RT4501WSC

® RT4501/A High Efficiency Backlight LED Driver General Description Features The RT4501/A is a high-efficiency LED driver for backlight applications. An asynchronous boost converter with an internal Schottky diode and a current source driver are designed to support 6LED/channel with wide input voltage range from 2.5V to 5.5V.  Input Voltage Range : 2.5V to 5.5V  An I2C interface can provide easy backlight control in fast  Internal Schottky Diode Fast-speed mode I2C Compatible Interface Drive Up to 7 WLEDs in 2 String External PWM/Pulse Brightness Control 550k/1.1MHz Switching Frequency Built-in Internal Soft-Start PWM Dimming/Pulse Dimming Resolution 256/128 Steps I 2 C Programmable 256 Steps Linear Current Regulation Up to 85% Efficiency with Small Magnetics Programmable 16V/25.5V OVP Current Accuracy ±5% and Current Balance ±3% UVLO, OVP, OCP, OTP Protection Shutdown Current : < 1μ μA Temperature Range : −40°°C to 85°°C RoHS Compliant and Halogen Free and high speed mode. The RT4501 supports linear mappings with 256 steps to setup the brightness of backlight LEDs. It also supports PWM dimming to adjust the brightness. For brightness dimming, the RT4501A supports 128 steps pulse dimming which determines the LED current, and RT4501 support 256 steps PWM dimming which determines the LED current. The RT4501/A provides complete protection functions such as input under-voltage lockout, over-current, output overvoltage and over-temperature protection. The OVP threshold voltage can be set at 16V and 25.5V for different applications. The RT4501/A is available in the WL-CSP-10B 0.87x2.07 (BSC) package.              Applications     Cellular Phones Digital Cameras PDAs and Smart Phones Portable Instruments Simplified Application Circuit RT4501/A L LX VOUT COUT VIN VOUT VIN CIN Enable EN PWM SCL SDA GND Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS4501/A-00 September 2014 FB1 FB2 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT4501/A Pin Configurations Ordering Information (TOP VIEW) RT4501/A Package Type WSC : WL-CSP-10B 0.87x2.07 (BSC) RT4501 : PWM Dimming RT4501A : Pulse Dimming 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. LX A1 A2 GND VOUT B1 B2 VIN PWM C1 C2 EN SDA D1 D2 SCL FB2 E1 E2 FB1 WL-CSP-10B 0.87x2.07(BSC) Marking Information RT4501WSC RT4501AWSC 1T : Product Code 28 : Product Code W : Date Code 1TW 28W W : Date Code Functional Pin Description Pin No. Pin Name Pin Function A1 LX Switch Node of Boost Converter. Connect an inductor between LX and VIN. A2 GND Ground. B1 VOUT Power Output of the Asynchronous Boost Converter for Backlight LEDs. Connect a 1F or larger ceramic capacitor from VOUT to ground. B2 VIN Power Input. Connect this pin to the input power supply voltage. Connect a 10F or larger ceramic capacitor from the VIN to ground. C1 PWM C2 EN D1 SDA I2C Serial Data Input/Output. An external pull-up resistor is required. D2 SCL I2C Serial Clock Input. An external pull-up resistor is required. E1 FB2 Single Output 2 for Backlight LED. E2 FB1 Single Output 1 for Backlight LED. PWM Dimming Input for Backlight LED. Enable Control Input (Active High). The chip is in shutdown mode when the EN pin is low. Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS4501/A-00 September 2014 RT4501/A Function Block Diagram VIN FB1 Current Source Gen. PWM2DC PWM VREF Digital Control SDA EN LEDs OTP VFB EA SCL LX FB2 OVP VOUT + - PWM Logic VSLOPE OCP GND Operation Description The RT4501/A is a high efficiency solution with 14 WLEDs in 2 parallels 7 series for backlight applications. The RT4501/A optimizes the feedback regulation voltage to provide up to 85% high efficiency with as high as 8bits resolution application. OCP Protection Linear Brightness Dimming OTP Protection 2 The RT4501/A features a 1A current limitation. Once detecting current level over current limitation, the RT4501/A's LX witching will be forced off to avoid large current damage. The RT4501/A is built-in a I C 8-bit resolution brightness control with maximum 20mA/30mA selection. Reg0x02 corresponds to full-scale LED current