BL8549 40V Backlight LED Driver with PWM Direct Dimming DESCRIPTION FEATURES The BL8549 is a high efficiency current-mode asynchronous, 40V boost converter for LED backlight driving. Its input voltage ranges from 2.5V to 4.5V and it provides an adjustable constant current output decided by the Rset connected to BL8549’s FB pin. The LED brightness can also be controlled by a PWM signal directly set to CE pin, making dimming control very simple. Adjustable Output Voltage, Vfb=0.2V Output voltage 40V, driving up to 12 LED string Range of operation input voltage: 2.5 – 4.5V Output Overvoltage Protection @40V CE pin PWM direct dimming function Line regulation: 0.1%/V (typ.) Load regulation: 10mV (typ.) High efficiency, up to 90% in driving 10 LEDs Environment Temperature: -20C~85C APPLICATIONS The BL8549’s switching frequency is set to 600KHz, and it will automatically switch between PFM and PWM mode based on the load current, thus to enhance the converter efficiency at light load as well as heavy load. BL8549 consists of many protection blocks such as UVLO, output voltage over voltage protection, and thermal protection to keep the chip and load safe under unexpected environment. Smartphone 7” MID Portable DVD TFT LCD bias Portable LED lighting or torch Other application need high voltage The BL8549 is available in the tiny DFN2x2-6 and SOT23-6 package. TYPICAL APPLICATION and PIN OUT Efficiency for Driving 10 LEDs Efficiency VS Iout for 10 LEDs 100 95 90 BL8549 85 Efficiency (%) 80 75 70 65 60 Vin=3.6V 55 Vin=3.8V 50 Vin=4.2V 45 40 0 10 20 30 Output Current (mA) www.belling.com.cn 1 40 50 BL8549 PACKAGE, MARK and ORDERING INFORMATION Package DFN2x2-6 Mark Explanation Ordering Information Package SOT23-6 LT: Product ID: Product Code BL8549CKCTR LT YW YW: Date Code SW CE VIN 6 5 4 LTYW XXYW Devices/Reel: 3000 1 2 COMP GND 3 FB Mark Explanation Ordering Information LT: Product Code Product ID: BL8549CB6TR YW: Date Code Devices/Reel: 3000 SOT23-6 PINOUT DESCRIPTION NAME FB Comp GND SW PIN # DFN2x2-6 SOT23-6 1 3 2 1 3 2 4 6 CE 5 5 VIN 6 4 DESCRIPTION Feedback input with reference voltage set to 0.2V Compensation pin, to connect a 220nF capacitor to make loop stable. Ground. Power switching node to connect inductor Chip enable, but a PWM signal with various duty cycle can directly sent to CE pin to achieve the backlight dimming Power input, 1uf input capacitor is recommended. BLOCK DIAGRAM FB SW Vin Comp CE GND www.belling.com.cn 2 BL8549 ABSOLUTE MAXIMUM RATING Parameter Value Max Input Voltage Max Output Voltage (SW pin) Max Operating Junction Temperature(Tj) Ambient Temperature(Ta) DFN2x2-6 (JC) Package Thermal Resistance DFN2x2-6 (JA) Storage Temperature(Ts) Lead Temperature & Time ESD (HBM) 5.5V 40V 125C -20C – 85C 20C / W 140C / W -40C - 150C 260C, 10S >2000V Note: Exceed these limits to damage to the device. Exposure to absolute maximum rating conditions may affect device reliability. RECOMMENDED WORK CONDITIONS Parameter Value Input Voltage Range Operating Junction Temperature(Tj) 2.5V – 4.5V -20C –125C ELECTRICAL CHARACTERISTICS (VIN=12V, TA=25C) Symbol Parameter Conditions Vin Input Voltage Range Vref Feedback Voltage Vin=3.6V, Vce=Vin VUVLO UVLO Voltage Vin H-->L, Iout=0.5A Ifb Iq LnReg Shutdown, Vin=3.6V Vin=2.5V to 4.5V Vin=Vce=3.6V Low side Switch Rdson Isw=200mA Ilimit Peak Inductor Current Limit Vin=3.6V, Vout=32V Vceh CE High Threshold Vcel CE Low Threshold Vovp Output Over-Voltage Protection Vce=3.6V TSD Over Temperature Proection Hystersis=40C Toff CE pin pulse width to shutdown CE high to low Fpwm_CE 4.5 V 0.210 V V 0.1 0.4 uA 0.6 1.0 mA 1 5 uA %/V 600 750 KHz 300 