BL8516 1.2A Step-down DC-DC Converter DESCRIPTION FEATURES ◆ ◆ ◆ ◆ ◆ ◆ ◆ BL8516 is a current mode PWM step-down DC-DC converter, which has an internal 2A power switch. It has the wide input voltage range of 3.6V to 20V, so it can suit for regulating a wide variety of power source. Range of Input Voltage: 3.6V~20V Built-in NPN switch <1µA Shutdown Current Oscillation Frequency: 1.2MHz High efficiency: 90% High Accuracy Output Voltage: ± 2% Low Temperature-Drift Coefficient of Output Voltage: Type: ± 100ppm/°C ◆ Operating Temperature Range: -40℃ ~85℃ ◆ Demo Board Available BL8516 use bipolar technology and make of a PWM control circuit, a reference voltage unit, an error amplifier, a protection circuit, Chip Enable circuit, and under voltage lockout circuit. A low ripple, high efficiency step-down DC-DC converter can be easily composed of this IC with only several external components, or an inductor, a diode and capacitors. Output Voltage can be adjusted with external resistors. APPLICATIONS ◆ Power source for hand-held communication equipment, cameras, video instruments such as VCRs, camcorders. ◆ Power source for battery-powered equipment. ◆ Power source for household electrical appliance The BL8516 has the cycle-by-cycle current limit circuit; current limiting provides protection against shorted output. The low current (<1uA) shutdown provides complete output disconnect, enabling easy power management in battery powered systems. ORDERING INFORMATION PIN CONFIGURATION BL8516 1 2 3 Code Description Product Classification Temperature & Rohs: C: -40~85°C, Pb Free Rohs Std. Marking 1 2 3 Package Type: D8: SOP-8 HF XX YYBZZ Packing Type: TR: Tape & Reel (Standard) HF: Product Code XX: Output Voltage Adjustable YY: LOT NO. B: FAB Code ZZ: Date Code www.belling.com.cn 1 BL8516CD8TR 8 7 6 5 HFXX YYBZZ 1 2 3 4 BL8516 PIN DESCRIPTION Pin No. Symbol Description 1 BOOST 2 VIN Power Supply Pin 3 SW Switching Node: PWM output connection to inductor. 4 GND 5 FB Pin for Feedback Voltage 6 NC Not Connected 7 CE Chip Enable Pin (Active with “H”) 8 NC Not Connected Boost Pin Ground Pin BLOCK DIAGRAM ABSOLUTE MAXIMUM RATING Supply Voltage Boost Pin Voltage Boost Pin Above SW Pin CE Pin Voltage FB Pin Voltage Operating Ambient Temperature Range Storage Temperature Range Lead Temperature (Soldering, 10 sec) Thermal resistance: ΘJA www.belling.com.cn 25V 35V 25 –0.3V to Vin+0.3V –0.3V to 6V –25°C to 85°C –40°C to 150°C 260°C 150°C/W 2 BL8516 ELECTRICAL CHARACTERISTICS (Test condition is in 25ºC, VIN=12V, VBOOST=17V, unless otherwise noted.) Symbol Item Conditions Min. Typ. Max. VUVLO VFB IFB IQ △VFB/△V △VFB/△T FOSC_MAX FOSCTH DMAX ILIMIT Under voltage Lockout Feedback Voltage FB Pin Bias Current Quiescent Current Quiescent Current in Shutdown Reference Line Regulation Feedback Voltage Temperature Coefficient Oscillator Frequency Frequency Shift Threshold on FB Pin Max Duty Cycle 3.35 1.25 150 2 1.225 VFB=1.25V VFB=1.3V VCE=0V VIN=5V to 20V Unit 3.6 1.275 600 V V nA mA 2 uA 0.08 %/V ±100 ppm/℃ VFB=1.1V 1.2 MHz FSW=700K 0.44 V 88 % VIN=10V 2.5 A ISW=300mA 220 350 mV uA μA -25℃ ≤ Topt≤ 85℃ ISW ICEH Switch Current Limit Switch Saturation Voltage Switch Leakage Current CE “H” Input Current VCE =3V 6.5 1 15 ICEL CE “L” Input Current VCE = 0V 0.03 0.1 VCEH CE “H” Input Voltage VIN = 12V μA V VCEL CE “L” Input Voltage VIN = 12V 0.4 V VCESAT 1.8 TYPICAL APPLICATION C3 L1 VOUT CE D3 VIN BOOST VIN SW GND C1 D1 NC CE NC FB R1 C2 U1 R2 www.belling.com.cn 3 BL8516 DEMO BOARD BOM Table 1 Bill of