® RT8472 1A, Hysteretic, High Brightness LED Driver with Internal Switch General Description Features The RT8472 is a high efficiency, continuous mode inductive step-down converter, designed for driving single or multiple series connected LEDs from a voltage source higher than the LED voltage. It operates from an input voltage of 5V to 30V and employs hysteretic control with a high side current sense resistor to set the constant output current. z The RT8472 includes an output switch and a high side output current sensing circuit, which uses an external resistor to set the nominal average output current. LED brightness control is achieved with PWM dimming from an analog or PWM input signal. The RT8472 is available in a small TSOT-23-5 package. z z z z z z z z z z Applications z Ordering Information RT8472 Package Type J5 : TSOT-23-5 Lead Plating System G : Green (Halogen Free and Pb Free) Note : Richtek products are : 5V to 30V Input Voltage Range Hysteretic Control with High Side Current Sensing Internal N-MOSFET with 350mΩ Ω Low RDS(ON) 1A Output Current Up to 97% Efficiency Typical ±5% LED Current Accuracy Analog or PWM Control Signal for LED Dimming 300Hz On-Board Ramp Generator Input Under Voltage Lockout Thermal Shutdown Protection RoHS Compliant and Halogen Free z z z z z Automotive LED Lighting High Power LED Lighting Indicator and Emergency Lighting Architectural Lighting Low Voltage Industrial Lighting Signage and Decorative LED Lighting Pin Configurations ` RoHS compliant and compatible with the current require- (TOP VIEW) ments of IPC/JEDEC J-STD-020. VIN SENSE ` Suitable for use in SnPb or Pb-free soldering processes. 5 4 Marking Information 07= : Product Code 07=DNN DNN : Date Code Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8472-01 March 2013 2 3 LX GND ADJ TSOT-23-5 is a registered trademark of Richtek Technology Corporation. www.richtek.com 1 RT8472 Typical Application Circuit VIN 5V to 30V CIN 10µF/50V RS RT8472 5 VIN SENSE 4 optional 3 ADJ 2 D GND L LX 1 Functional Pin Description Pin No. Pin Name Pin Function 1 LX Switching Node. Open drain output of internal N-MOSFET. 2 GND Ground. 3 ADJ Dimming Control Input : --- Analog signal input for analog PWM dimming. --- PWM signal input for digital PWM dimming. 4 SENSE Output Current Sense Terminal. Sense LED string current. 5 VIN Supply Input Voltage. Function Block Diagram VIN Regulator Bandgap SENSE VCC 1.25V Ramp Gen. UVLO Dimming LX GND + Dimming - Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 2 MOSFET + - ADJ + UVLO - UVLO is a registered trademark of Richtek Technology Corporation. DS8472-01 March 2013 RT8472 Absolute Maximum Ratings (Note 1) Supply Input Voltage, VIN -----------------------------------------------------------------------------------Switch Voltage, LX --------------------------------------------------------------------------------------------z Sense Voltage, SENSE -------------------------------------------------------------------------------------z All Other Pins ----------------------------------------------------------------------------------------------------z Power Dissipation, PD @ TA = 25°C TSOT-23-5 (Single-layer PCB) ------------------------------------------------------------------------------TSOT-23-5 (Four-layer PCB) --------------------------------------------------------------------------------z Package Thermal Resistance (Note 2) TSOT-23-5, θJA (Single-layer PCB) ------------------------------------------------------------------------TSOT-23-5, θJC (Single-layer PCB) ------------------------------------------------------------------------TSOT-23-5, θJA (Four-layer PCB) --------------------------------------------------------------------------z Junction Temperature -----------------------------------------------------------------------------------------z Lead Temperature (Soldering, 10 sec.) -------------------------------------------------------------------z Storage Temperature Range --------------------------------------------------------------------------------z ESD Susceptibility (Note 3) HBM (Human Body Model) ----------------------------------------------------------------------------------MM (Machine Model) -----------------------------------------------------------------------------------------z z Recommended Operating Conditions z z −0.3V to 33V −0.3V to (VIN + 0.7V) (VIN − 5V) to (VIN + 0.3V) −0.3V to 6V 0.400W 0.625W 250°C/W 130°C/W 160°C/W 150°C 260°C −65°C to 150°C 2kV 200V (Note 4) Supply Input Voltage, VIN ------------------------------------------------------------------------------------ 5V to 30V Junction Temperature Range --------------------------------------------------------------------------------- −40°C to 125°C Electrical Characteristics (VIN = 12V, TA = 25°C, unless otherwise specified) Parameter Symbol Test Conditions Measure on SENSE Pin with Respect to VIN. ADJ pin is Floating. Min Typ Max Unit 95 100 105 mV Mean Current Sense Threshold Voltage VSENSE Sense Threshold Hysteresis VSENSEHYS -- ±15 -- % MOSFET On-Resistance MOSFET Leakage Current RDS(ON) VLX = 5V --- 350 0.01 -10 mΩ μA Under Voltage Lockout Threshold VUVLO VIN Rising -- 4 -- V Under Voltage Lockout Threshold Hysteresis Ramp Frequency ΔVUVLO -- 200 -- mV f RAMP -- 300 -- Hz ADJ Input Threshold Voltage Logic-High VADJ_H 1.4 -- 5.5 Logic-Low VADJ_L -- -- 0.2 0.4 -- 1.2 V Analog Dimming Range V Minimum Switch On Time tON(MIN) LX Switch On -- 210 -- ns Minimum Switch Off Time tOFF(MIN) LX Switch Off -- 170 -- ns Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8472-01 March 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 3 RT8472 Parameter Quiescent Supply Current with Output Off Quiescent Supply Current with Output Switching Internal Propagation Delay Symbol tPD Sense Pin Input Current ISENSE Thermal Shutdown Thermal Shutdown Hysteresis TSD ΔTSD Test Conditions Min Typ Max Unit IVIN_Off VADJ = 0V -- 450 -- μA IVIN_On ADJ Pin is Floating, f SW = 250kHz, VIN = 8V -- 1000 -- μA -- 25 -- ns -- 300 -- nA --- 150 30 --- °C °C VSENSE = VIN – 0.1V 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 single-layer and four-layer test board of JEDEC 51. The measurement case position of θJC is on the lead 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 © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 4 is a registered trademark of Richtek Technology Corporation. DS8472-01 March 2013 RT8472 Typical Operating Characteristics Efficiency vs. Input Voltage Output Current Deviation vs. Input Voltage 100 100% 6%6 Output Current Deviation (%) 3 LED 95 95% Efficiency (%) 2 LED 90 90% 85% 85 1 LED 80% 80 75% 75 4%4 3 LED 2%2 2 LED 0%0 1 LED -2% -2 -4% -4 VIN = 5V to 30V, ILED = 1A, L = 33μH VIN = 5V to 30V, ILED = 1A, L = 33μH -6 -6% 70% 70 0 7 14 21 28 35 0 7 Input Voltage (V) 1.03 3%3 1.02 1 LED 2 LED 3 LED 4 LED 5 LED 6 LED 7 LED 8 LED 1 0.99 0.98 0.97 VIN = 5V to 30V, ILED = 1A, L = 33μH 28 35 2%2 1%1 1 LED 2 LED 3 LED 4 LED 5 LED 6 LED 7 LED 8 LED 0%0 -1% -1 -2% -2 -3% -3 VIN = 5V to 30V, ILED = 1A, L = 33μH -4% -4 0.96 0 7 14 21 28 0 35 7 14 21 28 35 Input Voltage (V) Input Voltage (V) Duty Cycle vs. Input Voltage Switching Frequency vs. Input Voltage 850 100% 100 750 90% 90 80% 80 650 Duty cycle (%) Switching Frequency (kHz 21 Output Current Deviation vs. Input Voltage 4%4 Output Current Deviation (%) Output Current (A) Output Current vs. Input Voltage 1.04 1.01 14 Input Voltage (V) 1 LED 2 LED 3 LED 4 LED 5 LED 6 LED 7 LED 8 LED 550 450 350 250 1 LED 2 LED 3 LED 4 LED 5 LED 6 LED 7 LED 8 LED 60% 60 50% 50 40% 40 30% 30 20% 20 150 VIN = 5V to 30V, ILED = 1A, L = 33μH 50 0 70% 70 7 14 21 28 Input Voltage(V) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8472-01 March 2013 35 10 10% VIN = 5V to 30V, ILED = 1A, L = 33μH 0%0 0 7 14 21 28 35 Input Voltage (V) is a registered trademark of Richtek Technology Corporation. www.richtek.com 5 RT8472 Quiescent Input Current vs. Input Voltage Quiescent Input Current vs. Input Voltage 480 Quiescent Input Current (μA) Quiescent Input Current (μA) 1200 1000 800 600 400 200 475 470 465 460 455 450 Output Off VIN = 5V to 30V, ILED = 1A, L = 33μH 445 Output Switching 0 440 0 7 14 21 28 35 0 7 14 Input Voltage (V) 28 35 Output Current vs. PWM Duty Cycle 1200 1200 1000 1000 Output Current (mA) Output Current (mA) Output Current vs. PWM Duty Cycle 800 600 400 200 800 600 400 200 RS = 0.1Ω, fDIMMING = 10kHz 0 0 20 40 60 80 RS = 0.1Ω, fDIMMING = 500Hz 0 100 0 20 40 PWM Duty Cycle (%) 60 80 100 PWM Duty Cycle (%) MOSFET On-Resistance vs. Temperature Output Current vs. ADJ Voltage 600 1200 RS = 100mΩ 550 800 On-Resistance (mΩ) (m ) 1000 Output Current (mA) 21 Input Voltage (V) RS = 150mΩ 600 400 RS = 350mΩ 200 500 450 400 350 300 VIN = 12V, 1LED 0 0.2 0.5 0.8 1.1 1.4 