® RT7272B 3A, 36V, 500kHz Synchronous Step-Down Converter General Description Features The RT7272B is a high efficiency, current mode synchronous step-down DC/DC converter that can deliver up to 3A output current over a wide input voltage range from 4.5V to 36V. The device integrates a 150mΩ high side and a 80mΩ low side MOSFET to achieve high conversion efficiency up to 95%. The current mode control architecture supports fast transient response and simple compensation circuit. z 4.5V to 36V Input Voltage Range z 3A Output Current Internal N-MOSFETs Current Mode Control Fixed Frequency Operation : 500kHz Adjustable Output Voltage from 0.8V to 30V High Efficiency Up to 95% Stable with Low ESR Ceramic Output Capacitors Cycle-by-Cycle Current Limit Input Under Voltage Lockout Output Under Voltage Protection Thermal Shutdown Protection Adjustable Current Limit RoHS Compliant and Halogen Free A cycle-by-cycle current limit function provides protection against shorted output and an internal soft-start eliminates input current surge during start-up. The RT7272B provides complete protection functions such as input under voltage lockout, output under voltage protection, over current protection and thermal shutdown. The RT7272B is available in the thermal enhanced SOP-8 (Exposed Pad) package. z z z z z z z z z z z z Applications z z Ordering Information z RT7272B z Package Type SP : SOP-8 (Exposed Pad-Option 2) z z Lead Plating System G : Green (Halogen Free and Pb Free) z Note : z Richtek products are : z ` Distributed Power Systems Pre-Regulator for Linear Regulators Notebook Computers Point of Load Regulator in Distributed Power System Digital Set-top Boxes Personal Digital Recorders Broadband Communications Flat Panel TVs and Monitors Vehicle Electronics RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit VIN BOOT VIN CIN RT7272B CB L SW VOUT R1 RLIM CC R C GND Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS7272B-01 January 2013 COUT FB RL R2 COMP is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT7272B Marking Information Pin Configurations (TOP VIEW) RT7272BGSP : Product Number 8 SW BOOT 2 EN 3 GND 4 GND RT7272B GSPYMDNN VIN 7 RLIM 6 COMP 5 FB 9 YMDNN : Date Code SOP-8 (Exposed Pad) Functional Pin Description Pin No. Pin Name 1 SW 2 BOOT 3 EN 4, 9 (Exposed Pad) Pin Function Switch Node Connect to external L-C filter. Bootstrap Supply for High Side Gate Drive. A 100nF or greater capacitor is recommended to connect from BOOT pin to SW pin. Enable Control Input. A logic-high enables the converter; a logic-low forces the device into shutdown mode. Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum thermal dissipation. Feedback Input. 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 resistive divider. 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. GND 5 FB 6 COMP 7 RLIM Current Limit Setting. Connect to a resistor to determine current limit. 8 VIN Power Input. The input voltage range is from 4.5V to 36V. Must bypass with a suitable large ceramic capacitor. Function Block Diagram VIN VCC Internal Regulator Oscillator Shutdown VA VCC Comparator 1.2V 0.4V Lockout Comparator - 5kΩ EN 1.7V Slope Comp Foldback Control + - Current Sense Amplifier + - + UV Comparator RSENSE VA BOOT UV + S + R Current Comparator Q 150mΩ Q 80mΩ SW GND VCC 0.8V SS RLIM + +EA - FB Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 COMP is a registered trademark of Richtek Technology Corporation. DS7272B-01 January 2013 RT7272B Operation The RT7272B is a constant frequency, current mode synchronous step-down converter. In normal operation, the high side N-MOSFET is turned on when the S-R latch is set by the oscillator and is turned off when the current comparator resets the S-R latch. While the high side N-MOSFET is turned off, the low side N-MOSFET is turned on to conduct the inductor current until next cycle begins. Error Amplifier The error amplifier adjusts its output voltage by comparing the feedback signal (VFB) with the internal 0.8V reference. When the load current increases, it causes a drop in the feedback voltage relative to the reference. The error amplifier's output voltage then rises to allow higher inductor current to match the load current. Oscillator The internal oscillator runs at fixed frequency 500kHz. In short circuit condition, the frequency is reduced to 75kHz for low power consumption. Soft-Start (SS) An internal current source charges an internal capacitor to build a soft-start