® RT7247B 2A, 18V, 1.2MHz Synchronous Step-Down Converter General Description Features ±1.5% High Accuracy Reference Voltage The RT7247B is a high efficiency, monolithic synchronous step-down DC/DC converter that can deliver up to 2A output current from a 4.5V to 18V input supply. The RT7247B's current mode architecture and external compensation allow the transient response to be optimized over a wide input range and loads. Cycle-bycycle current limit provides protection against shorted outputs, and soft-start eliminates input current surge during start-up. The RT7247B 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 RT7247B is available in an SOP-8 (Exposed Pad) package. 4.5V to 18V Input Voltage Range 2A Output Current Integrated N-MOSFET Switches Current Mode Control Fixed Frequency Operation : 1.2MHz Output Adjustable from 0.8V to 12V Stable with Low ESR Ceramic Output Capacitors Up to 95% Efficiency Programmable Soft-Start Cycle-by-Cycle Over Current Limit Input Under Voltage Lockout Output Under Voltage Protection Thermal Shutdown Protection RoHS Compliant and Halogen Free Marking Information Applications RT7247BxGSP : Product Number RT7247Bx GSPYMDNN 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 x : H or L YMDNN : Date Code Simplified Application Circuit BOOT VIN VIN CIN CBOOT L RT7247B SW Chip Enable VOUT R1 EN SS CSS CC GND Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7247B-01 September 2012 COUT FB COMP RC R2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT7247B Ordering Information Pin Configurations RT7247B (TOP VIEW) Package Type SP : SOP-8 (Exposed Pad-Option 2) Lead Plating System G : Green (Halogen Free and Pb Free) H : UVP Hiccup L : UVP Latch-Off 8 BOOT VIN 2 SW GND 3 GND EN 6 COMP 5 FB 9 4 SS 7 SOP-8 (Exposed Pad) Note : Richtek products are : ` RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` Suitable for use in SnPb or Pb-free soldering processes. Functional Pin Description Pin No. Pin Name Pin Function 1 BOOT Bootstrap for High Side Gate Driver. Connect a 0.1μF or greater ceramic capacitor from BOOT to SW pins. 2 VIN Input Supply Voltage, 4.5V to 18V. Must bypass with a suitable large ceramic capacitor. 3 SW Switch Node. Connect this pin to an external L-C filter. GND Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 5 FB Feedback Input. It is used to regulate the output of the converter to a set value via an external resistive voltage divider. 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. 7 EN Enable Input. A logic high enables the converter; a logic low forces the IC 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 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 13.5ms. 4, 9 (Exposed Pad) Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS7247B-01 September 2012 RT7247B Function Block Diagram VIN Internal Regulator Oscillator Slope Comp Shutdown V V A CC Comparator 1.2V Foldback Control + - 5kΩ EN 0.4V Lockout Comparator 1.8V Current Sense Amplifier + - RSENSE VA + BOOT UV Comparator + + Current Comparator S Q R Q 150mΩ SW 130mΩ GND VCC 6µA 0.8V SS + +EA - FB COMP Operation Internal Regulator Foldback Control Provide internal power for logic control and switch gate drivers. Dynamically adjust the internal clock. It provides a slower frequency as a lower FB voltage. Shutdown Comparator UV Comparator Activate internal regulator once EN input level is higher than the target level. Force IC to enter shutdown mode when the EN input level is lower than 0.4V. As FB voltage is lower than the UV voltage, it will activate a UV protect scheme. Lockout Comparator The output voltage COMP of the error amplifier is adjusted by comparing FB signal with the internal reference voltage and SS signal. Activate the current comparator, release lock-out logic, and enable the switches as EN input level is higher than lockout threshold voltage. Otherwise, the switches still lock out. Oscillator The oscillator provides internal clock and controls the converter's switching frequency. Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7247B-01 September 2012 Error Amplifier Current Sense Amplifier RSENSE detects the peak current of the high side switch. This signal is amplified by the current sense amplifier and added with a slope compensation signal. Then, It controls the switches by comparing this signal with the COMP voltage. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT7247B Absolute Maximum Ratings (Note 1) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------Switch Voltage, SW -----------------------------------------------------------------------------------------------VBOOT − VSW ---------------------------------------------------------------------------------------------------------Other Pins Voltage -------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C −0.3V to 20V −0.3V to (VIN + 0.3V) −0.3V to 6V −0.3V to 20V 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 75°C/W 15°C/W 260°C 150°C −65°C to 150°C 2kV (Note 4) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------- 4.5V to 18V 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 = 3V, VFB = 0.9V -- 0.8 1.2 mA 0.788 0.8 0.812 V -- 940 -- μA/V RDS(ON)1 -- 150 -- mΩ RDS(ON)2 -- 130 -- mΩ VEN = 0V, VSW = 0V -- 0 10 μA Min. Duty Cycle, VBOOT − VSW = 4.8V -- 4 -- A Reference Voltage Error Amplifier Transconductance High Side Switch On-Resistance Low Side Switch On-Resistance High Side Switch Leakage Current Upper Switch Current Limit VREF 4.5V ≤ VIN ≤ 18V GEA ΔIC = ±10μA COMP to Current Sense Transconductance GCS -- 3.7 -- A/V Oscillation Frequency fOSC1 1 1.2 1.4 MHz Short Circuit Oscillation Frequency fOSC2 VFB = 0V -- 270 -- kHz Maximum Duty Cycle DMAX VFB = 0.7V -- 78 -- % Minimum On-Time tON -- 100 -- ns Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS7247B-01 September 2012 RT7247B Parameter EN Input Threshold Voltage Symbol Test Conditions Min Typ Max Unit Logic-High VIH 2 -- 18 Logic-Low VIL -- -- 0.4 3.8 4.2 4.5 V -- 320 -- mV Input Under Voltage Lockout Threshold Input Under Voltage Lockout Hysteresis VUVLO VIN Rising ΔVUVLO 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 © 2012 Richtek Technology Corporation. All rights reserved. DS7247B-01 September 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT7247B Typical Application Circuit 2 VIN 4.5V to 18V CIN 10µF x 2 Chip Enable CSS 0.1µF BOOT VIN 1 RT7247B SW 3 R1 75k 7 EN 8 SS 4, 9 (Exposed Pad) GND CBOOT L 0.1µF 3.6µH FB 5 COMP 6 CC RC 0.82nF 32k VOUT 3.3V COUT 22µF x 2 R2 24k CP Open Table 1. Suggested Components Selection V OUT (V) R1 (kΩ) R2 (kΩ) RC (kΩ) CC (nF) L (μH) COUT (μF) 8 27 3 75 0.82 10 22 x 2 5 62 11.8 47 0.82 6.8 22 x 2 3.3 75 24 32 0.82 3.6 22 x 2 2.5 25.5 12 25.5 0.82 3.6 22 x 2 1.5 10.5 12 15 0.82 2 22 x 2 1.2 12 24 12 0.82 2 22 x 2 1 3 12 10 0.82 2 22 x 2 Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS7247B-01 September 2012 RT7247B Typical Operating Characteristics Efficiency vs. Output Current Output Voltage vs. Input Voltage 100 3.40 90 3.35 VIN = 5V VIN = 12V VIN = 17V 70 Output Voltage (V) Efficiency (%) 80 60 50 40 30 20 3.30 3.25 3.20 3.15 10 VOUT = 3.3V, IOUT = 0A VOUT = 3.3V 0 3.10 0.01 0.1 1 10 4 6.6 9.2 Output Current (A) 14.4 Output Voltage vs. Output Current 3.40 3.35 3.35 Output Voltage (V) 3.40 3.30 3.25 3.20 3.30 3.25 VIN = 12V VIN = 17V 3.20 3.15 3.15 VOUT = 3.3V VIN = 12V, VOUT = 3.3V 3.10 3.10 -50 -25 0 25 50 75 100 125 0.0 0.4 0.8 Temperature (°C) 1.2 1.6 2.0 Output Current (A) Switching Frequency vs. Input Voltage Switching Frequency vs. Temperature 1.40 1.40 1.35 1.35 Switching Frequency (MHz)1 Switching Frequency (MHz)1 17 Input Voltage (V) Output Voltage vs. Temperature Output Voltage (V) 11.8 1.30 1.25 1.20 1.15 1.10 1.05 1.30 1.25 1.20 VIN = 12V, VOUT = 3.3V VIN = 8V, VOUT = 1.2V 1.15 1.10 1.05 VOUT = 3.3V, IOUT = 0.3A 1.00 IOUT = 0.3A 1.00 4 6.6 9.2 11.8 14.4 Input voltage (V) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7247B-01 September 2012 17 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT7247B Output Current vs. Input Voltage 5.0 4.5 4.5 Output Current (A) Output Current (A) Output Current vs. Temperature 5.0 4.0 3.5 3.0 2.5 4.0 3.5 3.0 2.5 VIN = 8V, VOUT = 1.2V 2.0 VOUT = 3.3V 2.0 -50 -25 0 25 50 75 100 125 4 6.6 9.2 11.8 14.4 Temperature (°C) Input Voltage (V) Load Transient Response Output Ripple Voltage 17 VOUT (5mV/Div) VOUT (100mV/Div) VSW (5V/Div) IOUT (1A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 1A to 2A VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (100μs/Div) Time (500ns/Div) Power On from VIN Power Off from VIN VIN (5V/Div) VIN (5V/Div) VOUT (2V/Div) VOUT (2V/Div) IL (2A/Div) IOUT (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (5ms/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (5ms/Div) is a registered trademark of Richtek Technology Corporation. DS7247B-01 September 2012 RT7247B Power On from EN Power Off from EN VEN (10V/Div) VEN (10V/Div) VOUT (2V/Div) VOUT (2V/Div) IL (2A/Div) IL (2A/Div) VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (5ms/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7247B-01 September 2012 VIN = 12V, VOUT = 3.3V, IOUT = 2A Time (50μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT7247B Application Information Output Voltage Setting Soft-Start The resistive divider allows the FB pin to sense the output voltage as shown in Figure 1. The RT7247B provides soft-start function. The soft-start function is used to prevent large inrush current while converter is being powered-up. The soft-start timing can be programmed by the external capacitor between SS and GND. An internal current source ISS (6μA) charges an VOUT R1 FB RT7247B R2 GND Figure 1. Output Voltage Setting The output voltage is set by an external resistive voltage divider according to the following equation : VOUT = VREF ⎛⎜ 1+ R1 ⎞⎟ ⎝ R2 ⎠ external capacitor to build a soft-start ramp voltage. The VFB voltage will track the internal ramp voltage during softstart interval. The typical soft-start time is calculated as follows : 0.8 × CSS Soft-Start time tSS = , if CSS capacitor ISS is 0.1μF, then soft-start time = 0.8 × 0.1μ ≒ 13.5ms 6μ Chip Enable Operation Where VREF is the reference voltage (0.8V typ.). External Bootstrap Diode Connect a 0.1μF 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 RT7247B. Note that the external boot voltage must be lower than 5.5V 5V BOOT RT7247B The EN pin is the chip enable input. Pulling the EN pin low (<0.4V) will shut down the device. During shutdown mode, the RT7247B quiescent current drops to lower than 3μA. Driving the EN pin high (>2V, <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). EN VIN REN EN RT7247B CEN GND Figure 3. Enable Timing Control An external MOSFET can be added to implement digital control on the EN pin when no system voltage above 2V 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. 