BW7381 Universal High Brightness LED Driver FEATURES DESCRIPTION Universal Rectified 90VAC to 264VAC Input The BW7381 is a controller for off-line LED converter. Voltage Range The BW7381 operate with constant off-time, peak Built-in Active Power Factor Correction current mode control with active power factor Technique correction function. The controller senses real-time Low THD, meet with IEC-61000-3-2 Class-C switch current to cycle-by-cycle current limit. High Efficiency Application Cycle-by-cycle current limit at the CS pin ensure a Built-in Output Short Circuit Protection with safe operation during short-circuit at the output. It Auto-Recovery can be configured in either buck-boost (Figure1) Built-in Output Over Voltage Protection with or buck (Figure2) application circuit. The driver Auto-Recovery output voltage is limited to 19V to protect external Built-in Gate Clamp power MOSFET. The controller also monitors Cycle-by-cycle Current Limit integrated actual LED current to perform the Fail-Safe, Output is not subjected to line excellent line and load regulation. The controller voltage if the MOSFET fails. makes the inductor current to follow the shape of Excellently Accurate Constant Current input voltage to perform high power factor and low Very Tight Line and Load Regulation THD solution. Constant Off-Time Buck or Buck-Boost Configuration The BW7381 provides complete protection features such as short-circuit and open-circuit protection. APPLICATIONS AC/DC LED Driver Application DC/DC LED Driver Application Signage and Decorative LED Lighting Residential Lighting ORDER INFORMATION BW 7381- S8 R Bruckewell Circuit Type Shipping: R: Tape & Reel S8: SOP-8 Rev.1.4 Jan. 2013 PIN CONFIGURATIONS (TOP VIEW) BW7381 Universal High Brightness LED Driver PIN DESCRIPTIONS Pin Name Pin Description CS Switch current sense pin. GND IC ground and reference. FLT Actual output current sensing pin. COMP Output pin of error amplifier. RT Constant off-time setting. VIN AC-Line voltage sensing pin. VDD Power supply pin for all internal circuit. OUT Power MOSFET driver output. TYPICAL APPLICATION CIRCUITS Buck-Boost Topology Rev.1.4 Jan. 2013 Figure 1 BW7381 Universal High Brightness LED Driver Buck Topology AC+ V Line L2 C1 AC GND V Line R1 Q1 R10 R5 IC_GND C5 IC_GND R3 C4 IC_GND R2 D1 C6 1 CS OUT 8 2 GND VDD 7 3 CS_FLT VIN 6 4 COMP RT 5 BW7381 C3 R6 IC_GND GND IC_GND IC_GND R12 ZD1 LED+ R9 D2 E1 LED Figure 2 Rev.1.4 Jan. 2013 R7 C2 IC_GND L1 IC_GND R11 BW7381 Universal High Brightness LED Driver ABSOLUTE MAXIMUM RATINGS (Note 1) Parameter Symbol Range Unit Power supply pin VDD -0.3 to 30 V CS voltage to GND VCS -0.3 to 5 V FLT voltage to GND VFLT -0.3 to 5 V VCOMP -0.3 to 5 V VIN voltage to GND VIN -0.3 to 5 V RT voltage to GND VRT -0.3 to 5 V OUT voltage to GND VOUT -0.3 to 30 V Operating junction temperature rang TJ -40 to + 150 °C Operating ambient temperature rang TOPA -40 to +85 °C Storage temperature rang TSTG -65 to +150 °C Lead temperature (Soldering 5 sec) TLEAD 260 °C PD 0.4 W JA 160 °C/W 2 kV COMP voltage to GND Power dissipation @TA=25 °C Thermal resistance junction to ambient (Note 2) ESD rating, Human body mode (Note 3) VESD RECOMMENDED OPERATING CONDITIONS (Note 4) Parameter Symbol Operation Conditions Unit Supply Voltage VDD 20 V Junction Temperature Range TJ -20 to +125 °C Ambient Temperature Range TA -20 to +85 °C Note 1: Stresses listed as the above “Absolute Maximum Ratings” may cause permanent damage to the device. These are for stress ratings. 