ramp voltage. The FB voltage will track the internal ramp voltage during soft-start interval. The typical soft-start time is 2ms. Current Setting The current limit of high side MOSFET is adjustable by an external resistor connected to the RLIM pin. The current limit range is from 2A to 6A. When the inductor current reaches the current limit threshold, the COMP voltage will be clamped to limit the inductor current. UV Comparator If the feedback voltage (VFB) is lower than 0.4V, the UV Comparator will go high to turn off the high side MOSFET. The output under voltage protection is designed to operate in Hiccup mode. When the UV condition is removed, the converter will resume switching. Thermal shutdown Internal Regulator The regulator provides low voltage power to supply the internal control circuits and the bootstrap power for high side gate driver. Enable The over temperature protection function will shut down the switching operation when the junction temperature exceeds 150°C. Once the junction temperature cools down by approximately 20°C, the converter will automatically resume switching. The converter is turned on when the EN pin is higher than 2V. When the EN pin is lower than 0.4V, the converter will enter shutdown mode and reduce the supply current to 0.5μA. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS7272B-01 January 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT7272B Absolute Maximum Ratings (Note 1) −0.3V to 40V −0.3V to (VIN + 0.3V) −0.3V to 6V −0.3V to 40V Supply Input Voltage, VIN ----------------------------------------------------------------------------------------Switch Voltage, SW -----------------------------------------------------------------------------------------------z VBOOT − VSW ---------------------------------------------------------------------------------------------------------z Other Pins Voltage -------------------------------------------------------------------------------------------------z Power Dissipation, PD @ TA = 25°C z z z z z z z 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) ---------------------------------------------------------------------------------------- Recommended Operating Conditions z z z 2.041W 49°C/W 15°C/W 260°C 150°C −65°C to 150°C 2kV (Note 4) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------- 4.5V to 36V Junction Temperature Range -------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 12V, CIN = 20μF, TA = 25°C, unless otherwise specified) Parameter Symbol Shutdown Supply Current Test Conditions Min Typ Max Unit VEN = 0V -- 0.5 3 μA -- 0.9 1.2 mA 0.788 0.8 0.812 V Quiescent Current IQ VEN = 3V, VFB = 0.9V Feedback Reference Voltage VREF 4.5V ≤ VIN ≤ 36V High Side Switch On-Resistance RDS(ON)1 -- 150 -- mΩ Low Side Switch On-Resistance RDS(ON)2 -- 80 -- mΩ -- 0 10 μA 2 -- 6.3 A Min. Duty Cycle, RLIM = 57.6kΩ 1.9 2.5 3.1 Min. Duty Cycle, RLIM = 84.5kΩ 2.7 3.5 4.2 Min. Duty Cycle, RLIM = 137kΩ 4.5 5.5 6.5 -- 1.5 -- High Side Switch Leakage Current VEN = 0V, VSW = 0V Upper Switch Current Limit Range UOC Upper Switch Current Limit UOC (Note 5) Lower Switch Current Limit From Drain to Source Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 A A is a registered trademark of Richtek Technology Corporation. DS7272B-01 January 2013 RT7272B Parameter Symbol Test Conditions Min Typ Max Unit 450 500 550 kHz Oscillation Frequency fOSC1 Short Circuit Oscillation Frequency fOSC2 VFB = 0V -- 75 -- kHz Maximum Duty Cycle DMAX VFB = 0.7V -- 90 -- % Minimum On-Time tON -- 100 -- ns Logic-High VIH 2 -- -- Logic-Low Input Under Voltage Lockout Threshold Input Under Voltage Lockout Hysteresis VIL -- -- 0.4 3.9 4.1 4.3 V ΔVUVLO -- 250 -- mV Thermal Shutdown TSD -- 150 -- °C Thermal Shutdown Hysteresis ΔTSD -- 20 -- °C COMP to Current Sense Transconductance GCS -- 4.7 -- A/V Error Amplifier Transconductance GEA -- 1000 -- μA/V EN Input Voltage VUVLO VIN Rising ΔICOMP = ±10μA 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 is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Note 5. RLIM (kΩ) = [UOC x 24.14 x (1 + 0.024 x (UOC − 3.5)) − 1.3], where UOC is desired upper switch peak current limit value. