® RT7263B 3A, 21V 500kHz Synchronous Step-Down Converter General Description Features The RT7263B is a synchronous step-down regulator with an internal power MOSFET. It achieves 3A of continuous output current over a wide input supply range with excellent load and line regulation. Current mode operation provides fast transient response and eases loop stabilization. z Wide Input Range : 4.5V to 21V z Adjustable Output from 0.603V to 15V 3A Output Current 120mΩ Ω/40mΩ Ω Internal Power MOSFET Switch Internal Compensation Minimizes External Parts 500kHz Fixed Switching Frequency Synchronized External Clock from 300kHz to 2MHz Adjustable Soft-Start Cycle-by-Cycle Over Current Limit Thermal Shutdown Protection Small 14-Lead WDFN Package RoHS Compliant and Halogen Free z z z z Fault condition protection includes cycle-by-cycle current limiting and thermal shutdown. An adjustable soft-start reduces the stress on the input source at startup. z z z The RT7263B requires a minimal number of readily available external components, providing a compact solution. z z z Ordering Information Applications RT7263B z Package Type QW : WDFN-14L 4x3 (W-Type) z z Lead Plating System Z : ECO (Ecological Element with Halogen Free and Pb free) z Distributive Power Systems Battery Charger DSL Modems Pre-Regulator for Linear Regulators Marking Information Note : 10 : Product Code Richtek products are : ` 10 YM DNN RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. ` YMDNN : Date Code Suitable for use in SnPb or Pb-free soldering processes. Simplified Application Circuit VIN VIN CIN BOOT RT7263B CBOOT L VCC SW VOUT CC RT SYNC ON/OFF SYNC EN AGND Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7263B-01 September 2012 R1 COUT FB CSS SS R2 GND is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT7263B Pin Configurations (TOP VIEW) VIN SW SW SW SW BOOT SYNC 14 13 1 2 3 4 5 6 7 GND 15 12 11 10 9 8 AGND GND GND VCC SS EN FB WDFN-14L 4x3 Function Pin Description Pin No. Pin Name Pin Function 1 VIN Power Input. VIN supplies the power to the IC, as well as the step-down converter switches. Drive VIN with a 4.5V to 21V power source. Bypass VIN to GND with a suitably large capacitor to eliminate noise on the input to the IC. 2, 3, 4, 5 SW Switch Node. SW is the switching node that supplies power to the output. Connect the output LC filter from SW to the output load. Note that a capacitor is required from SW to BOOT to power the high side switch. 6 BOOT Bootstrap for High Side Gate Driver. Connect a 100nF or greater capacitor from SW to BOOT to power the high side switch driver. 7 SYNC External Frequency Synchronization Input. Connect an external clock on this pin changes the switching frequency. 8 FB Feedback Input. FB senses the output voltage via an external resistive voltage divider. The feedback reference voltage is 0.603V typically. 9 EN Enable Control Input. Floating this pin or connecting this pin to logic high will enable the device and connecting this pin to GND will disable the device. 10 SS Soft-Start Control Input. Connect a capacitor from SS to GND to set the soft-start period. 11 VCC Bias Supply. Decouple with 0.1μF to 0.22μF capacitor between this pin and GND. 12, 13, GND 15 (Exposed Pad) Ground. The exposed pad must be soldered to a large PCB and connected to GND for maximum power dissipation. 14 AGND Analog Ground. Connect this pin to the system ground in PCB layout. Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS7263B-01 September 2012 RT7263B Function Block Diagram VIN VCC EN Current Sense Amplifier - Ramp Generator + Regulator BOOT S Oscillator Q + SYNC OC Limit Clamp Reference FB 10µA SS Driver R PWM Comparator SW Error Amplifier + + - GND 400k 30pF 1pF Operation The RT7263B 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 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 150kHz for low power consumption. Internal Regulator The regulator provides low voltage power to supply the internal control circuits and the bootstrap power for high side gate driver. Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7263B-01 September 2012 Enable 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 be less than 1μA. 