® RT4533/A Asynchronous Boost Converter for 10 WLEDs General Description Features The RT4533/A is a highly integrated LED driver IC capable of driving 10 WLEDs in series. It is composed of a current mode Boost converter integrated with a 36.5V/1.2A power switch. 2.5V to 5.5V Input Voltage Range 36.5V Open LED Protection for 10 WLEDs PWM Dimming Brightness Control 200mV / 300mV Reference Voltage with ± 2% Accuracy 1.1MHz Switching Frequency Built-In Soft-Start Over-Temperature Protection Internal Compensation Current Limit RoHS Compliant and Halogen Free The RT4533/A supports a wide input voltage range from 2.5V to 5.5V and runs at a fixed frequency of 1.1MHz. The LED current is set via an external resistor and the feedback voltage is regulated to 200mV / 300mV. For brightness dimming, the RT4533/A supports PWM dimming which determines the feedback reference voltage. Applications Ordering Information Cellular Phones Digital Cameras Probable Instruments RT4533/A Package Type J6 : TSOT-23-6 Lead Plating System G : Green (Halogen Free and Pb Free) Marking Information Feedback Voltage RT4533 : 200mV RT4533A : 300mV RT4533GJ6 0R= : Product Code 0R=DNN DNN : Date Code Note : Richtek products are : RT4533AGJ6 1L= : Product Code 1L=DNN DNN : Date Code Simplified Application Circuit RoHS compliant and compatible with the current requirements of IPC/JEDEC J-STD-020. Suitable for use in SnPb or Pb-free soldering processes. D L VOUT LX VIN VIN VOUT RT4533/A … Enable EN GND FB Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4533/A-02 September 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT4533/A Pin Configurations (TOP VIEW) VIN VOUT EN 6 5 4 2 3 LX GND FB TSOT-23-6 Functional Pin Description Pin No. Pin Name Pin Function 1 LX Switch Node. 2 GND Ground. 3 FB Feedback Voltage Input. Put a resistor to GND to setting the current. 4 EN Enable Control Input (PWM Dimming). 5 VOUT Output Voltage Pin. 6 VIN Supply Voltage Input. Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 is a registered trademark of Richtek Technology Corporation. DS4533/A-02 September 2015 RT4533/A Function Block Diagram LX VIN UVLO VOUT OCP Internal Compensation Internal Soft-Start OVP OTP Logic Control, Minimum On Time PWM CurrentSense + + EA GM Driver GND + - Slope Compensation LPF Enable Logic Shutdown 20ms PWM Oscillator Reference Voltage VREF Bias Current FB EN Operation The RT4533/A is a constant frequency, current mode Boost LED driver. In normal operation, the N-MOSFET is turned on when the PWM Control circuit is set by the oscillator and is turned off when the current comparator resets the PWM Control circuit. While the N-MOSFET is turned off, the inductor current conducts through the external diode. OCP The driver provides cycle-by-cycle current limit function to control the current on power switch. The boost switch turns off when the inductor current reaches this current threshold and it remains off until the beginning of the next switching cycle. This protects the RT4533/A and external component under overload conditions. UVLO OVP When the input voltage is lower than the UVLO threshold (2.37V typ.), the driver will turn off. There is a 80mV for the UVLO hysteresis control. The Over Voltage Protection is detected by a resistor divider circuit from VOUT. Soft-Start When the device is enabled, the Comp ramps up to the target voltage in a specific time. This ensures that the output voltage rises slowly to reduce the input inrush current. EN Dimming The EN pin is used for the control input for both PWM dimming mode and digital dimming mode. Shutdown delay when the EN voltage is logic low for more than specific time, the driver will be shut down. Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4533/A-02 September 2015 Once VOUT goes over the OVP voltage, LX pin stops switching and the power N-MOSFET will be turned off. Then, the VOUT will be discharged by external resistor. OVP will be released until EN goes from Lo to Hi again. OTP As the die temperature is higher than 160°C, the chip also will enter protection mode. The power MOSFET will be turned off during protection mode to prevent abnormal operation. The device is released from shutdown automatically when the junction temperature decreases by 15°C. is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT4533/A Absolute Maximum Ratings (Note 1) VIN ---------------------------------------------------------------------------------------------------------------------EN, FB to GND ------------------------------------------------------------------------------------------------------LX to GND ------------------------------------------------------------------------------------------------------------VOUT to GND ---------------------------------------------------------------------------------------------------------Power Dissipation, PD @ TA = 25°C TSOT-23-6 ------------------------------------------------------------------------------------------------------------Package