EUP2983 White LED Driver For Buck-Boost Application DESCRIPTION FEATURES The EUP2983 is a constant current boost converter specially designed for driving white LEDs with wide input range. The unique converter topology provide a load voltage which can be greater or less than the input voltage. With the tightly regulated load current, the EUP2983 allows series connection with multiple strings of the white LEDs. The brightness of the LEDs can be adjusted through a voltage level on the CTRL pin or by applying a PWM signal to CTRL pin. 1MHz current-mode, pulse-width modulated (PWM) operation allows for small input and output capacitors and a small inductor while minimizing ripple on the input supply/battery. Programmable soft-start eliminates inrush current during startup. The EUP2983 is available in a space-saving, 8-pin 3mm x 3mm TDFN package. z z z z z z z z z 6V to 25V Input Range 32V (typ.) Output with Overvoltage Protection Up to 90% Efficiency Flexible Analog or PWM Dimming Control Internal High Power MOSFET Switch 1MHz PWM Operation Small, Low-Profile Inductors and Capacitors 3mm× 3mm TDFN-8 Package RoHS Compliant and 100% Lead (Pb)-Free APPLICATIONS z z z z 7~10 inch White LED Display Backlighting 12V Automotive Display System PDVD and Subnotebooks LED Lighting Typical Application Circuit Figure 1. High Brightness LEDs Application DS2983 Ver1.2 Nov. 2008 1 EUP2983 Typical Application Circuit Figure 2. WLED Backlight Application Pin Configurations Package Type Pin Configurations TDFN-8 Pin Description PIN TDFN-8 1 PGND 2 IN 3 CTRL 4 FB 5 COMP 6 GND 7 OVP 8 LX DS2983 Ver1.2 DESCRIPTION Power Ground Input Supply Voltage Brightness Control Input. LED brightness is controlled by the voltage applied to CTRL. Varying the voltage from 0.24V to 1.68V adjusts the brightness from dim to bright, respectively. Any voltage above 1.68V does not increase brightness. Current-Sense Feedback Input. Connect a resistor from FB to IN to set the LEDs bias current, The voltage (VFB-VIN) regulates to VCTRL / 10 or 168mV, whichever is lower. Compensation Input. Connect a 0.1µF capacitor (CCOMP) from COMP to GND. CCOMP stabilizes the converter and controls soft-start. CCOMP discharges to GND when in shutdown. Analog Ground. Over voltage Sense. When VOVP is greater than 32V, the internal N-channel MOSFET turns off until VOVP drops below 30V, then the IC re-enters soft-start. Connect a 2.2µF capacitor from OVP to PGND. Inductor Connection. This pin is high impedance during shutdown. Nov. 2008 2 EUP2983 Ordering Information Order Number Package Type Marking Operating Temperature Range EUP2983JIR1 TDFN-8 xxxxx P2983 -40 °C to +85°C EUP2983 □ □ □ □ Lead Free Code 1: Lead Free 0: Lead Packing R: Tape & Reel Operating temperature range I: Industry Standard Package Type J: TDFN Block Diagram Figure 3. DS2983 Ver1.2 Nov. 2008 3 EUP2983 Absolute Maximum Ratings (1) IN to GND -------------------------------------------------------------------------PGND,GND -----------------------------------------------------------------------FB,LX,OVP to GND -------------------------------------------------------------COMP,CTRL to GND ------------------------------------------------------------ILX ------------------------------------------------------------------------------------Package Thermal Resistance TDFN-8,θJA ------------------------------------------------------------------------Junction Temperature ---------------------------------------------------------------Lead Temperature (Soldering, 10sec.) --------------------------------------------Storage