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 4ms. 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 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 30°C, the converter will automatically resume switching. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT7263B Absolute Maximum Ratings z z z z z z z z z z (Note 1) Supply Input Voltage, VIN ---------------------------------------------------------------------------------Switch Voltage, SW ----------------------------------------------------------------------------------------Boot Voltage, BOOT ----------------------------------------------------------------------------------------Other Pins -----------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WDFN-14L 4x3 -----------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WDFN-14L 4x3, θJA -----------------------------------------------------------------------------------------WDFN-14L 4x3, θJC -----------------------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) -----------------------------------------------------------------Storage Temperature Range ------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) --------------------------------------------------------------------------------- Recommended Operating Conditions z z z −0.3V to 26V −0.3V to (VIN + 0.3V) (SW − 0.3V) to (SW + 6V) −0.3V to 6V 1.667W 60°C/W 7°C/W 150°C 260°C −65°C to 150°C 2kV (Note 4) Supply Input Voltage, VIN ---------------------------------------------------------------------------------- 4.5V to 21V 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 Current ISHDN VEN = 0 -- 0 1 μA Quiescent Current IQ VEN = 2V, VFB = 1V -- 0.7 -- mA Upper Switch On Resistance R DS(ON)1 -- 120 -- mΩ Lower Switch On Resistance R DS(ON)2 -- 40 -- mΩ Switch Leakage ILEAK VEN = 0V, VSW = 0V or 12V -- 0 10 μA Current Limit ILIMIT VBOOT − VSW = 4.8V 5.4 6.5 -- A Oscillator Frequency fSW VFB = 0.75V 425 500 575 kHz VFB = 0V -- 150 -- kHz VFB = 0.8V -- 90 -- % -- 100 -- ns Short Circuit Frequency Maximum Duty Cycle D MAX Minimum On Time tON Feedback Voltage VFB Feedback Current IFB -- 10 50 Logic-High VIH 2 -- 5.5 Logic-Low VIL -- -- 0.4 VEN = 2V -- 1 -- VEN = 0V -- 0 -- EN Voltage Enable Current 4.5V ≤ VIN ≤ 21V Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 0.593 0.603 0.613 V nA V μA is a registered trademark of Richtek Technology Corporation. DS7263B-01 September 2012 RT7263B Parameter Symbol Test Conditions Min Typ Max Unit SYNC Threshold Logic-High Voltage Logic-Low VSYNCH 1.8 -- -- VSYNCL -- -- 0.4 SYNC Frequency Range fSYNC 0.3 -- 2 MHz SYNC Input Current ISYNC VSYNC = 6V -- 1.5 2.5 μA Under Voltage Lockout Threshold VUVLO VIN Rising 3.8 4 4.2 V Under Voltage Lockout Threshold Hysteresis ΔVUVLO -- 400 -- mV -- 5 -- V ICC = 5mA -- 5 -- % CSS = 47nF -- 4.7 -- ms VCC Regulator VCC Load Regulation Soft-Start Period tSS Thermal Shutdown Threshold TSD -- 150 -- Thermal Shutdown Hysteresis ΔTSD -- 30 -- V °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. DS7263B-01 September 2012 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT7263B Typical Application Circuit 1 VIN BOOT VIN CIN 22µF 6 CBOOT 100nF RT7263B 11 VCC SW CC 0.1µF 2, 3, 4, 5 FB 8 SYNC ON/OFF 7 SYNC SS 10 9 EN L VOUT R1 RT COUT CSS 47nF R2 GND 12, 13, 15 (Exposed Pad) AGND 14 Table 1. Recommended Components Selection VOUT (V) R1 (kΩ) R2 (kΩ) RT (kΩ) L (μH) COUT (μF) 5 75 10.23 0 4.7 22 x 2 3.3 75 16.67 0 3.6 22 x 2 2.5 75 23.68 0 3.6 22 x 2 1.8 5 2.5 24 2 22 x 2 1.5 5 3.33 27 2 22 x 2 1.2 5 5 36 2 22 x 2 1.05 5 6.67 39 1.5 22 x 2 Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS7263B-01 September 2012 RT7263B Typical Operating Characteristics Efficiency vs. Output Current Reference Voltage vs. Input Voltage 100 0.620 90 0.615 70 Reference Voltage (V) Efficiency (%) 80 VIN = 12V VIN = 21V 60 50 40 30 20 0.610 0.605 0.600 0.595 0.590 0.585 10 VOUT = 1.2V, IOUT = 0A to 3A 0 0.580 0 0.5 1 1.5 2 2.5 3 4 6 8 10 14 16 18 20 22 Input Voltage (V) Output Current (A) Output Voltage vs. Output Current Reference