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS7272B-01 January 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT7272B Typical Application Circuit VIN 4.5V to 36V VIN RT7272B 2 BOOT 3 EN SW 1 8 CIN 10µF x 2 Enable RL 179k 4, 9 (Exposed Pad) GND L VOUT R1 7 RLIM RLIM CB 100nF FB 5 COMP 6 COUT CC RC R2 Table 1. Suggested Component Values VOUT (V) R1 (kΩ) R2 (kΩ) RC (kΩ) L (μH) CC (nF) COUT (μF) 12 47 3.35 47 10 2.7 22 x 2 8 27 3 36 8.2 2.7 22 x 2 5 62 11.8 24 6.8 2.7 22 x 2 3.3 75 24 16 4.7 2.7 22 x 2 2.5 25.5 12 12 3.6 2.7 22 x 2 1.2 30 60 6.8 2.2 2.7 22 x 2 Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS7272B-01 January 2013 RT7272B Typical Operating Characteristics Efficiency vs. Output Current 100 90 90 80 80 70 70 Efficiency (%) Efficiency (%) Efficiency vs. Output Current 100 60 VIN = VIN = VIN = VIN = 50 40 30 4.5V 12V 24V 36V VIN = VIN = VIN = VIN = 60 50 4.5V 12V 24V 36V 40 30 20 20 10 10 VOUT = 3.3V VOUT = 3.3V 0 0 0.01 0 0.1 0.5 1 1.5 2 2.5 3 Output Current (A) Output Current (A) Reference Voltage vs. Input Voltage Reference vs. Temperature 0.810 0.810 Reference Voltage (V) Reference Voltage(V) 0.808 0.805 0.803 0.800 0.798 0.795 0.805 0.800 VIN = VIN = VIN = VIN = 0.795 4.5V 12V 24V 36V 0.793 VIN = 4.5V to 36V, VOUT = 3.3V, IOUT = 0.3A VOUT = 3.3V, IOUT = 0.3A 0.790 0.790 2 9.6 17.2 24.8 32.4 -50 40 -25 0 Input Voltage(V) Output Voltage vs. Output Current 3.37 495 Switching Frequency (kHz)1 500 Output Voltage (V) 3.36 3.35 VIN = VIN = VIN = VIN = 3.33 3.32 4.5V 12V 24V 36V 3.31 3.30 50 75 100 125 Switching Frequency vs. Input Voltage 3.38 3.34 25 Temperature (°C) VOUT = 3.3V, IOUT = 0.1A to 3A 3.29 490 485 480 475 470 465 460 455 VOUT = 3.3V, IOUT = 0.3A 450 0 0.5 1 1.5 2 2.5 Output Current (A) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS7272B-01 January 2013 3 4 8 12 16 20 24 28 32 36 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT7272B Current Limit vs. Temperature 8 490 7 Current Limit (A) Switching Frequency (kHz)1 Switching Frequency vs. Temperature 500 480 470 VIN = VIN = VIN = VIN = 460 4.5V 12V 24V 36V 450 6 5 4 3 VOUT = 3.3V, IOUT = 0.3A 440 VIN = 12V 2 -50 -25 0 25 50 75 100 125 -50 0 25 50 75 100 Temperature (°C) Temperature (°C) Load Transient Response Load Transient Response VOUT (200mV/Div) VOUT (200mV/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 0.3A to 3A Time (250μs/Div) Time (250μs/Div) Switching Switching VOUT (5mV/Div) VSW (5V/Div) VSW (5V/Div) IL (1A/Div) IL (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 1.5A Time (1μs/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. 125 VIN = 12V, VOUT = 3.3V, IOUT = 1.5A to 3A VOUT (5mV/Div) www.richtek.com 8 -25 VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. DS7272B-01 January 2013 RT7272B Power On from EN Power Off from EN VEN (5V/Div) VIN (5V/Div) VOUT (2V/Div) VOUT (2V/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (2.5ms/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS7272B-01 January 2013 VIN = 12V, VOUT = 3.3V, IOUT = 3A Time (2.5ms/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT7272B Application Information Output Voltage Setting Chip Enable Operation The resistive divider allows the FB pin to sense the output voltage as shown in Figure 1. The EN pin is the chip enable input. Pulling the EN pin low (<0.4V) will shutdown the device. During shutdown mode, the RT7272B quiescent current drops to lower than 3μA. Driving the EN pin high (>2.5V, < 18V) will turn on the device again. For external timing control, the EN pin can also be externally pulled high by adding a REN resistor and CEN capacitor from the VIN pin (see Figure 3). VOUT R1 FB RT7272B R2 GND EN VIN REN EN Figure 1. Output Voltage Setting RT7272B CEN GND The output voltage is set by an external resistive voltage divider according to the following equation : VOUT = VREF ⎛⎜ 1+ R1 ⎞⎟ ⎝ R2 ⎠ Where VREF is the reference voltage (0.8V typ.). External Bootstrap Diode Connect a 0.1μF low ESR ceramic capacitor between the BOOT and SW pins. 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 RT7272B. Note that the external boot voltage must be lower than 5.5V 5V 100nF SW Figure 2. External Bootstrap Diode Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 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 4. 