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 for extended periods may remain possibility to affect device reliability. Note 2: Thermal Resistance is specified with the component mounted on a low effective thermal conductivity test board in free air at TA=25°C. Note 3: Devices are ESD sensitive. Handing precaution recommended. Note 4: The device is not guaranteed to function outside its operating conditions. Rev.1.4 Jan. 2013 BW7381 Universal High Brightness LED Driver BLOCK DIAGRAM Figure 3 Rev.1.4 Jan. 2013 BW7381 Universal High Brightness LED Driver ELECTRICAL CHARACTERISTICS TA= 25°C, unless otherwise specified. Parameter Symbol Condition Min Typ Max Unit VDD(ST) 17 18 19 V VDD(UVLO) 7.5 8.5 9.5 V Over Voltage Protection VOVP 27 28 29 V Start-up Current IINST 42 60 78 uA Operating Current IDDQ 560 800 1040 uA VCSPK 0.67 0.7 0.74 V VDD SECTION Start-up Threshold Under Voltage Lockout Threshold VDD(ST) - 1V CURRENT LIMIT SECTION Maximum Current Sense Voltage Propagation Delay TDLY 70 ns VIREF 0.2 V OUTPUT CURRENT INTEGRATION Reference Voltage ERROR AMPLIFIER SECTION Transconductance GM Maximum Sink Current ISINK 53 uA ISOURCE 58 uA Maximum Source Current 84 120 156 uS LINE SENSING SECTION Source Current ISE(VIN) 375 uA 1.05 V 40.4 us CONSTANT OFF TIME SECTION Regulated Voltage VRT Off-time Setting Range TOFF 0.95 RRT = 136K~17K 1 5.73 TOFF(LV) RT = 50K, 85Vac~150Vac 13.5 15 16.5 us TOFF(HV) RT = 50K, 180Vac~300Vac 18.9 21 23.1 us Rising Time TRISE VDD=12V, C_load=1nF 48 ns Falling Time TFAIL VDD=12V, C_load=1nF 31 ns Clamped Voltage VGATE Constant Off-Time DRIVER SECTION Rev.1.4 Jan. 2013 19 V BW7381 Universal High Brightness LED Driver APPLICATION INFORMATION auto-recovery output while the output open circuit condition removed. In case of output short-circuit 1. Function Description condition. The VDD capacitor cannot get charge The BW7381 is a high performance controller from output voltage. So, the converter repeats which monitors actual output current. These results start-up and UVLO. However, the BW7381provides BW7381 enable tight line and load regulation. The full protections such as OCP, OVP, gate-voltage BW7381 uses constant off-time peak current mode clamp and cycle-by-cycle current limit. control to control the switching current in the MOSFET. At Initial, VDD capacitor charged through start-up resistor until it achieves 18V. Then BW7381 turns-on the MOSFET and make its shape of peak current flow input sine wave. This performs high power factor and low total harmonic distortion. The output current flow through a current sensing resistor and feedback to FLT pin. The controller 2. Pin Detail 2-1. CS MOSFET current sensing, use for cycle by cycle switch peak current control. I L (lim it ) 0.7V R4 always adjusts the amplitude of current command base on the potential of FLT pin. Once the peak current reaches the current command, controller turns off the MOSFET. The resistor connected at RT 2-2. GND GND is the reference node of internal circuit. pin determines the off-time. At the switching on-time, controller senses and limits the maximum switch current by CS pin. This ensures the current in 2-3. FLT MOSFET be limited in safe operating area. Actual output current sensing, the signal The BW7381 built-in output short-circuit and over-voltage protection. While the MOSFET turns feedback to error amplifier and compare with the internal reference voltage (0.2V). off at the off-time, the VDD capacitor can get charge IO by output voltage, and controller can set output over voltage protection threshold by specified zener 0.2V R2 diode. If the LED string is open, the output voltage will be boost over the designed level until the VDD arrive to 28V. The BW7381 goes into over-voltage protection and latches the MOSFET. The controller starts up the system again while the VDD falls to 8.5V (UVLO). Rev.1.4 Jan. 2013 Therefore, the converter 2-4. COMP This is the output of the Gm amplifier. Connect with a suitable RC network to ground. BW7381 Universal High Brightness LED Driver 3. Design Flow 2-5. RT Constant off-time setup. For low-line, 85Vac to 150Vac: toff RT 50 K 15 s toff below please refers to figure 1. 3-1. Input Signal Sampling The BW7381sense input signal from rectified For high-line, 180 to 300Vac: RT 50 K The typical application circuit for design flow line voltage. VIN pin in series with a resistor of 1.6M, R7 to system ground. It is need to pay attention to enough voltage rating for resistor. 