ADJ Voltage (V) Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 6 1.7 250 -50 -25 0 25 50 75 100 125 150 Temperature (°C) is a registered trademark of Richtek Technology Corporation. DS8472-01 March 2013 RT8472 Ramp Frequency vs. Temperature 330 325 325 Ramp Frequency (Hz)1 Ramp Frequency (Hz) Ramp Frequency vs. Input Voltage 330 320 315 310 305 300 320 315 310 305 300 295 295 290 290 0 7 14 21 28 -50 35 -25 0 25 50 75 100 125 Input Voltage (V) Temperature (°C) Digital Dimming from ADJ On Digital Dimming from ADJ Off VADJ (2V/Div) VADJ (2V/Div) IOUT (500mA/Div) IOUT (500mA/Div) VIN = 12V, RS = 0.1Ω, fDIMMING = 500Hz, 1 LED VIN = 12V, RS = 0.1Ω, fDIMMING = 500Hz, 1 LED Time (5μs/Div) Time (5μs/Div) Power On from VIN Power Off from VIN VIN (5V/Div) VIN (5V/Div) IOUT (500mA/Div) IOUT (500mA/Div) RS = 0.1Ω, 1 LED Time (500μs/Div) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8472-01 March 2013 150 RS = 0.1Ω, 1 LED Time (500μs/Div) is a registered trademark of Richtek Technology Corporation. www.richtek.com 7 RT8472 Application Information The RT8472 is a simple high efficiency, continuous mode inductive step-down converter. The device operates with an input voltage range from 5V to 30V and delivers up to 1A of output current. A high side current sense resistor sets the output current and a dedicated PWM dimming input enables pulsed LED dimming over a wide range of brightness levels. A high side current sensing scheme and an onboard current setting circuitry minimize the number of external components. A 1% sense resistor performs a ±3% LED current accuracy for the best performance. Under Voltage Lockout (UVLO) The RT8472 includes a UVLO feature with 200mV hysteresis. The internal MOSFET turns off when VIN falls below 3.8V (typ.). Setting Average Output Current The RT8472 output current which flows through the LEDs is set by an external resistor (RS) connected between the VIN and SENSE terminal. The relationship between output current (IOUT) and RS is shown as below : IOUTavg = 0.1V ( A ) RS Analog Dimming Control The ADJ terminal can be driven by an external voltage (VADJ) to adjust the output current to an average value set by RS. The average output current is given by : ⎛ ⎞ V − 0.4 IOUTavg = ⎜ 0.1V ⎟ × ADJ 0.8 ⎝ RS ⎠ where VADJ is ranged from 0.4V to 1.2V. When VADJ is larger than 1.2V, the output current value will just be set by the external resistor (RS). Digital Dimming Control A Pulse Width Modulated (PWM) signal can drive the ADJ terminal directly. Notice that the PWM signal logic high level must be above 1.4V and the logic low level must be below 0.2V at the ADJ terminal. It's recommended to maintain the PWM dimming at low frequency (ex. 500Hz ) in order to obtain a linear dimming curve. PWM Soft-Start Behavior The RT8472 features an optional PWM soft-start behavior that allows for gradual brightness transition. This is achieved by simply connecting an external capacitor between the ADJ pin and GND. An internal current source will then charge this capacitor for soft-start behavior, resulting in steady LED current increase and decrease during power on and power off, as shown in Figure 1. 1.2V Internal VRAMP 0.4V VADJ 0V 1A ILED 0A Figure 1. PWM Soft-Start Behavior Mechanism Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 8 is a registered trademark of Richtek Technology Corporation. DS8472-01 March 2013 RT8472 The capacitor can be selected according to below equation : -6 where VD is the rectifier diode forward voltage (V) C = 1.5 x 10 x tSS VSEN is the voltage cross current sense resistor (V) where tSS is the soft-start period. RL is the inductor DC resistance (Ω) LED Current Ripple Reduction L is the inductance (H) Higher LED current ripple will shorten the LED life time and increase heat accumulation of LED. By adding an output capacitor in parallel with the LED. This will then allow the use of a smaller inductor. The saturation current of the selected inductor must be higher than the peak output LED current, and the continuous current rating must be above the average output LED current. In general, the inductor saturation current should be 1.5 times the LED current. In order to reduce the output current ripple, a higher inductance is recommended at higher supply voltages. However, it could also cause a higher line resistance and result in a lower efficiency. Inductor Selection The