control. Reg0x04 sets 8bits resolution brightness dimming. The over-temperature protection function will be latched at shutdown status when the junction temperature exceeds 150°C for 2ms. After re-power on sequence, the converter will automatically resume switching. PWM Brightness Dimming OVP Protection 2 Besides programmable built-in I C backlight LED current control, the RT4501 features a built-in PWM dimming current control by setting Reg0x02 to 1, offering a linear current dimming by external clock source. In order to guarantee the PWM dimming resolution, recommending dimming frequency have to be operated at range of 400Hz to 20kHz. The over-voltage protection function monitors the output voltage via the VOUT pin voltage. The OVP threshold voltage is 25.5V/16V by selection Reg0x02, Once the LED is open, the output voltage will be limited at OVP protection level to avoid device breakdown. RT4501 is shunt-down latched, by triggering OVP event over 40 times. Pulse Brightness Dimming The EN pin features a simple digital interface to allow digital brightness control. Using the one-wire dimming brightness control can achieve as high as 128 steps resolution, recommending dimming pulse is larger than 0.2μs. RT4501/A keeps shunt down status, when EN pin is pulled low keeping 1ms. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS4501/A-00 September 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT4501/A Absolute Maximum Ratings            (Note 1) Supply Input Voltage, VIN ----------------------------------------------------------------------------------------------Boost Output Voltage, VOUT ------------------------------------------------------------------------------------------Switching Voltage, LX ---------------------------------------------------------------------------------------------------Current Source Voltage, FB1, FB2 -----------------------------------------------------------------------------------Other Pins, EN, PWM, SCL, SDA -----------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C −0.3V to 6V −0.3V to 27V −0.3V to 27V −0.3V to 27V −0.3V to 6V WL-CSP-10B 0.87X2.07 (BSC) ---------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) WL-CSP-10B 0.87x2.07 (BSC), θJA ---------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------------- 1W Recommended Operating Conditions    99.6°C/W 260°C 150°C −65°C to 150°C 2kV 200V (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 = 3.6V, CIN = 10μF, COUT = 1μF, L = 10μH, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit 2.5 -- 5.5 V Input Power Supply Input Supply Voltage VIN VIN Quiescent Current IQ PWM, No Switching -- 0.6 -- mA Shutdown Current ISHDN VIN = 4.2V, EN = GND -- 1 3 A Under-Voltage Lockout Threshold VUVLO VIN Falling, Check IQ < 200A -- -- 2.3 V Under-Voltage Lockout Hysteresis VUVLO After UVLO, VIN Rising, Until IQ > 200µA -- 200 -- mV Backlight LED Current Source Accuracy of Output Current ILED_ACC FB1, FB2 = 0.15V, IFB1 = IFB2 = 20mA 5 -- 5 % Matching of Output Current ILED_MAT FB1, FB2 = 0.15V, IFB1 = IFB2 = 20mA 3 -- 3 % Operating Frequency f SW Reg0x03 [6] = 1 0.88 1.1 1.32 MHz Maximum Duty Cycle DMAX FB1 = FB2 = 0V, check MAX duty 90 95 -- % Brightness Ramp Rate TRAMP Reg0x03 [5:0] = 111111 Oscillator and Timing Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 209.72 262.14 314.58 ms is a registered trademark of Richtek Technology Corporation. DS4501/A-00 September 2014 RT4501/A Parameter Symbol Test Conditions Min Typ Max Unit Power Switch N-MOSFET On-Resistance RDS(ON)_N VIN = 3.6V 90 175 350 m N-MOSFET Current Limit IOCP 0.8 1 1.2 A N-MOSFET Leakage Current ILEAK LX = 24V, No Switching -- -- 1 A Reg0x02 [7] = 0 14 16 18 V Reg0x02 [7] = 1 24.5 25.5 26.5 V -- 150 -- °C Protection Function Over Voltage Protection Thermal Shutdown Threshold OVP TSD Thermal latch Logic Control Logic-High VENH 1.3 -- -- Logic-Low VENL -- -- 0.4 Logic-High VPWML 1.3 -- -- Logic-Low VPWML -- -- 0.4 Logic-High VSCLH 1.3 -- -- Logic-Low VSCLL -- -- 0.4 Logic-High VSDAH 1.3 -- -- Logic-Low VSDAL -- -- 0.4 EN Pull-Down Resistance -- 400 -- k PWM Pull-Down Resistance -- 400 -- k f SCL -- -- 400 kHz tOFF 1 -- -- ms tHigh_Min 0.2 -- -- s tLow 0.2 -- 500 s EN Input Voltage PWM Input Voltage SCL Input Voltage SDA Input Voltage Clock Frequency of SCL Pulse Dimming Control EN Minimum Shut Down Pulse Width EN Minimum Logic High Pulse Width EN Minimum Logic Low Pulse Width V V V 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. Note 3. Devices are ESD sensitive. Handling precaution is recommended. Note 4. The device is not guaranteed to function outside its operating conditions. Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS4501/A-00 September 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT4501/A Typical Application Circuit L 10µH VIN 2.5V to 5.5V RT4501/A 10 2 CIN 10µF 3 Enable LX VOUT 9 COUT 1µF VIN VOUT EN 1 PWM 4 SCL 5 SDA 8, 11 (Exposed Pad) GND FB1 7 FB2 6 Timing Diagram PWM Dimming Reg0x04 = FF Reg0x04 = Reg0x02 = C7 Count 2^17 Clock As Reg Default 00 PWM Enable EN Count 2^17 Clock Reg0x02 = 0 DEV_EN Disable Duty =50% PWM I(MAX) I(MAX)/2 I(LED) I(MIN) 0 0 Note : PWM prd : count by OSC : 17.6MegHz > 1024 : Resolution = 7bits & < 1000 : Resolution = 8bits Pulse Dimming 32µs/step x 127 steps POR = 1 & EN power on Hold at least 50µs EN 32µs/step x 127 steps Ton > 0.2µs 0.2µs < Toff < 500µs 1ms 7bits = 1111111 = I(LED)max *[127/128+1/256] MAX 7bits = 1111010 I(LED) MIN OFF 32µs/step 32µs/step 7bits = 0000000 = I(LED)max*1/256 7bits = 1111111 7bits = 1111100 Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS4501/A-00 September 2014 RT4501/A Protection Timing OTP EN 2ms sOTP 2ms sEnbl Reg0x05 record Register LED Short EN FB1 or FB2 Short 2ms 2ms sEnbl Reg0x05 record Register LED Open EN 40 times sOVP … x 39 times sEnbl Register Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS4501/A-00 September 2014 Reg0x05 record is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT4501/A Typical Operating Characteristics Power On Power Off VEN (2V/Div) VEN (2V/Div) VOUT (10V/Div) VOUT (10V/Div) ILX (200mA/Div) ILX (200mA/Div) CIN = 10μF, COUT = 1μF, L = 10μH CIN = 10μF, COUT = 1μF, L = 10μH Time (5ms/Div) Time (10ms/Div) Efficiency vs. Output Current Efficiency vs. Input Voltage 100 100 95 95 90 VIN = 3.7V VIN = 4.2V 85 80 Efficiency (%) Efficiency (%) 90 75 70 65 60 ILED = 20mA ILED = 30mA 85 80 75 70 65 60 55 55 CIN = 10μF, COUT = 1μF, L = 10μH 50 CIN = 10μF, COUT = 1μF, L = 10μH 50 0 5 10 15 20 25 30 2.5 3 Output Current (mA) 4 4.5 5 5.5 Input Voltage (V) OVP Threshold vs. Input Voltage LED Current Accuracy vs. Input Voltage 26 2.00 1.80 Reg0x02 [7] = 1, 23V 24 1.60 ILED _30mA ILED_20mA 1.40 OVP Threshold (V) LED Current Accuracy (%) 3.5 1.20 1.00 0.80 0.60 0.40 22 20 18 Reg0x02 [7] = 0, 16V 16 0.20 6S2PWLED 0.00 2.5 3 3.5 4 4.5 5 Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 5.5 14 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. DS4501/A-00 September 2014 RT4501/A PWM Dimming Operation PWM Dimming 35 LED Current (mA) 30 ILED2 = 20mA ILED1 = 20mA 25 20 VPWM (2V/Div) 15 ILED2 = 20mA ILED1 = 20mA 10 I LED (10mA/Div) 5 Frequency = 20kHz, Duty Cycle = 50% 0 0 10 20 30 40 50 60 70 80 90 100 Time (10μs/Div) Dimming Duty (%) Quiescent Current vs. Input Voltage 800 1.11 700 Quiescent Current (μA) 1 Switching Frequency (MHz)1 Switching Frequency vs. Input Voltage 1.12 1.10 1.09 1.08 1.07 1.06 Non-Switching 600 500 400 300 200 100 CIN = 10μF, COUT = 1μF, L = 10μH 1.05 2.5 3 3.5 4 4.5 5 0 5.5 2.5 3 Input Voltage (V) 3.5 4 4.5 5 5.5 Input Voltage (V) Shutdown Current vs. Input Voltage Enable Voltage vs. Input Voltage 0.35 0.94 Enable Voltage (V) Shutdown Current (μA)1 0.30 0.25 0.20 0.15 0.10 0.93 Enable Shutdown 0.92 0.05 0.00 0.91 2.5 3 3.5 4 4.5 5 Input Voltage (V) Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS4501/A-00 September 2014 5.5 2.5 3 3.5 4 4.5 5 5.5 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT4501/A Table 1. Pulse Dimming Register Map Slave address =0100010x Address Address Name 0x00 Device ID 0x01 0x02 0x03 0x05 Manufacture Config1 Timing FLAG BIT LABEL Description 7:0 DEV_ID 7:2 REV 000000 Revision number 