Thermal Resistance (Note 2) TSOT-23-6, θJA ------------------------------------------------------------------------------------------------------Junction Temperature ----------------------------------------------------------------------------------------------Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------Storage Temperature Range -------------------------------------------------------------------------------------ESD Susceptibility (Note 3) HBM (Human Body Model) ---------------------------------------------------------------------------------------MM (Machine Model) ----------------------------------------------------------------------------------------------- Recommended Operating Conditions −0.3V to 6V −0.3V to (VIN + 0.3V) −0.3V to 38V −0.3V to 40V 0.5W 197.4°C/W 150°C 260°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 = 4.7μF, COUT = 1μF, L = 22μH, fSW = 1.1MHz, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Min Typ Max Unit VFB = 0V 0.25 0.8 1.5 mA IC Quiescent Current (non-switching) IQ VFB = 0.4V 0.25 0.35 0.5 mA VIN Pin Shutdown Current ISD EN = GND -- 0.3 1 A Under-Voltage Lockout Threshold, UVLO VIN Rising Edge 2.25 2.37 2.5 V Under-Voltage Lockout Hysteresis UVLO_hys VIN Falling Edge -- 80 -- mV Power Supply IC Operating Current (switching) IQ_SW Enable and Reference Control Logic-High VIH 1.4 -- -- Logic-Low VIL -- -- 0.4 EN Pull Low Resistance REN -- 300 -- k EN Minimum Shut down Pulse Width Toff 20 -- -- ms EN Minimum Logic High Pulse Width THigh_Min 0.5 -- -- s EN Minimum logic low pulse width TLow 1 -- 10000 s Internal Comp Resistance Rcomp -- 7 -- M PWM Minimum Duty Dpwm min -- 3 -- % PWM Frequency f PWM 5 -- 100 kHz EN Input Voltage Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 V is a registered trademark of Richtek Technology Corporation. DS4533/A-02 September 2015 RT4533/A Parameter Symbol Test Conditions Min Typ Max 196 200 204 294 300 306 Unit Voltage And Current Control Feedback Regulation Voltage RT4533 RT4533A VFB mV Feedback Pin Bias Current IFB -- -- 0.1 A Oscillator Frequency f SW 0.99 1.1 1.21 MHz Maximum Duty Cycle DMAX -- 93 -- % -- 0.4 0.7 Power Switch N-MOSFET On-Resistance RDS(ON) VIN = 3.6V OC and OLP Peak N-MOSFET Current Limit ILIM 1.0 1.2 1.4 A Open LED Protection Threshold OVP 35 36.5 38 V Thermal Shutdown Threshold TSD -- 160 -- °C Thermal Shutdown Hysteresis TSD -- 15 -- °C Thermal Shutdown 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 © 2015 Richtek Technology Corporation. All rights reserved. DS4533/A-02 September 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT4533/A Typical Application Circuit L 10µH to 22µH D VOUT 1 LX VIN 6 CIN 4.7µF VOUT 5 COUT 1µF / 50V RT4533/A 2 … 4 Enable VIN EN 10 WLEDs GND FB 3 RSET Timing Diagram Period1 EN Period2 5kHz < FPWM < 100kHz TSHDN > 20ms on-time1 on-time2 Duty1 x 200mV Duty1 x 300mV Duty2 x 200mV Duty2 x 300mV FB Duty1 : on-time1/Period1 Duty2 : on-time2/Period2 Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 is a registered trademark of Richtek Technology Corporation. DS4533/A-02 September 2015 RT4533/A Typical Operating Characteristics Efficiency vs. Input Voltage Efficiency vs. Output Current 100 100 90 90 80 5.5V 4.2V 3.7V 70 60 Efficiency (%) Efficiency (%) 80 50 40 30 Load = 30mA Load = 20mA 70 60 50 40 30 20 20 10 10 VOUT = 30V 0 VOUT = 30V 0 0 0.005 0.01 0.015 0.02 0.025 0.03 2.5 3 3.5 Output Current (A) 4.5 5 5.5 Input Voltage (V) ILED vs. Duty Operating Quiescent Current vs. Input Voltage 1.20 35 1.10 30 25 1.00 I LED (mA) Quiescent Current (mA) 4 0.90 20 15 0.80 10 0.70 5 Switching Quiescent Current RT4533A PWM Frequency = 10kHz 0.60 0 2.5 2.8 3.1 3.4 3.7 4 4.3 4.6 4.9 5.2 5.5 0 10 20 30 Input Voltage (V) 40 50 60 70 80 90 100 Duty (%) Oscillator Frequency vs. Temperature Reference Voltage vs. Output Current 200.5 1.25 Reference Voltage (mV) Oscillator Frequency (MHz)1 3.7V 1.20 1.15 1.10 1.05 200.4 200.3 200.2 4.2V 200.1 200 199.9 RT4533 1.00 199.8 -50 -25 0 25 50 75 100 Temperature (°C) Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4533/A-02 September 2015 125 0 3 6 9 12 15 18 21 24 27 30 Output Current (mA) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT4533/A Application Information Soft-Start The RT4533/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. analog dimming. This eliminates the audible noise which often occurs when the LED current is pulsed in replica of the frequency and duty cycle of PWM control. For optimum performance, use the PWM dimming frequency in the range of 5kHz to 100kHz, and the PWM dimming frequency is strongly suggested to be over than 20kHz to avoid audio noise. LED Current The loop control of the Boost converter keeps VFB equal to a reference voltage, VREF. Therefore, when RSET is connected between the FB pin and GND, the LED current will be determined by the current through RSET, which is equal to VFB / RSET. Current Limit 