® RT8088A 2.7MHz 3A Step-Down Converter with I2C Interface General Description Features The RT8088A is a full featured 5.5V, 3A, Constant-OnTime (COT) synchronous step-down converter with two integrated MOSFETs. The current mode COT operation with internal compensation allows the transient response to be optimized over a wide range of loads and output capacitors to efficiently reduce external component count. The RT8088A provides up to 3MHz switching frequency to minimize the size of output inductor and capacitors. The RT8088A is available in the WL-CSP-15B 1.31x2.11 (BSC) package. z 2.5V to 5.5V Input Voltage Range z Current Mode COT Control Loop Design Fast Transient Response Internal 48mΩ Ω and 22mΩ Ω Synchronous Rectifier Highly Accurate VOUT Regulation Over Load/Line Range Robust Loop Stability with Low-ESR COUT RoHS Compliant and Halogen Free z z z z z Applications z Ordering Information z RT8088A Package Type WSC : WL-CSP-15B 1.31x2.11 (BSC) z Distributed Power Systems Enterprise Servers, Ethernet Switches & Routers, and Global Storage Equipment Telecom & Industrial Equipment Pin Configurations Note : Richtek products are : ` (TOP VIEW) RoHS compliant and compatible with the current requirePVIN ments of IPC/JEDEC J-STD-020. ` A1 A2 A3 PGND B3 PGND C3 PGND D3 SDA E3 FB LX Suitable for use in SnPb or Pb-free soldering processes. PVIN B1 B2 LX PVIN C1 Marking Information AVIN D1 1J : Product Code 1JW C2 PGND D2 EN AGND W : Date Code E1 E2 SCL WL-CSP-15B 1.31x2.11 (BSC) Simplified Application Circuit RT8088A VIN … Enable 2 I C Control Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8088A-00 October 2013 PVDD LX AVDD FB EN PGND SDA SCL AGND VOUT is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8088A Functional Pin Description Pin No. A1, B1, C1 A2, B2 Pin Name Pin Function PVIN Input Supply Voltage, 2.5V to 5.5V. LX Switch Node. The Source of the internal high-side power MOSFET, and Drain of the internal low-side (synchronous) rectifier MOSFET. A3, B3, C2, C3 PGND Power Ground. D1 AVIN Analog Circuit Input Supply Voltage. D2 EN Enable Control Input. Pull high to enable. D3 SDA I C Data Signal. E1 AGND Analog Ground Should be Electrically Connected to GND Close to the Device. E2 SCL I C Clock Signal. E3 FB Feedback Voltage Input. 2 2 Function Block Diagram EN UVLO Shutdown Control OTP FB AVIN TON Error Amplifier + + 0.8V Comparator + - Logic Control LX PVIN Driver LX RC VREF SDA SCL CCOMP 2 I C Control Current Limit Detector Current Sense AZC Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 LX PGND LX AGND is a registered trademark of Richtek Technology Corporation. DS8088A-00 October 2013 RT8088A Operation The RT8088A is a low voltage synchronous step-down converter that can support the input voltage range from 2.5V to 5.5V and the output current can be up to 3A. The RT8088A uses a constant on-time, current mode architecture. In steady-state operation, the high-side PMOSFET is turned on when the current feedback reaches COMP level which is the amplified difference between the reference voltage and the feedback voltage. The on-time of high-side P-MOSFET is determined by on-time generator which is a function of input and output voltage. After on-time expires, high-side MOSFET is turned off and low-side MOSFET is turned on. Until the low-side current sensing signal reaches the COMP, the high-side MOSFET is turned on again. In this manner, the converter regulates the output voltage and keeps the frequency constant. The RT8088A reduces the external component count by integrating the boot recharge MOSFET. The error amplifier EA adjusts COMP voltage by comparing the output voltage with the internal I2C set reference voltage. When the load increases, it causes a drop in the output relative to the reference, then the COMP voltage rises to allow higher inductor current to match the load current. PWM Frequency and Adaptive On-Time Control The on-time can be roughly estimated by the equation : V 1 TON = OUT × where fSW is nominal 3MHz V f IN SW Auto-Zero Current Detector The auto-zero current detector circuit senses the LX waveform to adjust the zero current threshold voltage. When the current of low-side MOSFET decreases to the zero current threshold, the low-side MOSFET turns off to prevent negative inductor current. In this way, the zero current threshold can adjust for different condition to get better efficiency. