KB4312 Kingbor Technology Co.,Ltd TEL:(86)0755-26508846 FAX:(86)0755-26509052 Tiny Package, High Performance, Constant Current Switching Regulator for White LED Very Low Cost DESCRIPTION FEATURES The KB4312 step-up converter drives white LEDs with a constant current to provide backlight in cell phones, PDAs, and other hand-held 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 LED’s brightness. The fast 1.2 MHz current-mode PWM control allows for smaller capacitor and inductor. Fault condition protection uses cycle-by-cycle current limiting to sense maximum inductor current, thermal protection and over-voltage protection. Also included soft-start eliminates inrush current during start-up. The 0.24V low reference voltage minimized the power loss across the current-setting resistor. •Operating Voltage:2.5V~6.5V •High Operating Frequency: 1.2MHz •High Efficiency: Up to 92% •High Output Voltage: Up to 28V(max) •Shutdown Current <1PA •18V Output Over-voltage protection (ADJ) •Digital Dimming Control. •Built-in Cycle-by Cycle Current-limiting. •Built-in Soft-Start Function. •0.24V Low Reference Voltage(+/-5%) •Tiny SOT23 Package The KB4312 is available in SOT23 packages / APPLICATIONS • LED Module • LED Backlight for LCD Display (1” ~6.5 ” ) • Constant Current Source! SIMPLIFIED BLOC DIAGRAM VIN 6 EN ON/OFF Control Logic / PWM Dimming Control 4 1 VREF 0.240V LX Soft-Start VBG 1.27V CTL N + Control Logic FB 3 OVP 5 17V KB4312B FB=240mV KB4312A FB=1.27V VBG + Current Limit 0.25A Overvoltage Protection + - - CTL 2 GND REV: 3.2 1 KB4312 Kingbor Technology Co.,Ltd TEL:(86)0755-26508846 FAX:(86)0755-26509052 PIN CONFIGURATION SOT23-6 SOT23-6 SOT23-5 LX 1 6 VIN GND 2 5 OVP FB 4 EN 3 SOT23-5 LX 1 5 VIN 4 EN GND 2 FB KB4312B FB=240mV 3 KB4312A FB=1.27V ORDER INFORMATION Part number Package KB4312A- GRE SOT23-5, Green Part number SOT23-6, Green PIN DESCRIPTION Symbol LX GND ATxxxx, xxxx: Date Code Package KB4312B- GRE Pin N0. 1 2 Marking I/O I P 3 FB I 4 EN I 5 6 OVP VIN I P Marking 5121x, x: Date Code 5121m,Date Code with one bottom line Description Step-up Regulator N-MOS Drain. Place output diode and inductor. Ground Step-Up Regulator Feedback Input. Connect a sense resistor from FB to ground. (KB4312B FB=240mV,KB4312A FB=1.27V) Enable and Dimming Control Input. LED brightness and IC shutdown are controlled by the voltage on EN. Driving low for longer than 4ms to shutdown the IC. Over-voltage protection input(ADJ) Power supply. ABSOLUTE MAXIMUM RATINGS (Note 1) Parameter VIN voltage LX , OVP voltage EN , FB to GND Switch Current (ILX) Continuous power dissipation (SOT23-6 Ta=+25 OC) Operating Junction Temperature Range Lead Temperature (Soldering 5 sec) Storage Temperature Package Thermal Resistance (ӘJA) ESD Susceptibility (HBM) ESD Susceptibility (MM) Rated Value -0.3 to +6.5 -0.3 to +28 -0.3 to +6.5 0.25 0.35 -35 to 85 260 -65 to 125 250 2 200 Unit V V V A W к к к к/W KV V Note1:Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Exposure to absolute maximum rating conditions for extended periods may affect device reliability 2 KB4312 Kingbor Technology Co.,Ltd TEL:(86)0755-26508846 FAX:(86)0755-26509052 RECOMMENDED OPERATION CONDITIONS Parameter Power supply voltage Operating temperature Symbol Values Typ. ѧ +25 Min. 2.5 -30 VIN Top Unit Max. 6.5 +85 V к ELECTRICAL CHARACTERISTICS (VIN=2.5V, Ta=+25к, unless otherwise noted) Parameter Operating V IN Range Symbol Test Condition VIN input Voltage VIN Under Voltage Thershold No Load