Temperature Range -------------------------------------------------------- -0.3V to 31V -0.3V to 0.3V -0.3V to 34V -0.3V to 6V 2A 50°C/W 150°C 260°C -65°C to +150°C Recommend Operating Conditions (2) Supply Voltage , VIN------------------------------------------------------------------ 6V to 25V Operation Temperature Range ------------------------------------------------------ -40°C to +85°C Note (1): Stress beyond those listed under “Absolute Maximum Ratings” may damage the device. Note (2): The device is not guaranteed to function outside the recommended operating conditions. Electrical Characteristics (VIN =8.4V, L1=22uH, CIN=10µF, COUT=2.2µF, CCOMP=0.1µF, R1=7.5, VCTRL=1V, TA=-40°C to +85°C. Refer to Figure 2. Unless otherwise noted. Typical values are at TA= +25°C) Parameter Conditions Supply Voltage UVLO Threshold Quiescent Current OVLO Threshold OVP Input Bias Current Rising Falling Continuous Switching Shutdown VCTRL=0 Rising Falling VOVP=30V, VCTRL>0.24V VOVP=VIN, VCTRL=GND EUP2983 Min Typ Max. 6 4.8 4.5 20 5 4.7 1.2 120 32 30 40 25 5.2 4.9 1.8 200 Unit 60 1 V V V mA uA V V µA µA Error Amplifier CTRL to FB Regulation VCTRL=1V, VIN=8.4V, Temp=25℃ 90 100 110 mV CTRL Input Resistance VCTRL≤1V 200 500 800 KΩ CTRL Dual-Mode Threshold Rising and Falling 100 180 240 mV CTRL Shutdown Enable Delay FB-to-COMP Transconductance VCOMP=1V 8.2 ms 52 µs Oscillator Operating Frequency Maximum Duty Cycle VCTRL=3V,VFB=VIN 0.75 1.0 1.25 MHz 90 92 95 % 0.5 1 Ω 1.4 2 A N-Channel Switch LX On-Resistance LX Current Limit DS2983 Ver1.2 Nov. 2008 Duty Cycle=90% 4 0.8 EUP2983 Typical Operating Characteristics VIN=8.4V Driving Multiple Strings LED 94 92 93 90 91 88 89 Efficiency(%) 86 Efficiency(%) Driving 9 Strings of 3 LEDs 95 84 82 80 78 87 85 83 81 76 VIN=6V 15LEDs 79 74 VIN=8.4V 27LEDs 77 VIN=15V 3LEDs 75 72 70 0 5 10 LED Current(mA) 15 0 20 5 10 LED Current(mA) 15 Soft-Start and Shutdown LED Current vs. Direct-PWM Dimming (FCTRL=1KHz) 22 20 LED Current(mA) 18 16 14 12 10 8 6 4 2 0 0 10 20 30 40 50 60 Duty Cycle(%) 70 80 90 100 VIN=8.4V Driving 5 Strings of 3 LEDs VIN=8.4V Driving 1 String of 3 LEDs DS2983 Ver1.2 Nov. 2008 5 20 EUP2983 Typical Operating Characteristics (continued) VIN=8.4V Driving 9 Strings of 3 LEDs VIN=8.4V CTRL Step Response Direct-PWM Dimming Waveform (FCTRL=1KHz) DS2983 Ver1.2 Nov. 2008 Direct-PWM Dimming Waveform (FCTRL=100KHz) 6 EUP2983 Application Information PWM Dimming Control Soft-Start CTRL is also used as a digital input allowing LED brightness control with a logic-level PWM signal applied directly to CTRL. The frequency range is from 200Hz to 200kHz, while 0% duty cycle corresponds to zero current and 100% duty cycle corresponds to full current. The error amplifier and compensation capacitor form a lowpass filter so PWM dimming results in DC current to the LEDs without the need for any additional RC filters; see the Typical Operating Characteristics. The EUP2983 attains soft-start by charging CCOMP gradually with a current source. When VCOMP rises above 1.25V, the internal MOSFET begins switching at a incremental duty cycle. When VCOMP rises above 2.25V, the duty cycle is at its maximum. See the Typical Operating Characteristics for an example of soft-start operation. Shutdown The EUP2983 enters shutdown when VCTRL is less than 100mV for more than 8.2ms. In shutdown, supply current is reduced to 150µA by powering down the entire IC except for the CTRL voltage-detection circuitry and internal regulator. CCOMP is discharged during shutdown, allowing