inductance is determined by inductor current ripple, switching frequency, duty ratio, circuit specifications and component parameters, as expressed in the following equation : D L > ⎡ VIN − VOUT − VSEN − RDS(ON) × IOUT ⎤ × ⎣ ⎦ f SW × ΔIL ( ) where fSW is the switching frequency (Hz) RDS(ON) is the on-resistance of internal MOSFET ( = 0.35Ω typical) Diode Selection To obtain better efficiency, the Schottky diode is recommended for its low reverse leakage current, low recovery time and low forward voltage. With its low power dissipation, the Schottky diode outperforms other silicon diodes and increase overall efficiency. D is the duty cycle determined by VOUT/VIN Input Capacitor selection IOUT is the required LED current (A) Input capacitor has to supply peak current to the inductor and flatten the current ripple on the input. The low ESR condition is required to avoid increasing power loss. The ceramic capacitor is recommended due to its excellent high frequency characteristic and low ESR, which are suitable for the RT8472. For maximum stability over the entire operating temperature range, capacitors with better dielectric are suggested. ΔIL is the inductor peak-peak ripple current (internally set to 0.3 x IOUT) VIN is the input supply voltage (V) VOUT is the total LED forward voltage (V) Besides, the selected inductance has also to satisfy the limit of the minimum switch on/off time. The calculated on time must be greater than 210ns of the minimum on time, and the off time must be greater than 170ns of the minimum off time. The following equation can be used to verify the suitability of the inductor value. tON = L × ΔIL VIN − VOUT − IOUT (RSEN + RL + RDS(ON) ) > tON(MIN) (210ns typ.) Thermal Protection A thermal protection feature is included to protect the RT8472 from excessive heat damage. When the junction temperature exceeds a threshold of 150°C, the thermal protection will turn off the LX terminal. When the junction temperature drops below 125°C, the RT8472 will turn back on the LX terminal and return to normal operations. tOFF = L × ΔIL > tOFF(MIN) (170ns typ.) VOUT + VD + VSEN + (IOUT × RL ) Copyright © 2013 Richtek Technology Corporation. All rights reserved. DS8472-01 March 2013 is a registered trademark of Richtek Technology Corporation. www.richtek.com 9 RT8472 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 TSOT-23-5 package, the thermal resistance, θJA, is 250°C/ W on a standard JEDEC 51-3 single-layer thermal test board and 160°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 formulas : 0.8 Maximum Power Dissipation (W)1 Thermal Considerations 0.7 0.6 TSOT23-5 (Four-Layer PCB) 0.5 0.4 0.3 0.2 TSOT23-5 (Single-Layer PCB) 0.1 0.0 0 25 50 75 100 125 Ambient Temperature (°C) Figure 2. Derating Curve of Maximum Power Dissipation Layout Considerations For best performance of the RT8472, please abide the following layout guide. ` The capacitor CIN, CADJ and external resistor, RS, must be placed as close as possible to the VIN and SENSE pins of the device respectively. PD(MAX) = (125°C − 25°C) / (250°C/W) = 0.4W for ` The GND should be connected to a strong ground plane. TSOT-23-5 package (single-layer PCB) ` Keep the main current traces as short and wide as possible. ` The inductor (L) should be mounted as close to the device with low resistance connections. ` The ADJ pin trace need to be kept far away from LX terminal. PD(MAX) = (125°C − 25°C) / (160°C/W) = 0.625W for TSOT-23-5 package (four-layer PCB) The maximum power dissipation depends on the operating ambient temperature for fixed T J(MAX) and thermal resistance, θJA. The derating curves in Figure 2 allow the designer to see the effect of rising ambient temperature on the maximum power dissipation. Place the resistor RS as close as possible to VIN and SENSE pins. RS VIN CIN GND D Place the capacitor CIN as close as possible to VIN pin. LED+ VIN SENSE 5 4 1 2 Place the capacitor CADJ as close as possible to the ADJ pin. 3 LX GND ADJ L CADJ LED- Figure 3. PCB Layout Guide Copyright © 2013 Richtek Technology Corporation. All rights reserved. www.richtek.com 10 is a registered trademark of Richtek Technology Corporation. DS8472-01 March 2013 RT8472 Outline Dimension H D L B C 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-23-5 Surface Mount 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. DS8472-01 March 2013 www.richtek.com 11