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8088A-00 October 2013 Under-Voltage Lockout (UVLO) The UVLO continuously monitors the VCC voltage to make sure the device works properly. When the VCC is high enough to reach the UVLO high threshold voltage, the step-down converter softly starts or pre-bias to its regulated output voltage. When the VCC decreases to its UVLO low threshold voltage, the device will shut down. Power Good When the output voltage is higher than PGOOD rising threshold, the PGOOD flag is high. Output Under-Voltage Protection (UVP) When the output voltage is lower than 0.4V after softstart, the UVP is triggered. The system will be latched and the output voltage will no longer be regulated during UVP latched state. Re-start input voltage or EN pin can unlatch the protection state. Using I2C to shutdown the system and then re-enable it will also unlatch UVP function. Over-Current Protection (OCP) The RT8088A senses the current signal when the lowside MOSFET turns on. As a result, The OCP is cycleby-cycle limit. If the OCP occurs, the converter holds off the next on pulse until inductor current drops below the OCP limit. Soft-Start An internal current source charges an internal capacitor to build the soft-start ramp voltage. The typical soft start time is 150μs. Over-Temperature Protection (OTP) The RT8088A has an over-temperature protection. When the device triggers the OTP, the system will be latched and the output voltage will no longer be regulated during OTP latched state. Re-start input voltage or EN pin can unlatch the protection state. Using I2C to shutdown the system and then re-enable it will also unlatch UVP function. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8088A Absolute Maximum Ratings z z z z z z z z (Note 1) Supply Input Voltage, VIN ---------------------------------------------------------------------------------------Other Pins -----------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C WL-CSP-15B 1.31x2.11 (BSC) --------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WL-CSP-15B 1.31x2.11 (BSC), θJA ---------------------------------------------------------------------------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 6.5V −0.3V to (VIN + 0.3V) 2W 49.8°C/W 150°C 260°C −65°C to 150°C 2kV (Note 4) Supply Input Voltage, VIN ---------------------------------------------------------------------------------------- 2.5V to 5.5V Junction Temperature Range ------------------------------------------------------------------------------------- −40°C to 125°C Ambient Temperature Range ------------------------------------------------------------------------------------- −40°C to 85°C Electrical Characteristics (VIN = 3.7V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit Under-Voltage Lockout Threshold VUVLO VCC Rising -- 2.35 -- V Shutdown Supply Current ISHDN EN = 0V -- 1 5 μA Quiescent Current IQ Active, VSENSE = 0.9V, No Switching -- 75 100 μA Voltage Reference VREF At any set point, with a load from 0 to 3A and over input voltage range −2 -- 2 % Soft-Start Time tSS -- -- 150 μs Enable Input Voltage Switch On-Resistance Logic-High VEN_H Rising 1.05 -- -- Logic-Low VEN_L Falling -- -- 0.4 High-Side RONH -- 48 -- Low-Side RONL -- 22 -- -- 3.9 -- A Valley Current, IPEAK [1:0] = 11 V mΩ Current Limit Threshold ICL Thermal Shutdown Threshold TS -- 150 -- °C Switching Frequency fOSC -- 2.7 -- MHz Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8088A-00 October 2013 RT8088A Parameter Symbol Test Conditions Default VOUT = 1.225V (Register 1100100) Min Typ Max Unit 7 -- -- Bits Resolution RES DAC Step Size VDAC -- 6.25 -- mV Minimum VOUT VDACMIN -- 600 -- mV EN, SDA and SCL High DHIGH 1.05 -- -- V EN, SDA and SCL Low DLOW -- -- 0.4 V EN, SDA and SCL Current DCURRENT -- -- 0.1 mA 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. 