1:0 VID 11 Vendor ID : Richtek 7 OVPsel 1 OVP threshold ([0] 16V, [1] 25.5V) 6 Reserved 5 Reserved 4 Reserved 3 MAX_Current 0 [0] 20mA, [1] 30mA, 2 LED1_EN 1 Backlight LED1 : [0] OFF, [1] ON 1 LED2_EN 1 Backlight LED2 : [0] OFF, [1] ON 0 DEV_EN 1 CHIP enable : [0] OFF, [1] ON 7 RST_SW 0 Software reset : [0] Disable(Auto), [1] Reset all registers 6 FSW 1 Switching frequency ([0]550kHz, [1]1.1MHz) 5:0 Reserved 7:4 Reserved 0 3 LED1_FT 0 LED1 short : [0] Normal, [1] Fault 2 LED2_FT 0 LED2 short : [0] Normal, [1] Fault 1 OVP 0 Output over voltage : [0] Normal, [1] Fault 0 OTP 0 Over temperature : [0] Normal, [1] Fault Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 Default (Reset Value) is a registered trademark of Richtek Technology Corporation. DS4501/A-00 September 2014 RT4501/A Table 2. PWM Dimming Register Map Slave address =0100010x Address Address Name 0x00 Device ID 0x01 0x02 Manufacture Config1 BIT 0x04 0x05 7:2 REV 000000 Revision number 1:0 VID 11 Vendor ID : Richtek 7 OVPsel 1 OVP threshold ([0] 16V, [1] 25.5V) 6 PWM_EN 0 PWM enable : [0] Ignored, [1] Enable 0 PWM active setup : [0] High active, [1] Low active 5 PWM _SET 4 Reserved 3 MAX_Current 0 [0] 20mA, [1] 30mA, 2 LED1_EN 1 Backlight LED1 : [0] OFF, [1] ON 1 LED2_EN 1 Backlight LED2 : [0] OFF, [1] ON 0 DEV_EN 1 CHIP enable : [0] OFF, [1] ON 7 RST_SW 0 Software reset : [0] Disable(Auto), [1] Reset all registers 6 FSW 1 Switching frequency ([0]550kHz, [1]1.1MHz) 000 Brightness ramp-up rate : [000] 32s, [001] 4.096ms, [010] 8.192ms, [011] 16.383ms, [100] 32.768ms, [101] 65.536ms, [110] 131.072ms, [111] 262.144ms UP_RATE Timing Linear Brightness Control FLAG Description DEV_ID 2:0 DN_RATE 000 Brightness ramp-down rate : [000] 32µs, [001] 4.096ms, [010] 8.192ms, [011] 16.383ms, [100] 32.768ms, [101] 65.536ms, [110] 131.072ms, [111] 262.144ms 7:0 BRIGHT_LIN 11111111 [00000000] 0.39%, [00000001] 0.39%, …… [111111111] 100% 7:4 Reserved 0 3 LED1_FT 0 LED1 short : [0] Normal, [1] Fault 2 LED2_FT 0 LED2 short : [0] Normal, [1] Fault 1 OVP 0 Output over voltage : [0] Normal, [1] Fault 0 OTP 0 Over temperature : [0] Normal, [1] Fault Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS4501/A-00 Default (Reset Value) 7:0 5:3 0x03 LABEL September 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 11 RT4501/A Application Information LED Short Protection LED short protection prevents abnormal connection to cause IC damage avoiding FB1/FB2 connecting power supply. And, If unbalanced LEDs series (cause FB1 or FB2 >12V) is different between channel1 and channel2, IC will also occur LED short event. As LED short event occur more than deglitch time 2ms, IC will shut-down latch until IC is reset by EN pin. Soft-Start The RT4501/A includes a soft-start function to avoid high inrush current during start-up. The soft-start function is achieved by clamping the output voltage of the error amplifier with another voltage source that is increased slowly from zero to near VIN during the soft-start period. threshold, the device is shut down. If the input voltage rises over under-voltage lockout hysteresis (200mV typical), the IC restarts. Linear Brightness Dimming The chip is built-in an I2C 8-bit resolution brightness control with maximum 20mA/30mA selection. Reg0x02 corresponds to full-scale LED current control. Reg0x04 sets 8bits resolution brightness dimming control. ILED = Code  ILED, Full 255 Where ILED, Full : the full-scale LED current set by Reg0x02 . Code : the 8bit brightness code Reg0x04 programmed by I2C interface. OCP Protection The RT4501/A features a 1A current limitation. The current flowing through the inductor during a charging period is detected by a current sensing circuit. If the value exceeds the current limit, the N-MOSFET will be turned off. The inductor will then be forced to leave charging stage and enter discharging stage. Therefore, the inductor current will not increase to reach current limit. The over-temperature protection function will be latched at shutdown status when the junction temperature exceeds 165°C for 2ms. After re-power on sequence, the