BL8542 REV1.0, May 2009 0.85V startup, 1MHz, 300mA Iout, Synchronous Boost Converter DESCRIPTION FEATURES The BL8542 is a step-up converter that provides a boosted output voltage from a low voltage source. Because of its proprietary design, it starts up at a very low input voltage down to 850mV, making it an ideal choice for single cell alkaline/NiMH battery operations. •• •• A switching frequency of 1MHz minimizes solution footprint by allowing the use of tiny, low profile inductors and ceramic capacitors. The current mode PWM design is internally compensated, reducing external parts count. •• •• •• •• •• •• •• •• Up to 95% Efficiency 1MHz Switching Frequency allows small inductor and output cap Input boost-strapping allows using small or no input cap Low Vin Start-up Voltage down to 850mV Ideal for Single Alkaline Cell operations Maximum Output Current up to 300mA Low Noise PWM control Internally Compensated Current Mode Control Internal Synchronous Rectifier Logic Control Shutdown (IQ<1uA) Available in SOT23-5 BL8542 is housed in a tiny SOT23-5 Package APPLICATIONS TYPICAL APPLICATION CIRCUIT •• •• •• •• •• One to Three Cell Battery Operated Devices Medical Instruments Bluetooth Headsets Flash-Based MP3 Players Noise Canceling Headphones PIN CONFIGURATION NOTE: Input capacitor (Cin=0.47uF) and Output capacitor (Cout≥4.7uF) are recommended in all application circuit. ORDERING INFORMATION Product Code Package Devices per Reel Top Marking BL8542CB5TR SOT23-5 3000 AAZZ 上海贝岭股份有限公司 www.belling.com.cn 1 BL8542 BLOCK DIAGRAM OUT EN Low Input startup osc Reference + GM FB - + Comparator Logic SW Driver - + G DETAIL DESCRIPTION APPLICATION INFORMATION BL8542 is a low input voltage start up, current mode dc-dc step up converter. It’s operation can be best understood by referring to the block diagram. Upon star ting up, the low voltage star tup circuitry drives SW with on-off cycles, transferring energy from input to OUT by storing energy in the inductor during on-time and releasing it to the output during off-time. When OUT reaches 2V, the startup circuit turns off and the main controller takes over. The main control loop consists of a reference, a GM error amplifier, a PWM controller, a current sense amplifier, an oscillator, a PWM logic control, and it is power stage including its driver. The main control loop is a classic current mode control loop. The GM stage integrates the error between FB and REF, and its output is used to compare with a triangular wave which the summing result of the current sense amplifier output and a slope compensation voltage. The output of the comparator is used to drive the power stage to reach regulation. Output Voltage selection The output voltages can be set by connecting FB to OUT, to G or to the midpoint of a resistor divider connected to OUT. See below table for details. FB=G VOUT =5.0V FB=OUT VOUT =3.3V FB to resistor divider VOUT=0.6V(1+R1/R2) Inductor selection With switching frequency up to 1MHz, small surface mount inductors can be used with values from 2.2uH to 4.7uH. For a given chosen inductor value and application conditions make sure the peak inductor current does not exceed the maximum current rating of the selected vendor's inductor. Input and output capacitor selection The BL8542's bootstrap architecture allows the use of very small input capacitor. For applications that only need to drive small output load current, the input capacitor is optional, because once output is started up, the IC's is powered by OUT, a quiet power supply. The output capacitor is used to stabilize the loop and provide ac current to the load. A low ESR ceramic cap with values from 2.2uF to 22uF can be used. Smaller value capacitors are generally cheaper with small footprints, while larger capacitor provides lower ripples and better transient load responses. Also, when extreme low startup voltage is needed, larger output capacitors are needed for the part to startup under heavy load condition. 