Materials No. Reference Type Specification Note 1 C1 Capacitor Tantalum Capacitor; 25V/47uF; SMD 2 C2 Capacitor Tantalum Capacitor; 25V/22uF; SMD 3 C3 Capacitor MLCC 10nF; SMD 0805 4 D1 Diode SS34; 40V, 3A; SMD 5 D3 Diode 1N4148; 75V; 100mA; SMD 1206 6 L1 Inductor 10uH; 3A; SMD, Shielding 7 IC1 IC BL8516; SMD SOP-8 8 R1 Resistor SMD 0805; 1% Note 1 9 R2 Resistor SMD 0805; 1% Note 1 Note1: For VOUT=5V, R1 is 9.1K and R2 is 3K. For VOUT=3.3V, R1 is 3.3K and R2 is 2K. DEMO BOARD MEASUREMENT Load Regulation (VOUT=5V) Efficiency vs. Load Current (VOUT=5V) 5 Efficiency(%) Output Voltage(V) 6 4 3 2 1 0 0 200 400 600 800 1000 100 90 80 70 60 50 40 30 20 10 0 0 1200 200 400 Output Current(mA) VIN=7V VIN=12V VIN=7V VIN=20V Load Regulation (VOUT=3.3V) Efficiency(%) Output Voltage(V) 3 2 1 0 200 400 600 www.belling.com.cn VIN=12V 1000 1200 VIN=12V VIN=20V 800 1000 100 90 80 70 60 50 40 30 20 10 0 0 1200 200 400 600 800 1000 Output Current(mA) Output Current(mA) VIN=7V 800 Efficiency vs. Load Current (VOUT=3.3V) 4 0 600 Output Current(mA) VIN=7V VIN=20V 4 VIN=12V VIN=20V 1200 BL8516 Feedback Voltage vs.Supply Voltage Quiescent Current vs. Supply Voltage 1.30 Feedback Voltage(V) Quiescent Current(uA) 3000 2000 1000 0 1.28 1.26 1.24 1.22 1.20 0 5 10 15 20 5 10 Feedback Voltage vs.Temperature 20 Frequency vs.Temperature 1.30 1.30 1.28 1.25 Frequency(MHz) Feedback Voltage(V) 15 Supply Voltage(V) Supply Voltage(V) 1.26 1.24 1.22 1.20 1.15 1.10 1.05 1.20 1.00 -50 -25 0 25 50 75 100 -50 Temperature -25 0 25 50 75 100 Temperature(ºC) APPLICATION INFORMATION ∆IL = (1 – D)(VOUT + VD)/(L • FOSC) In which FOSC is the switching frequency and L is the value of the inductance. The average inductor current is equal to the output current and the peak inductor current is the sum of the output current and one half of the ripple current: ILPK = IOUT + ∆IL /2 This current has to be kept below the maximum allowed switch current (ILIMIT) for output regulation. Typical values of ILIMIT are above 2.5A and the maximum output current is IOUT (MAX) = ILIMIT – ∆IL/2 If the ripple current is small, then the available output current is close to the switch current limit. It is recommended that the inductor value be chosen such that the peak- Inductor Selection and Maximum Output Current The duty cycle of the internal switch is: D = (VOUT + VD)/(VIN – VSW + VD) In which VD is the forward voltage drop of the catch diode (D1) and VSW is the voltage drop of the internal switch. The value of duty cycle at full load current is of special interest, when values of VSW and VD can both assumed to be 0.4V. Since BL8516 has a maximum guaranteed duty cycle of 88%, the minimum input voltage is limited for a particular value of output. When the switch is off, the voltage drop across the inductor is equal to output voltage plus the catch diode drop. Therefore the peak-to-peak ripple current in the inductor can be derived: www.belling.com.cn 5 BL8516 to-peak inductor ripple current is equal to one third of switch current limit. Hence the value of inductance and the maximum output current can be expressed as: L = 3(1 – D)(VOUT + VD)/(ILIMIT • FOSC) and IOUT (MAX) = (5/6) ILIMIT From above discussion it is derived that the switch current limit is dependant on the duty cycle, which also is a function of input voltage. For a specific application, one can calculate the value of inductance and the range of available output current according to the maximum and minimum allowed input voltage values. large output capacitance. The above