0.1µF SW VIN Figure 2. External Bootstrap Diode EN REN 100k EN Q1 RT7247B GND Figure 4. Digital Enable Control Circuit Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS7247B-01 September 2012 RT7247B Under Voltage Protection Hiccup Mode For the RT7247BH, it 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 RT7247BH will retry automatically. When the UVP condition is removed, the converter will resume operation. The UVP is disabled during soft-start period. Over Temperature Protection The RT7247B 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. Hiccup Mode Inductor Selection Time (50ms/Div) 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 the highest efficiency operation. However, it requires a large inductor to achieve this goal. VOUT (500mV/Div) IL (2A/Div) Figure 5. Hiccup Mode Under Voltage Protection Latch-Off Mode For the RT7247BL, 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 RT7247BL will shut down in LatchOff Mode. In shutdown condition, the RT7247BL can be reset by EN pin or power input VIN. Latch-Off Mode VOUT (2V/Div) 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 I V × Δ L(MAX) ⎦ ⎣ IN(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 IL (2A/Div) Time (50ms/Div) 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 NRS8040 8 x8x4 Figure 6. Latch-Off Mode Under Voltage Protection Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7247B-01 September 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT7247B CIN and COUT Selection Thermal Considerations 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 is given : 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 : V IRMS = IOUT(MAX) OUT VIN VIN −1 VOUT This formula has a maximum at VIN = 2VOUT, where I RMS = I OUT/2. This simple worst case condition is commonly used for design because even significant deviations do not offer much relief. 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 + 8fCOUT ⎥⎦ ⎣ 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. A sudden inrush of current through the long wires can potentially cause a voltage spike at VIN large enough to damage the part. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 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 RT7247B, 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) 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 7, 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 7.a), θJA is 75°C/W. Adding copper area of pad under the SOP-8 (Exposed Pad) (Figure 7.b) reduces the θJA to 64°C/W. Even further, increasing the copper area of pad to 70mm2 (Figure 7.e) reduces the θJA to 49°C/W. is a registered trademark of Richtek Technology Corporation. DS7247B-01 September 2012 RT7247B The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 8 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power dissipation allowed. (a) Copper Area = (2.3 x 2.3) mm2, θJA = 75°C/W 2.2 Four-Layer PCB Power Dissipation (W) 2.0 1.8 Copper Area 70mm2 50mm2 30mm2 10mm2 Min.Layout 1.6 1.4 1.2 1.0 0.8 0.6 (b) Copper Area = 10mm2, θJA = 64°C/W 0.4 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 8. Derating Curve of Maximum Power Dissipation (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 7. Thermal Resistance vs. Copper Area Layout Design Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7247B-01 September 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT7247B Layout Consideration Follow the PCB layout guidelines for optimal performance of the RT7247B. ` 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). ` SW node is with high frequency voltage swing and should be kept at small area. Keep analog components VIN GND away from the SW node to prevent stray capacitive noise pick-up. ` Connect feedback network behind the output capacitors. Keep the loop area small. Place the feedback components near the RT7247B. ` An example of PCB layout guide is shown in Figure 9 for reference. SW GND VIN CBOOT Input capacitor must be placed as close to the IC as possible. BOOT L VOUT REN CSS CIN VIN 2 SW 3 GND 4 GND CC 8 SS 7 EN 6 COMP 5 FB 9 The feedback components must be connected as close to the device as possible. CP RC R1 R2 COUT VOUT GND SW node is with high frequency voltage swing and should be kept at small area. Keep analog components away from the SW node to prevent stray capacitive noise pick-up Figure 9. PCB Layout Guide 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. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS7247B-01 September 2012 RT7247B 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. DS7247B-01 September 2012 www.richtek.com 15