上海贝岭股份有限公司 www.belling.com.cn 2 BL8542 ABSOLUTE MAXIMUM RATING Parameters Value SW Voltage -0.3 ~ 6 V EN, FB, OUT Voltage -0.3 ~ 6 V Juntion to Ambient Thermal Resistance 190 oC/W Maximum Power Dissipation 0.45 W Operating Temperature Range -40 ~ 150 oC Storage Temperature -55 ~ 150 oC IR Reflow Lead Temperature and Time 260oC , 10s Note: Exceed these limits to damage to the device. Exposure to absolute maximum rating conditions may affect device reliability. ELECTRICAL CHARACTERISTICS o Test condition: Vin=1.8V, Vout=3.3V, TA=25 C, unless otherwise specified. Parameters Condition Min. Typ. Minimum Input Voltage 0.7 Startup Voltage 0.85 Dropout Voltage, Vout≥2.8V FB Feedback Voltage FB=OUT FB=G Vout=2.5 to 5V Max. Unit V 1.1 V 3.3 V 5 V 0.6 V FB Input Current 50 nA 5 V Output Voltage Range External divider Quiescent Current at OUT Vfb=0.7V 25 Shutdown Supply Current at OUT EN=G 0.1 NMOS Switch On Resistance Isw=100mA 0.3 ohm PMOS Switch On Resistance Isw=100mA 0.7 ohm NMOS Switch Current Limit SW Leakage Current 2.5 1 1 Vout=5.5V, Vsw=0 or 5.5V, EN=G EN Input Current EN Input Voltage for “Low” EN Input Voltage for “High” uA 0.6 uA A 1 uA 1 uA 0.3 V V 上海贝岭股份有限公司 www.belling.com.cn 3 BL8542 TYPICAL PERFORMANCE CHARACTERISTICS o Typical values are tested at TA=25 C, unless otherwise specified. Efficiency vs. Output Current Efficiency vs. Output Current (Vout=3.3V; Ta=25℃) (Vout=5V; Ta=25℃) 100 100 V IN=2.4V 90 V IN=1.2V 80 80 Efficiency(%) 70 Efficiency(%) VIN=2.4V 90 VIN=1.8V 60 50 VIN=1.8V 70 V IN=1.2V 60 50 40 40 30 30 20 20 1 10 100 1 1000 10 Output Voltage vs. Output Current ( Vout=3.3V;Ta=25℃) 100 1000 Output Current(mA) Output Current(mA) Minimum Start-Up Voltage vs. Output Current (Vout=3.3V，Ta=25℃) 3.25 2 1.8 Start-up Voltage(V) Output Voltage(V) 3.2 VIN=1.2V 3.15 VIN=1.8V VIN=2.4V 3.1 3.05 1.6 1.4 1.2 1 0.8 3 0 50 100 150 200 250 300 350 400 0.6 450 0 Output Current(mA) 20 40 60 80 100 120 140 160 Output Current(mA) No Load Input Current vs. Inpout Voltage ( VOUT=3.3V；Ta=25℃；No load) Maximum Output Current vs. Input Voltage (L=4.7uH，Ta=25℃) 400 700 300 VOUT=3.3V 500 Input Current(uA) Maximum Output Current(mA) 350 600 400 VOUT=5V 300 200 250 200 150 100 100 50 0 0.5 1 1.5 2 2.5 Input Voltage(V) 3 3.5 4 0 1.5 1.8 2.1 2.4 2.7 3 Input Voltage(V) 上海贝岭股份有限公司 www.belling.com.cn 4 BL8542 TYPICAL PERFORMANCE CHARACTERISTICS cont' o Typical values are tested at TA=25 C, unless otherwise specified. VREF(T)/VREF(T=20℃) vs. Temperature Output Voltage vs. Temerature 1.006 3.25 1.002 3.24 0.998 3.23 Output Voltage(V) Normalized VREF 1.01 0.994 0.99 0.986 0.982 3.22 3.21 3.2 3.19 0.978 3.18 0.974 3.17 0.97 -45 -45 -25 -5 15 35 55 75 95 Temerature(℃) -25 -5 15 35 55 75 95 Temerature(℃) Frequency vs. Temperature 1100 Frequency(kHz) 1000 900 800 700 600 -45 -25 -5 15 35 55 75 95 Temperature(℃) 上海贝岭股份有限公司 www.belling.com.cn 5 BL8542 PACKAGE OUTLINE DIMENSION Package Devices per reel SOT23-5 3000 Dimension (mm) 上海贝岭股份有限公司 www.belling.com.cn 6