21 s 2-6. VIN Sense signal input from the rectified line voltage. R7 1 .6 M 3-2. Low Pass Filter for Switch and Output Current Sensing Two R-C low pass filter are must for MOSFET switch current sensing and actual output current sensing. The following is recommend values : 2-7. VDD Power supply for the controller during normal operation. The controller will start up when VDD reaches 18V (typical) and will shut-down when VDD voltage is below 8.5V (typical). A decoupling capacitor should be connected between the VDD and GND pin as close as possible. R3 4.7 K C4 1 F R5 100 C5 100 pF 3-3. Loop Compensation Place a capacitor of 2.2uF for compensation 2-8. OUT Gate drive for external MOSFET switch. is recommend. C6 2.2 F 3-4. Output Current Sensing Resistor The output current can be set up by a current sensing resistor, R2. The resistance is calculated following the equation below. R2 Rev.1.4 Jan. 2013 0.2V IO BW7381 Universal High Brightness LED Driver 3-5. OVP Threshold Voltage The BW7381 perform output over voltage t (ch arg e) Vac 2 C 2 C3 18 R1 protection though VDD pin. Once VDD pin exceed in 28V, BW7381 turns off and latch out the MOSFET switcher. The OVP threshold voltage can be set by the Zener diode, ZD1. ZD1 The duty cycle in buck-boost converter is a function of Vin and Vo. Duty ( pk ) OVP 28V 3-6. VDD, Supply Current Circuit At the beginning in start-up, the output voltage is not high enough to charge VDD capacitor. Therefore VDD capacitor have to save enough energy for IC operating bias during start-up. To determine the capacitance, we need to calculate the IC operating current, IDD first. IDD 3-8. Off-Time setting the size of an external resistor (RT). The BW7381 automaticall adjusts the off-time with the line voltage (Vac). To calculat the operating off-time and RT, the maximum switching frequency at peak of line cycle must be determined first. C2 toff L R6 IDD 50ms 18V 8.5V C3 100nF Place the VDD capacitor C2 and bypass capacitor C3 as close to IC as possible. Morevoer, a current spike filter resistor R11 is suggest (10 1 Duty ( pk ) toff H to keep enough energy for 50ms. Then the capacitance can be calculated. ~22 freq toff H 1.4 toff H 50 K 21 s where : toffH is the off-time at high-line (180Vac to 300Vac), toffL is the off-time at low-line (90Vac to 135Vac), ) to place between VDD and C3. 3-7. Start-up Resistor At the initial stage, the VDD capacitor get charge through start-up resistor towards the start-up threshold voltage. The smaller start-up resistor the larger power dissipation. The larger start-up resistor the longer charge time. Rev.1.4 Jan. 2013 Vac 2 VO The off-time can be set manually by adjusting Ciss 20 freq 1.5mA In general, assume the VDD capacitor need VO 3-9. Power Inductor Assume a target efficiency to estimate input power and input peak current. Pin VO IO I in( pk ) Pin Vac 2 BW7381 Universal High Brightness LED Driver In buck-boost converter, the average of the CS pin goes execss of 700mV, the BW7381 current flow in MOSFET is equal to the input force MOSFET switcher turn off. Design the peak current. If given a ratio of maximum inductor inductor current to 75 percent of switcher current ripple to maximum inductor peak current, current limit is recommend. L L(pk) Then the inductor peak current can be estimated by the equation: R4 2 I in( pk ) I L ( pk ) IL 2 I L ( pk ) Duty ( pk ) I L (lim it ) The maximum inductor current ripple, L is : IL I L ( pk ) From the IL I L ( pk ) basic inductor equation, the inductance is : L VO IL toff Follow the equations above, the inductance and maximum inductor current can be computed. The magnetic design of the inductor must ensure that there is a sufficient flux density margin to avoid saturation with operating current being applied. 3-10. Switch Current Sensing Resistor The BW7381 sense switch current from CS pin to provide cycle-by-cycle current limit. While Rev.1.4 Jan. 2013 0.53V I L ( peak ) 0.7V R4 BW7381 Universal High Brightness LED Driver PACKAGE OUTLINE DIMENSIONS