converter will automatically resume switching. OVP Protection The chip provides over-voltage protection function to limit the output voltage in abnormal conditions. The OVP threshold voltage is 25.5V/16V by selecting Reg0x02 . Once the LED is open, the output voltage will be limited at OVP protection level to avoid device breakdown. PWM Brightness Dimming Besides programmable built-in I2C backlight LED current control, the RT4501/A features a built-in PWM dimming current control by setting Reg0x02 to 1, offering a linear current dimming by external clock source. In order to guarantee the PWM dimming resolution (7 bit at > 15kHz application), recommending dimming frequency have to be operated at range of 400Hz to 20kHz. Pulse Brightness Dimming The EN pin features a simple digital interface to allow digital brightness control. Using the one-wire dimming brightness control can achieve as high as 128 steps resolution, recommending dimming pulse is larger than 0.2μs. RT4501/A keeps shunt down status, when EN pin is pulled low keeping 1ms. 1   Code ILED =  +   ILED, Full 256   128 Where Under-Voltage Lockout ILED, Full : the full-scale LED current set by Reg0x02 . An under-voltage lockout circuit prevents the operation of the device at input voltages below under-voltage threshold (2.3V maximum). When the input voltage is below the Copyright © 2014 Richtek Technology Corporation. All rights reserved. www.richtek.com 12 is a registered trademark of Richtek Technology Corporation. DS4501/A-00 September 2014 RT4501/A The recommended inductor value for dual-channel 6 WLEDs applications is 10μH. When selecting the inductor, the inductor rated saturation current should be higher than the peak current at maximum load. Small size and better efficiency are major concerns for portable devices. The inductor should have low core loss at 1.1MHz and low DCR for better efficiency. Capacitor Selection 10μF input ceramic capacitor and 1μF output ceramic capacitor are recommended for driving dual-channel 6 WLEDs applications. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wide voltage and temperature ranges. 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 WL-CSP-10B 0.87x2.07 (BSC) package, the thermal resistance, θJA, is 99.6°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 : resistance, θJA. The derating curve in Figure 1 allows the designer to see the effect of rising ambient temperature on the maximum power dissipation. 1.2 Maximum Power Dissipation (W)1 Inductor Selection Four-Layer PCB 1.0 0.8 0.6 0.4 0.2 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 1. Derating Curve of Maximum Power Dissipation Layout Consideration As for all switching power supplies, the layout is an important step in the design, especially at high peak currents and switching frequencies. If the layout is not carefully done, the regulator might expose noise problems and duty cycle jitter. Therefore, use wide and short traces for high current paths. The input capacitor should be placed as close as possible to the input pin for good input voltage filtering. The inductor should be placed as close as possible to the switch pin to minimize the noise coupling into other circuits. The output capacitor needs to be placed directly from the VOUT pin to GND rather than across the LEDs. This reduces the ripple current in the trace to the LEDs. When doing the PCB layout, the bold traces should be routed first, as well as placement of the inductor, and input and output capacitors. P D(MAX) = (125°C − 25°C) / (99.6°C/W) = 1W for WL-CSP-10B 0.87x2.07 (BSC) package The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal Copyright © 2014 Richtek Technology Corporation. All rights reserved. DS4501/A-00 September 2014 is a registered trademark of Richtek Technology Corporation. www.richtek.com 13 RT4501/A 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 2.020 2.120 0.080 0.083 D1 E 1.600 0.820 0.063 0.920 0.032 0.036 E1 0.400 0.016 e 0.400 0.016 10B WL-CSP 0.87x2.07 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 14 DS4501/A-00 September 2014