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. DS8088A-00 October 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8088A Typical Application Circuit VIN Remote 47µF … A1, B1, C1 4.7µF Enable 2 I C Control D1 AVDD D2 EN D3 SDA E2 SCL Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 RT8088A PVDD LX FB PGND A2, B2 0.33µH E3 VOUT 22µF A3, B3, C2, C3 AGND E1 is a registered trademark of Richtek Technology Corporation. DS8088A-00 October 2013 RT8088A Typical Operating Characteristics Efficiency vs. Output Current Output Voltage vs. Input Voltage 100 1.26 90 1.25 Efficiency (%) 70 Output Voltage (V) 80 VIN = 3V VIN = 3.7V VIN = 4.2V 60 50 40 30 1.24 1.23 IOUT = 0A IOUT = 3A IOUT = 1A 1.22 1.21 1.2 20 1.19 10 VOUT = 1.225V, L = 0.33μH 0 0.001 VOUT = 1.225V 1.18 0.01 0.1 1 3 10 3.5 4 Output Current (A) 5 1.25 1.25 1.24 1.24 1.23 1.22 VIN = 5.5V VIN = 3.7V VIN = 3V 1.20 1.19 1.23 VIN = 4.2V VIN = 3.7V VIN = 3V 1.22 1.21 1.20 1.19 VOUT = 1.225V IOUT = 1A 1.18 1.18 -50 -25 0 25 50 75 100 125 0 0.5 1 1.5 2 2.5 3 Output Current (A) Temperature (°C) Frequency vs. Input Voltage Frequency vs. Temperature 3.0 3.0 2.9 2.9 Frequency (MHz) Frequency (MHz) 5.5 Output Voltage vs. Output Current 1.26 Output Voltage (V) Output Voltage (V) Output Voltage vs. Temperature 1.26 1.21 4.5 Input Voltage (V) 2.8 2.7 2.6 2.5 2.4 2.8 2.7 2.6 2.5 2.4 VOUT = 1.225V, IOUT = 1A 2.3 VIN = 3.7V, VOUT = 1.225V, IOUT = 1A 2.3 2.5 3 3.5 4 4.5 5 Input Voltage (V) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8088A-00 October 2013 5.5 -50 -25 0 25 50 75 100 125 Temperature (°C) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8088A Output Current Limit vs. Input Voltage UVLO Voltage vs. Temperature 5.0 2.50 2.40 4.0 UVLO Voltage (V) Output Current Limit (A) 2.45 4.5 IPEAK <1:0>=11 3.5 IPEAK <1:0>=10 3.0 IPEAK <1:0>=01 2.5 2.35 Rising 2.30 2.25 2.20 2.15 Falling 2.10 2.05 VOUT = 1.225V 2.0 VOUT = 1.225V, IOUT = 0A 2.00 3 3.5 4 4.5 5 5.5 -50 -25 0 25 50 75 100 125 Temperature (°C) Input Voltage (V) EN Threshold vs. Input Voltage EN Threshold vs. Temperature 1.0 1.4 1.3 1.2 EN Threshold (V) EN Threshold (V) 0.9 0.8 Rising 0.7 0.6 1.1 1.0 0.9 0.8 Rising 0.7 0.6 Falling VOUT = 1.225V, IOUT = 0A 0.5 Falling 0.5 VIN = 3.7V, VOUT = 1.225V, IOUT = 0A 0.4 2.5 3 3.5 4 4.5 5 5.5 -50 0 25 50 75 100 Temperature (°C) Load Transient Response Load Transient Response VOUT (20mV/Div) VOUT (20mV/Div) IOUT (2A/Div) IOUT (2A/Div) VIN = 3.7V, VOUT = 1.225V, IOUT = 10mA to 3A, L = 0.33μH Time (50μs/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 -25 Input Voltage (V) 125 VIN = 3.7V, VOUT = 1.225V, IOUT = 1A to 3A, L = 0.33μH Time (50μs/Div) is a registered trademark of Richtek Technology Corporation. DS8088A-00 October 2013 RT8088A Output Ripple Voltage Output Ripple Voltage VIN = 3.7V, VOUT = 1.225V, IOUT = 10mA, L = 0.33μH VIN = 3.7V, VOUT = 1.225V, IOUT = 1A, L = 0.33μH VOUT (5mV/Div) VOUT (10mV/Div) VLX (2V/Div) VLX (2V/Div) Time (10μs/Div) Time (250ns/Div) Power On from VIN Power Off from VIN VIN = 3.7V, VOUT = 1.225V, IOUT = 3A VIN = 3.7V, VOUT = 1.225V, IOUT = 3A VIN (5V/Div) VIN (5V/Div) VLX (5V/Div) VLX (5V/Div) VOUT (1V/Div) VOUT (1V/Div) I IN (2A/Div) I IN (2A/Div) Time (2.5ms/Div) Time (5ms/Div) Power On from EN Power Off from EN VIN = 3.7V, VOUT = 1.225V, IOUT = 3A VEN (2V/Div) VEN (2V/Div) VOUT (1V/Div) VOUT (1V/Div) VLX (5V/Div) VLX (5V/Div) I IN (2A/Div) I IN (2A/Div) VIN = 3.7V, VOUT = 1.225V, IOUT = 3A Time (25μs/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8088A-00 October 2013 Time (25μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8088A Application Information The basic RT8088A application circuit is shown in Typical Application Circuit. External component selection is determined by the maximum load current and begins with the selection of the inductor value and operating frequency followed by CIN and COUT. 