Voltage vs. Temperature 0.64 1.24 0.63 1.23 0.62 1.22 Output Voltage (V) Reference Voltage (V) 12 0.61 0.60 0.59 0.58 1.21 1.20 VIN = 21V VIN = 12V 1.19 1.18 0.57 1.17 0.56 1.16 VOUT = 1.2V, IOUT = 0A to 3A -50 -25 0 25 50 75 100 125 0 0.5 1 Temperature (°C) Switching Frequency vs. Input Voltage 2 2.5 3 Switching Frequency vs. Temperature 550 650 Switching Frequency (kHz)1 Switching Frequency (kHz)1 1.5 Output Current (A) 525 500 475 450 425 600 550 500 450 400 350 VOUT = 1.2V 400 VIN = 12V, VOUT = 1.2V 300 4 6 8 10 12 14 16 18 20 Input Voltage (V) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7263B-01 September 2012 22 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT7263B Current Limit vs. Temperature 12 10 10 Current Limit (A) Current Limit (A) Current Limit vs. Input Voltage 12 8 6 4 8 6 4 2 2 0 0 VIN = 12V, VOUT = 1.2V 4 6 8 10 12 14 16 18 20 22 -50 0 25 50 75 100 Input Voltage (V) Temperature (°C) Load Transient Response Load Transient Response VOUT (500mV/Div) VOUT (200mV/Div) IOUT (1A/Div) IOUT (1A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 0A to 3A Time (100μs/Div) Output Ripple Voltage Output Ripple Voltage VOUT (50mV/Div) VSW (10V/Div) VSW (10V/Div) IL (1A/Div) IL (2A/Div) VIN = 12V, IOUT = 3A VIN = 12V, IOUT = 1A Time (1μs/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. 125 VIN = 12V, VOUT = 1.2V, IOUT = 1A to 3A Time (100μs/Div) VOUT (50mV/Div) www.richtek.com 8 -25 Time (1μs/Div) is a registered trademark of Richtek Technology Corporation. DS7263B-01 September 2012 RT7263B Power On from VIN Power Off from VIN VIN (10V/Div) VIN (10V/Div) VOUT (1V/Div) VSW (20V/Div) VOUT (1V/Div) VSW (20V/Div) IL (5A/Div) IL (5A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 3A Time (5ms/Div) Time (25ms/Div) Power On from EN Power Off from EN VEN (5V/Div) VEN (5V/Div) VOUT (1V/Div) VSW (20V/Div) VOUT (1V/Div) VSW (20V/Div) IL (5A/Div) IL (5A/Div) VIN = 12V, VOUT = 1.2V, IOUT = 3A Time (2.5ms/Div) Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7263B-01 VIN = 12V, VOUT = 1.2V, IOUT = 3A September 2012 VIN = 12V, VOUT = 1.2V, IOUT = 3A Time (50μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT7263B Application Information The IC is a synchronous high voltage step-down converter that can support the input voltage range from 4.5V to 21V and the output current can be up to 3A. Output Voltage Setting The output voltage is set by an external resistive divider according to the following equation : VOUT = VFB ⎛⎜ 1+ R1 ⎞⎟ ⎝ R2 ⎠ where VFB is the feedback reference voltage 0.603V (typ.). The resistive divider allows the FB pin to sense a fraction of the output voltage as shown in Figure 1. VOUT R1 FB RT7263B R2 Soft-Start The IC contains an external soft-start clamp that gradually raises the output voltage. The soft-start timing is programmed by the external capacitor between SS pin and GND. The chip provides an internal 10μA charge current for the external capacitor. If 47nF capacitor is used to set the soft-start, the period will be 4.7ms (typ.). Under Voltage Lockout Threshold The IC includes an input Under Voltage Lockout Protection (UVLO). If the input voltage exceeds the UVLO rising threshold voltage (4.2V), the converter resets and prepares the PWM for operation. If the input voltage falls below the UVLO falling threshold voltage (3.8V) during normal operation, the device stops switching. The UVLO rising and falling threshold voltage includes a hysteresis to prevent noise caused reset. GND Chip Enable Operation Figure 1. Output Voltage Setting External Bootstrap Diode Connect a 100nF low ESR ceramic capacitor between the BOOT pin and SW pin as shown in Figure 2. 