Current Shutdown Current Feedback Reference (+/-5%) Feedback Reference (+/-2%) Over-voltage Threshold Over-voltage Hysteresis OVP Leakage Current UVLO I IN1 IIN3 V FB V FB VOVP IOVP Output Voltage Line Regulation Switching Frequency Maximum Duty Soft-Start charging time Switching Current Limit LX ON Resistance LX Leakage Current EN Input Current EN Input Level EN low Shutdown Delay EN Low Cycle Time EN High Cycle Time fOSC DMAX tSS ILX RLX ILeakage IEN VIH VIL tCYCL tCYCH Min. 2.5 Typ. Max. Units - 6.5 V VIN falling, 100mV hysteresis 1.4 1.5 1.6 V No Switching , FB>0.2V 1 3 mA EN=0V 1 uA KB4312B 0.225 0.240 0.255 V 1.245 1.270 1.295 V KB4312A 16 17 20 V KB4312B 2 V EN=0V 1 uA 2.5V< VIN <6.0V 0.1 % VIN=3.0V,duty cycle=80% , VIN =2.5V, ILX =750mA VLX =16V, EN=0V EN=5V Note(1) Note(1) 0.5 0.05 1.5 0.05 0.05 0.8 90 0.2 0.15 0.40 4 1.0 1 1 0.4 4 4 MHz % ms A Ө uA uA V V ms ms ms Note(1): tCYCL and tCYCH are included rising time and falling time of PWM signal. Recommended PCB Layout KB4312B 3 KB4312 Kingbor Technology Co.,Ltd TEL:(86)0755-26508846 FAX:(86)0755-26509052 TYPICAL PERFORMANCE CHARACTERISTICS Quiescent Current 2.2 –50qC 2.0 1.8 25qC 1.6 100qC 1.4 350 1.2 300 1.4 1.0 SHDN = 10V 250 1.2 0.8 200 1.0 0.6 150 0.8 0.6 SHDN = 3.6V 100 0.4 50 0.2 0 Switching Frequency SHDN Pin Bias Current 400 0 2 4 VIN (V) 6 8 0.4 0.2 SHDN = 2.7V 0 – 50 Feedback Bias Current SHDN = 3V – 25 0 50 25 TEMPERATURE (qC) 75 100 85 50 –25 50 25 0 TEMPERATURE (qC) 75 100 Current Limit vs Duty Cycle Efficiency vs Temperature 60 350 VIN = 3.6V 3 LEDs 300 ILED = 20mA 84 250 40 83 ILED = 15mA 82 ILED = 10mA 200 30 150 20 100 81 10 0 –50 0 –50 –25 50 25 0 TEMPERATURE (qC) 75 100 80 –50 50 0 0 50 TEMPERATURE (qC) 100 0 20 40 60 DUTY CYCLE (%) 80 100 4 Kingbor Technology Co.,Ltd KB4312 TEL:(86)0755-26508846 FAX:(86)0755-26509052 APPLICATION CIRCUIT Vin=2.7~6V VOUT=6~24V 10uH 1N5819 1uF 1uF 1 LX 6 VCC OVP 5 KB4312B PWM or ON/OFF 4 EN FB 3 GND 2 20MA 240mV Rset 12R~51R Figure 1a.KB4312 For 2 to 6 LEDs Back Light Unit.(Step-Up) BAT54s 2.2K 1 1uF -10V 3 2 1uF Vin=2.7~6V 10V 10uH 10uF VOUT +15V (15mA) 1N5819 1uF 10uF R1 510K 1 LX 5 VCC FB 3 1.27V KB4312A 4 EN ON/OFF R1= ( VOUT 1.27V R2 47K GND 2 2.2K 1 1uF -1 ) x R2 -10V 3 2 1uF BAT54s Vin=5~20V 1uF 10uH 10V 1 3 VOUT +15V(15mA) 2 1K 1uF 1uF 5.1V 10uF 1 LX R1 510K 5 VCC R1= ( VOUT -1 ) x R2 1.27V FB 3 1.27V KB4312A ON/OFF 4 EN GND 2 10uF R2 47K 5 Kingbor Technology Co.,Ltd TEL:(86)0755-26508846 FAX:(86)0755-26509052 KB4312 Function Description The KB4312 is a high efficiency and constant current DC-DC converter IC which is designed primarily for use in LED module applications. The output voltage of the step-up converter can be set from Vin to 28V with external sense resistor. The device suits to drive series-connected LEDs and provides even illumination by sourcing the same output current through each LED. KB4312 also consists of a logic shutdown , cycle-by-cycle current-limited , soft-start functions. Logic control input or PWM duty cycle control allows easy adjustment of LEDs brightness and on/off control. The average LED current is proportionable the duty-cycle of the PWM signal. Typical PWM frequency should be between 100Hz and 1kHz. The boost converter operates in current-mode PWM and a constant frequency of 1.2 MHz. Depending on duty cycle of each switching cycle can regulate output voltage. On the rising edge of the internal clock , the control and driver logic block sets internal flip-flop when the output voltage