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. Inductor Selection The recommended value of inductor for 10 LEDs or high brightness LED applications is 10μH to 22μH. Smaller size and better efficiency are the major concerns for portable devices. The inductor should have low core loss at 1MHz and low DCR for better efficiency. The inductor saturation current rating should be considered to cover the inductor peak current. Table 1 lists the recommended inductor for the RT4533/A. Table 1 Part Number DCR Saturation Size (L x L Vendor MAX (H) Current (A) W x H mm) (m) NR4018T100M 10 216 1.2 4 x 4 x 1.8 TAIYO NR4018T220M 22 432 0.8 4 x 4 x 1.8 TAIYO Shutdown Delay When the EN voltage is in logic low for 20ms during PWM dimming, the system will enter shutdown. Capacitor Selection PWM Dimming When the EN pin is constantly high, the FB voltage is regulated to 200mV / 300mV typically. The RT4533/A allows a PWM signal from EN pin to reduce the regulation voltage; and achieve LED brightness dimming. The relationship between the duty cycle and FB voltage is given by VFB = Duty VREF Where Duty = duty cycle of the PWM signal VREF = internal reference voltage (200mV / 300mV typ.) The RT4533/A choose the internal 200mV reference voltage via the duty cycle of the PWM signal. Therefore, although a PWM signal is used for brightness dimming, only the LED DC current is modulated, which is often referred as Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 For low ripple voltage, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wide voltage range and good operating temperature characteristics. For the application of the RT4533/A to drive 10 LEDs in series, a 4.7μF for input capacitor, an 1μF / 50V for output capacitor. Thermal Considerations For continuous operation, do not exceed absolute maximum operation junction temperature. 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 : PD(MAX) = ( TJ(MAX) − TA ) / θJA is a registered trademark of Richtek Technology Corporation. DS4533/A-02 September 2015 RT4533/A 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. Layout Consideration For recommended operating condition specifications, the maximum junction temperature is 125°C. The junction to ambient thermal resistance, θJA, is layout dependent. For TSOT-23-6 package, the thermal resistance, θJA, is 197.4°C/W on the standard JEDEC 51-7 four-layer thermal test board. The maximum power dissipation at TA = 25°C can be calculated by following formula : Input and Output capacitors should be placed close to the IC and connected to ground plane to reduce noise coupling. The GND and Exposed Pad should be connected to a strong ground plane for heat sinking and noise protection. Keep the main current traces as possible as short and wide. LX node of DC/DC converter is with high frequency voltage swing. It should be kept at a small area. Place the feedback components as close as possible to the IC and keep away from the noisy devices. PD(MAX) = (125°C − 25°C) / (197.4°C/W) = 0.5W for TSOT-23-6 package The maximum power dissipation depends on operating ambient temperature for fixed T J(MAX) and thermal resistance θJA. The derating curve in Figure 1 of derating curves allows the designer to see the effect of rising ambient temperature on the maximum power allowed. Maximum Power Dissipation (W)1 0.6 For best performance of the RT4533/A, the following guide lines must be strictly followed. Four-Layer PCB 0.5 0.4 0.3 0.2 0.1 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 1. Derating Curve of Maximum Power Dissipation Copyright © 2015 Richtek Technology Corporation. All rights reserved. DS4533/A-02 September 2015 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT4533/A The inductor should be placed as close as possible to the switch pin to minimize the noise coupling into other circuits. LX node copper area should be minimized for reducing EMI. GND The COUT should be connected directly from the output schottky diode to ground rather than across the WLEDs COUT VIN CIN should be placed as closed as possible to VIN pin for good filtering. D L LX 1 6 VIN GND 2 5 VOUT 3 4 EN CIN RSET FB FB node copper area should be minimized and keep far away from noise sources (LX pin) and RS should be as close as possible to FB pin. WLEDs It recommended to add 100 Ohm between IC's VOUT and WLED's anode for improving system ESD level. Figure 2. PCB Layout Guide Copyright © 2015 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS4533/A-02 September 2015 RT4533/A Outline Dimension H D L C B b A A1 e Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.700 1.000 0.028 0.039 A1 0.000 0.100 0.000 0.004 B 1.397 1.803 0.055 0.071 b 0.300 0.559 0.012 0.022 C 2.591 3.000 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 H 0.080 0.254 0.003 0.010 L 0.300 0.610 0.012 0.024 TSOT-23-6 Surface Mount Package 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. DS4533/A-02 September 2015 www.richtek.com 11