the device to reinitiate soft-start when it is enabled. Typical shutdown timing characteristics are shown in the Typical Operating Characteristics. Overvoltage Protection Overvoltage lockout (OVLO) occurs when VOUT is above 32V.The protection circuitry stops the internal MOSFET from switching and causes VCOMP to decay to 0V. The device comes out of OVLO and into soft-start when VOUT falls below 30V. In normal operation, EUP2983 VOUT calculates as follows: VOUT = VIN + VFB + VLED × K Adjusting LED Current Adjusting the EUP2983’s output current changes the brightness of the LEDs. An analog input CTRL and the sense-resistor value set the output current. Output current is given by: VCTRL I LED = 10 × R SENSE The VCTRL voltage range for adjusting output current is 0.24V to 1.68V. To set the maximum current, calculate RSENSE when VCTRL is at its maximum as follows: 1.68 10 × I LED(MAX ) Power dissipation in RSENSE is typically less than 10mW, making a standard chip resistor sufficient. DS2983 Ver1.2 Nov. 2008 Inductor Selection Inductor values range from 10µH to 47µH. A 22µH inductor optimizes the efficiency for most applications while maintaining low 50mVP-P input ripple. To prevent core saturation, ensure that the inductor-saturation current rating exceeds the peak inductor current for the application. Calculate the peak inductor current with the following formula: I PEAK = Where K----------number of LEDs in each string VIN--------input voltage VFB--------feedback voltage VLED-------a LED forward voltage R SENSE = Capacitor Selection The exact values of input and output capacitors are not critical. The typical value for the input capacitor is 10µF and the typical value for the output capacitor is 2.2µF. Larger value capacitors can be used to reduce input and output ripple, but at the expense of size and higher cost. CCOMP stabilizes the converter and controls soft-start. Connect a 0.1µF capacitor from COMP to GND. 7 VOUT (MAX ) × I LED(MAX ) VIN (MIN ) × 0.9µs + 0.9 × VIN (MIN ) 2× L Schottky Diode Selection The EUP2983’s high switching frequency demands a high-speed rectification diode (D1) for optimum efficiency. A Schottky diode is recommended due to its fast recovery time and low forward-voltage drop. Ensure that the diode’s average and peak current rating exceed the average output current and peak inductor current. In addition, the diode’s reverse breakdown voltage must exceed VOUT. The RMS diode current can be calculated from: I DIODE (RMS ) = I OUT × I PEAK PC Board Layout Due to fast switching waveforms and high-current paths, careful PC board layout is required. An evaluation kit is available to speed design. When laying out a board, minimize trace lengths between the IC and RSENSE, the inductor, the diode, the input capacitor, and the output capacitor. Keep traces short, direct, and wide. Keep noisy traces, such as the LX node trace, away from FB. The IN bypass capacitor (CIN) should be placed as close to the IC as possible. PGND and GND should be connected directly to the exposed paddle underneath the IC. The ground connections of CIN and COUT should be as close together as possible. The traces from IN to the inductor and from the Schottky diode to the LEDs may be longer. EUP2983 Packaging Information TDFN-8 DETAIL A SYMBOLS A A1 b D D1 E E1 e L DS2983 Ver1.2 Nov. 2008 MILLIMETERS MIN. MAX. 0.70 0.80 0.00 0.05 0.20 0.40 2.90 3.10 2.30 2.90 3.10 1.50 0.65 0.25 0.45 8 INCHES MIN. 0.028 0.000 0.008 0.114 MAX. 0.031 0.002 0.016 0.122 0.090 0.114 0.122 0.059 0.026 0.010 0.018