500 mohm 0.8 1 1.4 A 1 1.5 3 V 0.3 V 40 42 V 150 C ms KHz 2.5 10 3 Unit 0.1 450 CE PWM dimming frequency www.belling.com.cn 0.200 Max 2.5 Active, Vfb=1V, No Switching Switching Frequency RdsonH 0.190 Feedback Leakage current Quiescent Current Typ 2.5 Line Regulation Fsoc Min 50 BL8549 TYPICAL PERFORMANCE CHARACTERISTICS (Vin=3.6V, L=22uH, Cin=1uF, Cout=1uF, TA=25C, unless otherwise stated) Efficiency VS Output Current 100 95 95 90 90 85 85 80 80 Efficiency (%) Efficiency (%) Efficiency VS Iout for 10 LEDs 100 75 70 65 60 75 70 Vin=3.6V 55 6Pcs LED 8Pcs LED 50 Vin=4.2V 45 4Pcs LED 60 55 Vin=3.8V 50 65 10Pcs LED 45 40 40 0 10 20 30 40 50 0 10 Output Current (mA) 30 40 50 Output Current (mA) FB Voltage Vs. PWM Duty Cycle Frequency Vs. Vin for 10 LEDs 240 600 220 590 200 580 180 570 FB Voltage (mV) Switching Frequency (KHz) 20 560 550 540 530 160 140 120 100 80 60 520 40 510 20 0 500 2.5 3.0 3.5 4.0 4.5 0% 5.0 Vin (V) 20% 40% 60% 80% 100% PWM Duty (%) Switching waveform Vin=2.5V, 10 LEDs Switching waveform Vin=3.6V, 10 LEDs (CH1=Vin, CH2=Vout, CH3=SW, CH4=Isw) (CH1=Vin, CH2=Vout, CH3=SW, CH4=Isw) www.belling.com.cn 4 BL8549 Switching waveform Vin=4.2V, 10 LEDs Startup waveform Vin=3.6V, 10 LEDs (CH1=Vin, CH2=Vout, CH3=SW, CH4=Isw) (CH1=Vin, CH2=Vout, CH3=SW, CH4=Isw) FUNCTIONAL DECRIPTIONS Loop Operation The BL8549 is a high voltage, high-efficiency, DC-to-DC step-up LED driver, capable of driving up to 10 LEDs. It integrates with a 300m MOSFET, with external schottky diode. It uses a PWM current-mode control scheme. An error amplifier integrates error between the FB signal and the internal reference voltage. The output of the integrator is then compared to the sum of a current-sense signal and the slope compensation ramp. This operation generates a PWM signal that modulates the duty cycle of the power MOSFETs to achieve regulation for output voltage. Current Limit There is a cycle-by-cycle current limit on the high-side MOSFET of 1A(typ). When the current flowing out of SW exceeds this limit, the low-side MOSFET turns off and the external schottky diode rectifier turns on. Unlike the traditional method of current limiting by limiting the voltage at the external compensation node, which usually has large variation due to duty cycle variance, this type of peak current limiting scheme provides a relatively more accurate limit for output current, thereby lowering the requirements for system design. Light Load Operation Traditionally, a fixed current mode constant frequency PWM DC-DC regulator always switches even when the output load is small. When energy is shuffling back and forth through the power MOSFETs, power is lost due to the finite RDSONs of the MOSFETs and parasitic capacitances. At light load, this loss is prominent and efficiency is therefore very low. BL8549 employs a proprietary control scheme that improves efficiency in this situation by enabling the device into a power save mode during light load, thereby extending the range of high efficiency operation. PWM BRIGHTNESS DIMMING CONTROL at CE PIN When CE pin is forced a PWM signal with frequency higher than 5KHz, the chip is in dimming mode. The internal circuit changes the feedback voltage according to the duty cycle of the PWM signal. The feedback voltage (Vfb) is simply defined as below: Vfb=200mV x Duty Cycle (%) To shut down the chip, one has to make the CE signal low, and keep its low state for more than 2.5ms. www.belling.com.cn 5 BL8549 PACKAGE OUTLINE Package DFN2x2-6 Devices per reel 3000 Unit mm Devices per reel 3000 Unit mm Package specification： Package SOT23-6 Package specification： www.belling.com.cn 6