is too low, which turns on the N-MOS. The external inductor current ramps up linearly, storing energy in a magnetic filed. Once peak current of inductor over trans-conductance output level , the N-MOS turns off, the flip-flop resets, and external schottky diode turns on. This forces the current through the inductor to ramp back down, transferring the energy stored in the magnetic field to the output capacitor and LEDs. To reduce external component amount , the device will be built-in internal loop compensation. ʳ Enable Control Digital logic of EN provides an electrical ON/OFF control of the power supply. Connecting this pin to ground or to any voltage less than 0.4V and sustain the level over 4ms will completely turn off the regulator. In this state, current drain from the input supply is less than 1uA, the internal reference, error amplifier, comparators, and biasing circuitry turn off . If holding time of low level is less than 3ms on this pin, then the device only shutdown driver logic block. ʳ Dimming Control Digital logic of EN also provides LEDs brightness control by applying a PWM signal on EN pin. With this way, the LEDs operate with either zero or full current . The average LED current is proportional to the duty-cycle of the PWM signal. Typical PWM frequency should be between 100Hz and 1kHz. Output current is given by: I LED 105mV u TON PWM ʳ RSENSE u TS PWM Where: TON-PWM : On time of PWM signal TS-PWM : A cycle time of PWM signal If dimming control is not required , EN works as a simple on/off control. Drive EN high to enable the device , or drive EN low for shutdown. ʳ 6 Kingbor Technology Co.,Ltd TEL:(86)0755-26508846 FAX:(86)0755-26509052 KB4312 Soft-Start Soft-start allows a gradual increase of the internal current-limit level for the step-up converter during power-up to reduce input surge currents. As the internal current source charges the internal soft-start capacitor, the peak N-MOS current is limited by the voltage on the capacitor. In another story, when toggle or a logic-level transition on EN pin from low to high, soft-start function must work to enable constant current charging internal capacitor. When soft-start process has finished or appeared falling edge of PWM signal on EN pin , soft-start capacitor must be discharged to ground level. Cycle-by-Cycle Over-Current Protection The KB4312 provides cycle-by-cycle over-current protection. Current limit is accomplished using a separate dedicated comparator. The cycle-by-cycle current limit abbreviates the on-time of the N-MOS in event that the current of flowing N-MOS is greater than the current limit value. The current-limit feature protection against a hard short or over-current fault at the output. Over-Voltage Protection If VOVP is above 17V or LEDs are disconnected from the circuit, the FB pin is similar to pull down to ground with a sense resistor. This will cause N-MOS to switch with a maximum duty cycle and come out output over-voltage. This may cause the LX pin voltage to exceed its maximum voltage rating to damage built-in N-MOS. In the state, the OVLO protection circuitry stops the internal N-MOS . Power dissipation consideration The KB4312 maximum power dissipation depends on the thermal resistance of the IC package and circuit board, the temperature difference between the die junction and ambient air, and the rate of any airflow. The power dissipation in the device depends on the operating conditions of the regulator. The step-up converter dissipates power across the internal N-MOS as the controller ramps up the inductor current. In continuous condition, the power dissipated internally can be approximated by : Pboost [( I O u VO 2 1 Vin u D 2 ) ] u RDS (ON ) u D ) ( Vin 12 f OSC u L where IO : It is the load current. fOSC : It is a switching frequency. 