equation also offers a good starting point for obtain the proper output capacitance value to achieve satisfactory performance. Application engineers can start with the datasheet recommended value. The high performance (low ESR), small size and robustness of ceramic capacitors make them the preferred type for BL8516 applications. One needs keep in mind that not all ceramic capacitors are the same. Many of the higher value capacitors use poor dielectrics with high temperature and voltage coefficients. Catch Diode Schottky diode with 3A current rating is recommended for the catch diode D1. Capacitor Selection The input capacitor (C1) supplies the AC component of the current drawn by the converter. A 10uF ceramic capacitor is sufficient in most cases. In case the application circuitry has relatively large parasitic parameters (most often caused by long wires or filter components), additional bulk input capacitance may be required. For high-power applications it is suggested to increase the input capacitance to 100uF. The output capacitor filters the square wave generated by the chip to produce the DC output and stores energy to supply transient loads as well as stabilizes the control loop. While for most switching mode converters, the output ripple is mainly determined by the equivalent series resistance (ESR) of the output capacitor, the BL8516’s control loop is independent on the output capacitor’s ESR for stable operation. If a low ESR capacitor is selected, for example ceramic capacitor, Output ripple can be estimated by the following equation: VRIPPLE = ∆IL• [ESR+1/(8• FOSC•C2)] The output capacitor must have an energy capacity larger than the inductor-otherwise the transfer of energy from the inductor to the output can cause large overshoot. For a 5% overshoot, the minimum value of the output capacitor can be presented as: BOOST Pin Considerations In the application circuit shown in the cover page, capacitor C3 and diode D2 are used to boost input voltage to a higher level. In most cases a 10nF capacitor and a fast switching diode are suitable for this purpose. The voltage at the BOOST pin must be at least 2.5V higher than the SW pin for best efficiency. The minimum operating voltage of an BL8516 application is limited by the under voltage lockout (< 3.6V) and by the Maximum duty cycle as outlined above. For proper startup, the boost circuit also limits the minimum input voltage. If the input voltage is ramped slowly, or the BL8516 is turned on with its CE pin when the output is already in regulation, then the boost capacitor may not be fully charged. Because the boost capacitor is charged with the energy stored in the inductor, the circuit will rely on some minimum load current to get the boost circuit running properly. This minimum load will depend on input and output voltages, and on the arrangement of the boost circuit. The minimum load generally goes to zero once the circuit has started. In many cases the discharged output capacitor will present a load to the switcher, which will allow it to start. C 2 ≥ 10 • L • ( ILIMIT / VOUT ) 2 Good transient performance also requires www.belling.com.cn 6 BL8516 PACKAGE LINE Package SOP-8 Devices per reel 2500Pcs Unit mm Package specification： Symbol Dimension (mm) MIN NOM MAX A - - 1.77 A1 0.08 0.18 A2 1.2 A3 Symbol Dimension (mm) MIN NOM MAX D 4.7 4.9 5.1 0.28 E 5.8 6 6.2 1.4 1.6 E1 3.7 3.9 4.1 0.55 0.65 0.75 e b 0.39 - 0.48 L b1 0.38 0.41 0.43 L1 c 0.21 - 0.26 θ www.belling.com.cn 7 1.27BSC 0.5 0.65 0.8 1.05BSC 0 - 8°