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 IC. Note that the external boot voltage must be lower than 5.5V. The EN pin is the chip enable input. Pulling the EN pin low (<0.4V) will shutdown the device. During shutdown mode, the RT7263B quiescent current drops to lower than 1μA. Driving the EN pin high (2V < EN < 5.5V) 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 CEN EN RT7263B GND Figure 3. Enable Timing Control 5V BOOT RT7263B 100nF SW An external MOSFET can be added to implement digital control on the EN pin, as shown in Figure 4. In this case, a 100kΩ pull-up resistor, REN, is connected between VIN pin and the EN pin. MOSFET Q1 will be under logic control to pull down the EN pin. Figure 2. External Bootstrap Diode Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS7263B-01 September 2012 RT7263B VIN REN 100k 2ms EN RT7263B Q1 EN 10µs VIN EN/SYNC GND VCC Figure 4. Digital Enable Control Circuit The chip starts to operate when VIN rises to 4.2V (UVLO threshold). During the VIN rising period, if an 8V output voltage is set, VIN is lower than the VOUT target value and it may cause the chip to shut down. To prevent this situation, a resistive voltage divider can be placed between the input voltage and ground and connected to the EN pin to adjust enable threshold, as shown in Figure 5. For example, the setting VOUT is 8V and VIN is from 0V to 12V, when VIN is higher than 10V, the chip is triggered to enable the converter. Assume REN1 = 50kΩ. Then, REN2 = (REN1 x VIH(MIN) ) (VIN_S − VIH(MIN) ) where VIH(MIN) is the minimum threshold of enable rising (2V) and VIN_S is the target turn on input voltage (10V in this example). According to the equation, the suggested resistor R EN2 is 12.5kΩ. VIN REN1 EN REN2 RT7263B VOUT CLK External CLK Figure 6. Startup Sequence Using External Sync Clock Figure 6 shows the synchronization operation in startup period. When the EN/SYNC is triggered by an external clock, the RT7263B enters soft-start phase and the output voltage starts to rise. During the soft-start phase region, the oscillation frequency will be proportional to the feedback voltage until it is higher than 0.7V. With higher VFB, the switching frequency is relatively higher. After startup period about 2ms, the IC operates with the same frequency as the external clock. Output Under Voltage Protection (Hiccup Mode) For the IC, Hiccup Mode of Under Voltage Protection (UVP) is provided. When the FB voltage drops below half of the feedback reference voltage, VFB, the UVP function will be triggered and the IC will shut down for a period of time and then recover automatically. The Hiccup Mode of UVP can reduce input current in short-circuit conditions. GND Inductor Selection Figure 5. Resistor Divider for Lockout Threshold Setting Operating Frequency and Synchronization The internal oscillator runs at 500kHz (typ.) when the EN/ SYNC pin is at logic-high level (>2V). If the EN pin is pulled to low-level for 10μs above, the IC will shut down. The RT7263B can be synchronized with an external clock ranging from 300kHz to 2MHz applied to the EN/SYNC pin. The external clock duty cycle must be from 30% to 90%. Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7263B-01 September 2012 For a given input and output voltage, the inductor value and operating frequency determine the ripple current. 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. Highest efficiency operation is achieved by reducing ripple current at low frequency, but it requires a large inductor to attain this goal. is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT7263B 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 a specified maximum, the inductor value should be chosen according to the following equation : ⎡ VOUT ⎤ ⎡ VOUT ⎤ L =⎢ × ⎢1 − ⎥ ⎥ ⎣ f × ΔIL(MAX) ⎦ ⎣ VIN(MAX) ⎦ Input and Output Capacitors Selection 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 and it is highly recommended to keep inductor value as close as possible to the recommended inductor values for each VOUT as shown in Table 1. 