7 Kingbor Technology Co.,Ltd TEL:(86)0755-26508846 FAX:(86)0755-26509052 KB4312 Applications Information External components of main boost converter can be designed by performing simple calculations. It need to follow regulation by the output voltage and the maximum load current, as well as maximum and minimum input voltages. Begin by selecting an inductor value. Once L is know, choose the diode and capacitors. Boost inductor Inductor selection depends on input voltage, output voltage, maximum current , switching frequency and availability of inductor values. The following boost circuit equations are useful in choosing the inductor values based on the application. They allow the trading of peak current and inductor value while allowing for consideration of component availability and cost. The peak inductor current is given by: I Lpeak I LAVG I LAVG IO 1 D 'I L 2 where: ϦIL is the inductor peak-to-peak current ripple and is decided by: 'I L Vin D u L f OSC D is the MOSFET turn on ratio and is decided by: D VO V in VO fOSC is the switching frequency. The inductor should be chosen to be able to handle this current and inductor saturation current rating should be greater than IPEAK. Diode selection The output diode has average current of IO, and peak current the same as the inductor’s peak current and a voltage rating at least 1.5 times the output voltage. Schottky diode is recommended and it should be able to handle those current. Output Capacitor The KB4312 is specially compensated to be stable with capacitors which have a worst- case minimum value of 1uF at the particular VOUT being set. Output ripple voltage requirements also determine the minimum value and type of capacitors. Output ripple voltage consists of two components the voltage drop caused by the switching current through the ESR of the output capacitor and the charging and discharging of the output capacitor: V RIPPLE I LPEAK u ESR VO Vin IO u VO C OUT u f OSC For low ESR ceramic capacitors, the output ripple is dominated by the charging or discharging of the output capacitor. 8 KB4312 Kingbor Technology Co.,Ltd TEL:(86)0755-26508846 FAX:(86)0755-26509052 PACAGE DESCRIPTION PACKAGE OUTLINE PAD LAYOUT DETAILS Small Outline SOT23-6 e b L E1 E a e1 D A 2 DATUM A C A2 A1 CONTROLLING DIMENSIONS IN MILLIMETRES APPROX CONVERSIONS INCHES. PACKAGE DIMENSIONS Millimetres Inches Millimetres DIM Inches DIM Min Max Min Max Min Max Min Max A 0.90 1.45 0.35 0.057 E 2.60 3.00 0.102 0.118 A1 0.00 0.15 0 0.006 E1 1.50 1.75 0.059 0.069 A2 0.90 1.30 0.035 0.051 L 0.10 0.60 0.004 0.002 b 0.35 0.50 0.014 0.019 e 0.95 REF 0.037 REF C 0.09 0.20 0.0035 0.008 e1 1.90 REF 0.074 REF D 2.80 3.00 0.110 0.118 L 0° 10° 0° 10° Small Outline SOT23-5 PACKAGE OUTLINE PACKAGE DIMENSIONS Millimeters Inches DIM MIN. MAX. MIN. MAX. 0.90 1.45 0.0354 0.0570 A1 - 0.15 - 0.0059 A2 0.90 1.30 0.0354 0.0511 b 0.20 0.50 0.0078 0.0196 C 0.09 0.26 0.0035 0.0102 D 2.70 3.10 0.1062 0.1220 E 2.20 3.20 0.0866 0.1181 E1 1.30 1.80 0.0511 0.0708 A Kingbor Technology TEL:(86)0755-26508846 FAX:(86)0755-26509052 www.kingbor.com e 0.95 REF 0.0374 REF e1 1.90 REF 0.0748 REF L 0.10 0.60 0.0039 0.0236 a 0° 30° 0° 30° 9