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. VIN EN REN 100k EN Q1 RT7272B GND Figure 4. Digital Enable Control Circuit Under Voltage Protection Hiccup Mode BOOT RT7272B Figure 3. Enable Timing Control The RT7272B provides Hiccup Mode Under Voltage Protection (UVP). When the VFB voltage drops below 0.4V, the UVP function will be triggered to shut down switching operation. If the UVP condition remains for a period, the RT7272B will retry automatically. When the UVP condition is removed, the converter will resume operation. The UVP is disabled during soft-start period. is a registered trademark of Richtek Technology Corporation. DS7272B-01 January 2013 RT7272B Hiccup Mode 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. VOUT (2V/Div) Table 2. Suggested Inductors for Typical Application Circuit ILX (2A/Div) IOUT = Short Time (50ms/Div) Figure 5. Hiccup Mode Under Voltage Protection 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 Over Temperature Protection The RT7272B features an Over Temperature Protection (OTP) circuitry to prevent from overheating due to excessive power dissipation. The OTP will shut down switching operation when junction temperature exceeds 150°C. Once the junction temperature cools down by approximately 20°C, the converter will resume operation. To maintain continuous operation, the maximum junction temperature should be lower than 125°C. 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 the 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) ⎣ ⎦ ⎣ ⎦ Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS7272B-01 January 2013 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 approximate RMS current equation is given : 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, two 10μF low ESR ceramic capacitors are suggested. For the suggested capacitor, please refer to Table 3 for more details. 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 + 8fC OUT ⎥⎦ ⎣ is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT7272B The output ripple will be the 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. 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. Thermal Considerations 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 : 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. The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA. 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 PD(MAX) = (TJ(MAX) − TA ) / θJA For recommended operating conditions specification of RT7272B, 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. The maximum power dissipation at TA = 25°C can be calculated by following formula : P D(MAX) = (125°C − 25°C) / (75°C/W) = 1.333W (min.copper area PCB layout) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 Power Dissipation (W) 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. Four-Layer PCB 2.0 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 Curve of Maximum Power Dissipation is a registered trademark of Richtek Technology Corporation. DS7272B-01 January 2013 RT7272B Layout Considerations For best performance of the RT7272B, the following layout guidelines must be strictly followed. (a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°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 RL resistor, compensator and feedback components must be connected as close to the device as possible. (b) Copper Area = 10mm2, θJA = 64°C/W (c) Copper Area = 30mm2 , θJA = 54°C/W (d) Copper Area = 50mm2 , θJA = 51°C/W (e) Copper Area = 70mm2 , θJA = 49°C/W Figure 6. Thermal Resistance vs. Copper Area Layout Design Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS7272B-01 January 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT7272B Input capacitor must be placed as close to the IC as possible. VOUT VIN COUT SW should be connected to inductor by wide and short trace. Keep sensitive components away from this trace and CBOOT. RS * L CIN The RL resistor must be connected as close to the device as possible. Keep sensitive components away. C S* RL CBOOT VIN 8 SW REN BOOT 2 EN 3 GND 4 GND VIN 7 RLIM 6 COMP 5 FB 9 CC R1 VOUT RC CP R2 The REN component must be connected. GND The Compensator and feedback components must be connected as close to the device as possible. * : Option Figure 8. PCB Layout Guide Table 3. Suggested Capacitors for CIN and COUT Location Component Supplier Part No. Capacitance (μF) Case Size CIN MURATA GRM32ER71H475K 4.7 1206 CIN TAIYO YUDEN UMK325BJ475MM-T 4.7 1206 CIN TDK C3225X5R1E106K 10 1206 CIN TAIYO YUDEN TMK316BJ106ML 10 1206 C OUT MURATA GRM31CR60J476M 47 1206 C OUT TDK C3225X5R0J476M 47 1210 C OUT MURATA GRM32ER71C226M 22 1210 C OUT TDK C3225X5R1C22M 22 1210 Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS7272B-01 January 2013 RT7272B Outline Dimension H A M EXPOSED THERMAL PAD (Bottom of Package) Y J X B F C I D Dimensions In Millimeters Symbol Dimensions In Inches 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. DS7272B-01 January 2013 www.richtek.com 15