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. The input capacitance, C IN, is needed to filter the trapezoidal current at the source of the high side MOSFET. To prevent large ripple current, a low ESR input capacitor sized for the maximum RMS current should be used. The RMS current is given by : V IRMS = IOUT(MAX) OUT VIN VIN −1 VOUT Choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet size or height requirements in the design. For the input capacitor, one 22μF low ESR ceramic capacitors are recommended. For the recommended capacitor, please refer to table 3 for more detail. Table 2. Suggested Inductors for Typical Application Circuit Component Supplier Series Dimensions (mm) TDK VLF10045 10 x 9.7 x 4.5 TDK SLF12565 12.5 x 12.5 x 6.5 TAIYO YUDEN NR8040 8x8x4 Table 3. Suggested Capacitors for CIN and COUT Location Component Supplier Part No. Capacitance (μF) Case Size CIN MURATA GRM32ER71C226M 22 1210 CIN TDK C3225X5R1C226M 22 1210 COUT MURATA GRM31CR60J476M 47 1206 COUT TDK C3225X5R0J476M 47 1210 COUT MURATA GRM32ER71C226M 22 1210 COUT TDK C3225X5R1C226M 22 1210 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. The output ripple, ΔVOUT, is determined by : 1 ⎤ ΔVOUT ≤ ΔIL ⎡⎢ESR + 8fCOUT ⎥⎦ ⎣ Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 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. is a registered trademark of Richtek Technology Corporation. DS7263B-01 September 2012 RT7263B Thermal Shutdown Maximum Power Dissipation (W)1 1.80 Thermal shutdown in implemented to prevent the chip from operating at excessively high temperatures. When the junction temperature is higher than 150°C, the chip is shut down the switching operation. The chip is automatically re-enabled when the junction temperature cools down by approximately 30°C. Thermal Considerations For continuous operation, do not exceed absolute maximum junction temperature. The maximum power dissipation depends on the thermal resistance of the IC package, PCB layout, rate of surrounding airflow, and difference between junction and ambient temperature. The maximum power dissipation can be calculated by the following formula : PD(MAX) = (TJ(MAX) − TA) / θJA where TJ(MAX) is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction to ambient thermal resistance. For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For WDFN-14L 4x3 package, the thermal resistance, θJA, is 60°C/W on a standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by the following formula : Copyright © 2012 Richtek Technology Corporation. All rights reserved. DS7263B-01 September 2012 1.50 1.20 0.90 0.60 0.30 0.00 0 25 50 75 100 125 Ambient Temperature (°C) Figure 7. Derating Curve of Maximum Power Dissipation Layout Considerations Follow the PCB layout guidelines for optimal performance of the IC. ` 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 away from the SW node to prevent stray capacitive noise pickup. ` Connect feedback network behind the output capacitors. Keep the loop area small. Place the feedback components near the IC. ` Connect all analog grounds to a common 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 8 for reference. PD(MAX) = (125°C − 25°C) / (60°C/W) = 1.667W for WDFN-14L 4x3 package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curve in Figure 7 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Four-Layer PCB is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT7263B SW should be connected to inductor by wide and short trace and keep sensitive components away from this trace. GND CIN VIN SW SW SW CBOOT SW BOOT SYNC 1 14 2 13 3 4 5 6 GND 15 7 L VOUT COUT 12 11 10 9 8 AGND GND CSS GND VCC SS EN FB RT R2 R1 Place the feedback components as close to the IC as possible. VOUT GND Place the input and output capacitors as close to the IC as possible. Figure 8. PCB Layout Guide Copyright © 2012 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 is a registered trademark of Richtek Technology Corporation. DS7263B-01 September 2012 RT7263B Outline Dimension 2 1 2 1 DETAIL A Pin #1 ID and Tie Bar Mark Options Note : The configuration of the Pin #1 identifier is optional, but must be located within the zone indicated. Dimensions In Millimeters Dimensions In Inches Symbol Min Max Min Max A 0.700 0.800 0.028 0.031 A1 0.000 0.050 0.000 0.002 A3 0.175 0.250 0.007 0.010 b 0.180 0.300 0.007 0.012 D 3.900 4.100 0.154 0.161 D2 3.250 3.350 0.128 0.132 E 2.900 3.100 0.114 0.122 E2 1.650 1.750 0.065 0.069 e L 0.500 0.350 0.020 0.450 0.014 0.018 W-Type 14L DFN 4x3 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. DS7263B-01 September 2012 www.richtek.com 15