BL8545 REV1.0-Revised SEP 2008 High Efficiency Low Noise PFM Step-up DC/DC Converter DESCRIPTION The BL8545 PFM step-up Converter drives white LEDs with a constant current to provide backlight in cell phones, PDAs, and other handheld devices. It features allowing series connection of the white LEDs so that the LED currents are identical for uniform brightness. An enable input can be pulsed repeatedly to adjust LEDs brightness. The fast 500KHz to 2MHz operation frequency allows for smaller capacitor and inductor. Fault condition protection uses cycle-by cycle current limiting to sense maximum inductor current and over-voltage protection. The 0.2V low reference voltage minimized the power loss across the current sense resistor. FEATURES • • • • • • • • • Up to 24V Output Voltage Wide Operation Range: 2V to 6V Maximum 2MHz Operating Frequency PWM Dimming Control Shutdown Current <1uA Current Limit Cycle-by-Cycle Low Current Sense Threshold: 200mV 24V Over Output Voltage Protection Compact SOT23-6 Package APPLICATIONS The converter can operate from 2V to 6V, and capable of delivering maximum 200mA output current at 4-LEDs application with 3V input voltage. Quiescent current drawn from power source is as low as 120uA. All of these features make BL8545 be suitable for the portable devices, which are supplied by a single battery. • • • Compact Back Light Module Power Source for LED Constant Current Source BL8545 is available in SOT23-6 package that is PB free. TYPICAL APPLICATION D1 L1 10uH VIN SS14 LED1 LED17 LED2 Cin Cout 4.7uF 4.7uF VIN ON OFF LED18 LED3 LX OVP LED19 LED4 LED20 BL8545 LC3300 CE FB GND R1 Figure1. BL8545 Typical Application Circuit www.belling.com.cn 1 R5 BL8545 PIN CONFIGURATION 6 5 4 LE: Product Code LEBZZ B: 1 2 3 FAB Code ZZ: Date Code SOT23-6 (Top View) PIN DESCRIPTION Pin No. Symbol Description 1 LX 2 GND 3 FB Pin for Feedback Voltage 4 CE Chip Enable Pin (Active with “H”) 5 OVP Over Voltage Protection 6 VIN Power Supply Pin Switching Pin Ground Pin BLOCK DIAGRAM www.belling.com.cn 2 BL8545 ABSOLUTE MAXIMUM RATING Parameter Value Max Input Voltage CE Pin Voltage Lx Pin Output Current Lx Pin Voltage Operating Junction Temperature (TJ) Ambient Temperature (TA) Power Dissipation SOT-23-6 Storage Temperature (Ts) Lead Temperature & Time -0.3V to 8V -0.3V to (Vin+0.3V) 1.6A 24V 125°C -40°C to 85°C 250mW -40°C to 150°C 260°C, 10Sec ELECTRICAL CHARACTERISTICS (Ta=25ºC，VIN=3V，VCE=3V, unless otherwise noted) Symbol Item Conditions VIN VFB IFB Operating Input Voltage Feedback Voltage FB Pin Bias Current IQ Quiescent Current FOSC_MAX ILimit VCESAT ILX VCEH VCEL ICE VOVP Maximum switching Frequency Switching Current Limit Switch VCESAT Switching pin Leak Current CE Voltage High CE Voltage Low CE Pin Bias Current Over Voltage Protection Min. 2 0.190 10 VFB=0.3V VCE=0V VFB=0V ILX=300mA VLX=5V VCE=0 to 3V VCE=3 to 0V Typ. 0.200 45 93 0.4 2 1.6 260 0.11 Max. Unit 6 0.210 100 120 1.0 V V nA uA uA MHz A mV uA V V uA V 1.5 0.4 18 24 TYPICAL PERFORMANCE CHARACTERISTICS CE Pin Current vs. Temperature (VIN=VCE)) 80 70 60 50 40 30 20 10 0 50 CE Pin Current(uA) CE Pin Bias Curren(uA) CE Pin Bias Current vs. EN pin Voltage (VIN=VCE) 40 30 20 10 0 -50 0 1 2 3 4 5 0 25 50 75 Temperature 6 CE Pin Voltage(V) www.belling.com.cn -25 VCE=2.5V 3 VCE=3V VCE=6V 100 BL8545 Quiescent Current vs. Supply Voltage (VCE=VIN,VFB=0.3V) Quiescent Current(uA) Quiescent Current(uA) Quiescent Current vs. Supply Voltage (VCE=0V) 1.0 0.8 0.6 0.4 0.2 0.0 0 1 2 3 4 5 120 100 80 60 40 20 0 0 6 1 2 0.220 0.200 0.180 0.160 0.140 0.120 3 4 5 6 75 100 FB Pin Voltage vs. Temperature FB Pin Voltage(V) FB Pin Voltage(V) FB Pin Voltage vs.Supply Voltage 2 3 Supply Current(V) Supply Voltage(V) 4 5 0.220 0.200 0.180 0.160 0.140 0.120 6 -50 -25 0 Supply Voltage(V) 25 50 Temperature(ºC) Efficiency vs. Output Current (4LEDs) Maximum Output Currenr vs. Output Voltage Maximum Output Currenr(mA) Efficiency(%) 600 100 80 60 40 20 0 0 20 40 60 80 100 500 400 300 200 100 0 120 0 Output Current(mA) VIN=2.5V VIN=3V Switch Frequency(MHz) Switch Frequency(MHz) 2 1 0 5 25 30 VIN=3V VIN=6V 2.0 1.5 1.0 0.5 0.0 -50 6 -25 0 25 50 Temperature(ºC) Supply Voltage(V) www.belling.com.cn 20 Switch Frequency vs. Temperature (4LEDS*100mA) 3 4 15 VIN=2.5V VIN=6V 4 3 10 Output Voltage(V) Switch Frequency vs. Supply Voltage (4LEDs*100mA) 2 5 4 75 100 BL8545 APPLICATION INFORMATION Dimming Control 1. Using a PWM Signal to CE Pin When adding the PWM signal to CE pin, the BL8545 is turned on or off by the PWM signal, so the LEDs operate at either zero or full current. The average LED current increase proportionally with the duty cycle of the PWM signal. The frequency range of the PWM signal is from 1 kHz to 300KHz. 2. Using a DC Voltage From the Figure 2, we can add a DC voltage to FB pin, we adjust the LED current by changing the DC voltage, which control the brightness, DC voltage range is from 0V to 2V. LED1 LED2 LC3300 BL8545 LED3 FB VDC R13 R12 90K R1 5K 10 Figure 2. Dimming Control Using a DC Voltage 3. Using a Filtered PWM Signal The filtered PWM signal can be considered as an adjustable DC voltage. It can be used to replace the variable DC voltage source in dimming control. The circuit is shown in Figure 3. LED1 LED2 LC3300 BL8545 LED3 FB PWM R14 R13 R12 90K 5K C12 0.1uF R1 10 Figure 3. Dimming Control Using a Filtered PWM Signal www.belling.com.cn 5 BL8545 PACKAGE INFORMATION Package Type SOT-23-6 Number of Devices per reel Package specification： www.belling.com.cn 3000 Unit: mm 6