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, as shown in equation below : ⎤ ⎡V ⎤ ⎡ V ΔIL = ⎢ OUT ⎥ x ⎢1− OUT ⎥ VIN ⎦ ⎣ fxL ⎦ ⎣ where f is the operating frequency and L is the inductance. Having a lower ripple current reduces not only the ESR losses in the output capacitors, but also the output voltage ripple. Higher operating frequency combined with smaller ripple current is necessary to achieve high efficiency. Thus, a large inductor is required to attain this goal. The largest ripple current occurs at the highest VIN. To guarantee that the ripple current stays below the specified ΔIL(MAX), the inductor value should be chosen according to the following equation : ⎡ VOUT ⎤ ⎡ ⎤ V L=⎢ ⎥ x ⎢1− OUT ⎥ ⎢⎣ f x ΔIL(MAX) ⎥⎦ ⎢⎣ VIN(MAX) ⎥⎦ The inductor's current rating (defined by a temperature rise from 25°C ambient to 40°C) should be greater than the maximum load current and its saturation current should be greater than the short-circuit peak current limit. Refer to Table 1 for the suggested inductor selection. Table 1. Suggested Inductors for Typical Application Circuit Component Supplier CYNTEC Part Number PIFE20161BR33MS-39 Dimensions (mm) An input capacitor, C IN, is needed to filter out 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 : IRMS = IOUT(MAX) VOUT VIN VIN −1 VOUT This formula has a maximum at VIN = 2VOUT, where IRMS = IOUT(MAX)/2. This simple worst-case condition is commonly used for design. Choose a capacitor rated at a higher temperature than required. Several capacitors may also be paralleled to meet the size or height requirements of the design. Ceramic capacitors have high ripple current, high voltage rating and low ESR, which makes them ideal for switching regulator applications. However, they can also have a high voltage coefficient and audible piezoelectric effects. The high Q of ceramic capacitors with trace inductance can lead to significant ringing. 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. Thus, care must be taken to select a suitable input capacitor. The selection of COUT is determined by the required ESR to minimize output 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 voltage ripple, ΔVOUT, is determined by : ⎡ ⎤ 1 ΔVOUT ≤ ΔIL ⎢ESR + ⎥ 8fOSCCOUT ⎦ ⎣ 2.0 X 1.6 X 1.2 Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 Input and Output Capacitor Selection is a registered trademark of Richtek Technology Corporation. DS8088A-00 October 2013 RT8088A where fOSC is the switching frequency and ΔIL is the inductor ripple current. The output voltage 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. 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. Nevertheless, high value, low 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. I2C Interface Function RT8088A can be used by I2C interface to select Vout voltage level, peak current limit level, thermal warning temperature level, PWM control mode, and so on. The register of each function can be found from the following register map and it also explains how to use these function. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8088A-00 October 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT8088A I2C Interface The RT8088A I2C slave address = 7'b0011100. I2C Register Map Register b[7] Register Address Name (MSB) b[6] b[5] b[4] b[3] b[2] SEN_ TSD SEN_ TWARN SEN_ TPREW Default 0 0 0 0 0 0 0 0 Read/Write R R R R R R R R b[2] b[1] b[0] (LSB) RESV SEN_PG SEN_TSD 0 : Junction temperature below thermal shutdown (150°C) limit 1 : Junction temperature above thermal shutdown (150°C) limit SEN_TWARN 0 : Junction temperature below thermal shutdown (135°C) limit 1 : Junction temperature above thermal shutdown (135°C) limit SEN_TPREW 0 : Junction temperature below thermal shutdown (105°C) limit 1 : Junction temperature above thermal shutdown (105°C) limit RESV Reserved bits 0 : DCDC output voltage below target 1 : DCDC output voltage within nominal range SEN_PG Register b[7] Register Address Name (MSB) b[6] b[5] Meaning PRODUCT_ID 0 0 1 0 1 0 1 Read/Write R R R R R R R R b[5] b[4] b[3] b[2] b[1] b[0] (LSB) PRODUCT_ID b[7] (MSB) b[6] Meaning REVISION_ID Default 0 0 0 0 0 0 0 1 Read/Write R R R R R R R R b[6] b[5] b[4] b[3] b[2] b[1] b[0] (LSB) REVISION_ID Register Register Address Name REVISION_ID b[7] (MSB) Meaning FEATURE_ID Default 0 0 0 0 0 0 0 0 Read/Write R R R R R R R R FEATURE_ID FEATURE_ID Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 b[3] 0 Register Register Address Name FEATURE 0x05 _ID b[4] Default PRODUCT_ID REVISION 0x04 _ID b[0] (LSB) Meaning MONITOR 0x01 PRODUCT 0x03 _ID b[1] is a registered trademark of Richtek Technology Corporation. DS8088A-00 October 2013 RT8088A Register Name PROG Register Address b[5] b[4] b[3] b[2] b[1] b[0] (LSB) EN Default 1 1 1 0 0 1 0 0 Read/Write R/W R/W R/W R/W R/W R/W R/W R/W VOLT_SEL b[1] b[0] (LSB) 0 : Disabled 1 : Enabled EN VID Table satisfy : SEL [6:0] = 1111111 : VOUT = 1393.75mV ... SEL [6:0] = 1100100 : VOUT = 1.225V (default) ... SEL [6:0] = 0000000 : VOUT = 0.6V 6.25mV step for DCDC, VOUT = 600mV + 6.25mV x SEL VOLT_SEL Register Address b[7] (MSB) Meaning DISCHARGE 0x12 b[6] b[5] RESV b[4] b[3] b[2] DISCHG RESV Default 0 0 0 0 0 0 0 0 Read/Write R R R R/W R R R R b[4] b[3] b[2] b[1] b[0] (LSB) RESV Reserved bits 0 : discharge path disabled 1 : discharge path enabled DISCHG RESV Register Name b[6] Meaning 0x11 Register Name b[7] (MSB) Reserved bits Register Address b[7] (MSB) b[6] b[5] Meaning PWM RESV DVSMODE Default 0 0 0 0 0 0 0 0 Read/Write R/W R R/W R R R R R COMMAND 0x14 PWM 0 : Auto 1 : Forced PWM RESV Reserved bits DVSMODE RESV 0 : Auto DVS transition mode 1 : Forced PWM DVS transition Reserved bits Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8088A-00 October 2013 RESV is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT8088A Register Name Register Address Meaning LIMCONF 0x16 b[6] IPEK <1:0> b[4] b[3] b[2] TPWTH <1:0> b[1] b[0] (LSB) RESV 1 1 1 0 0 0 1 1 Read/Write R/W R/W R/W R/W R R R R TPWTH <1:0> 00 : 2.9A 01 : 2.9A 10 : 3.4A 11 : 3.9A 00 : 83°C 01 : 94°C 10 : 105°C 11 : 116°C Reserved bits Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 14 b[5] Default IPEAK <1:0> RESV b[7] (MSB) is a registered trademark of Richtek Technology Corporation. DS8088A-00 October 2013 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 Maximum Power Dissipation (W)1 RT8088A 4.0 Four-Layer PCB 3.2 2.4 1.6 0.8 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 1. Derating Curve of Maximum Power Dissipation WL-CSP-15B 1.31x2.11 (BSC) package, the thermal resistance, θJA, is 49.8°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 : P D(MAX) = (125°C − 25°C) / (49.8°C/W) = 2W for WL-CSP-15B 1.31x2.11 (BSC) 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 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8088A-00 October 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 15 RT8088A Outline Dimension Symbol Dimensions In Millimeters Dimensions In Inches Min. Max. Min. Max. A 0.500 0.600 0.020 0.024 A1 0.170 0.230 0.007 0.009 b 0.240 0.300 0.009 0.012 D 2.060 2.160 0.081 0.085 D1 E 1.600 1.260 0.063 1.360 0.050 0.054 E1 0.800 0.031 e 0.400 0.016 15B WL-CSP 1.31x2.11 Package (BSC) Richtek Technology Corporation 14F, No. 8, Tai Yuen 1st 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 16 DS8088A-00 October 2013