN = 12V, VOUT = 3.3V, IOUT = 1.5A to 3A Time (100μs/Div) Time (100μs/Div) Output Voltage Ripple Output Voltage Ripple VOUT (10mV/Div) VOUT (10mV/Div) VSW (10V/Div) VSW (10V/Div) IL (2A/Div) IL (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A VIN = 12V, VOUT = 3.3V, IOUT = 1.5A Time (2.5μs/Div) Time (2.5μs/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8296A-04 May 2013 125 is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8296A 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 = 3A VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (5ms/Div) Time (5ms/Div) Power On from EN Power Off from EN VEN (5V/Div) VEN (5V/Div) VOUT (2V/Div) VOUT (2V/Div) IL (2A/Div) IL (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (5ms/Div) Time (5ms/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS8296A-04 May 2013 RT8296A Application Information The RT8296A 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 3A. Output Voltage Setting The resistive divider allows the FB pin to sense the output voltage as shown in Figure 1. VOUT Soft-Start The RT8296A 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 13.5ms(typ.). Chip Enable Operation R1 FB RT8296A 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 (0.8V typ.). External Bootstrap Diode Connect a 100nF low ESR ceramic capacitor between the BOOT pin and SW pin. This capacitor provides the gate driver voltage for the high side MOSFET. 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 RT8296A. Note that the external boot voltage must be lower than 5.5V 5V BOOT RT8296A 100nF SW The EN pin is the chip enable input. Pulling the EN pin low (<0.4V) will shutdown the device. During shutdown mode, the RT8296A 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 REN* resistor and CEN* 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 REN 100k Chip Enable VIN CIN BOOT 1 CBOOT RT8296A 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. Figure 2. External Bootstrap Diode Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8296A-04 May 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8296A 2 VIN 12V REN1 100k CIN 10µF BOOT VIN 1 CBOOT L RT8296A SW 3 7 EN VOUT 8V R1 REN2 FB 5 8 SS CSS 4, 9 (Exposed Pad) GND COUT COMP 6 CC RC R2 CP Figure 4. The Resistors can be Selected to Set IC Lockout Threshold Under Voltage Protection Hiccup Mode For the RT8296AH, it provides Hiccup Mode Under Voltage Protection (UVP). When the FB voltage drops below half of the feedback reference voltage, VFB, the UVP function will be triggered and the RT8296AH will shut down for a period of time and then recover automatically. The Hiccup Mode UVP can reduce input current in short-circuit conditions. Latch-Off Mode For the RT8296AL, it provides Latch-Off Mode Under Voltage Protection (UVP). When the FB voltage drops below half of the feedback reference voltage, VFB, UVP will be triggered and the RT8296AL will shutdown in LatchOff Mode. In shutdown condition, the RT8296AL can be reset by EN pin or power input VIN. 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 ⎤⎥ f × L VIN ⎦ ⎣ ⎦ ⎣ 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 Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 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. 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 VIN IRMS = IOUT(MAX) OUT −1 VIN 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, two 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. is a registered trademark of Richtek Technology Corporation. DS8296A-04 May 2013 RT8296A The output ripple, ΔVOUT , is determined by : 1 ⎤ ΔVOUT ≤ ΔIL ⎡⎢ESR + 8fCOUT ⎥⎦ ⎣ inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. The output ripple will be highest at the maximum input Checking Transient Response 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. 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. 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. 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 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 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. 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 2 VIN 4.5V to 23V CIN 10µF x 2 REN* Chip Enable BOOT VIN 1 CBOOT L 100nF 10µH RT8296A 7 EN SW 3 RS* CEN* 8 SS CSS 0.1µF RBOOT* 4, 9 (Exposed Pad) GND VOUT 3.3V/3A R1 75k CS * COUT 22µFx2 FB 5 COMP 6 CC 3.3nF RC 13k R2 24k CP NC * : Optional Figure 5. Reference Circuit with Snubber and Enable Timing Control Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8296A-04 May 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8296A For continuous operation, do not exceed the 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 junction 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 of RT8296A, the maximum junction temperature is 125°C. The junction to ambient thermal resistance θJA is layout dependent. For PSOP-8 package, the thermal resistance θJA is 75°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 : The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA. For RT8296A packages, the Figure 7 of derating curves allows 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 1.8 Copper Area 70mm2 50mm2 30mm2 10mm2 Min.Layout 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 Curves for RT8296A Package P D(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W (min.copper area PCB layout) P D(MAX) = (125°C − 25°C) / (49°C/W) = 2.04W (70mm2copper area PCB layout) 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 (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. (a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W (b) Copper Area = 10mm2, θJA = 64°C/W (c) Copper Area = 30mm2 , θJA = 54°C/W Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS8296A-04 May 2013 RT8296A Layout Consideration Follow the PCB layout guidelines for optimal performance of the RT8296A. ` (d) Copper Area = 50mm2 , θJA = 51°C/W Keep the traces of the main current paths as short and wide as possible. ` 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 at small area. Keep analog components away from the LX node to prevent stray capacitive noise pickup. ` Connect feedback network behind the output capacitors. (e) Copper Area = 70mm2 , θJA = 49°C/W Figure 6. Themal Resistance vs. Copper Area Layout Design Keep the loop area small. Place the feedback components near the RT8296A. ` Connect all analog grounds to a command node and then connect the command node to the power ground behind the output capacitors. ` An example of PCB layout guide is shown in Figure 6 for reference. VIN GND Input capacitor must be placed as close to the IC as possible. VOUT SW GND VIN REN CS CIN 8 BOOT L1 CS* VIN 2 SW GND 3 GND CC SS 7 EN 6 COMP 5 FB 9 4 The feedback components must be connected as close to the device as possible. RS* CP RC R1 R2 VOUT COUT GND SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace. Figure 8. PCB Layout Guide Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8296A-04 May 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8296A Outline Dimension 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. www.richtek.com 14 DS8296A-04 May 2013