NJU6048

NJU6048 PRELIMINARY High Efficiency White LED Driver ! GENERAL DESCRIPTION The NJU6048 is a high-efficiency white LED driver. It contains a high-efficiency step-up DC/DC converter and an output driver. The IC can output max.18V and drive as many as 4 white LEDs in series with a constant current, which guarantees the LEDs with uniform brightness. The high frequency of the step-up converter permits the use of small, low-profile inductors and capacitors to minimize the footprint in space-conscious applications. The NJU6048 also features low operating voltage of 1.7V and the small package SOT-23 (MTP-5). All of these benefits make the NJU6048 suitable for the battery-powered portable applications such as cellular phones, camcorders, PDAs, etc. ! PACKAGE OUTLINE NJU6048F ! FEATURES # Drives Up to 4White LEDs in Series IOUT = 20mA(typical) # Uses Small Inductor and Capacitors # 1.7V to 6.5V Operating Voltage for Step-up Circuits (VDD) # Low Switch RDS (ON) VSW = 18V, RDS=0.8Ω (ISW=150mA) # OVP Function # CMOS Technology # Package : SOT-23 5 pin (MTP-5) ! PIN CONFIGURATION (TOP VIEW) SW VSS FB 1 2 3 5 VDD 4 OVP Ver.2005-06-09 -1- NJU6048 ! PIN DESCRIPTIONS No. 1 2 3 4 5 SYMBOL SW VSS FB OVP VDD TYPE Input Power Input Input Power Switch Terminal Ground Terminal Feedback Terminal Over Voltage protection Terminal Power Supply terminal DESCRIPTION ! BLOCK DIAGRAM L1 VI N C1 OVP Bias DC/DC Control + VREF = 0.25V VSS FB FB VDD SW D1 OVP C2 VOUT RLED ILED -2- Ver.2005-06-09 NJU6048 ! FUNCTIONAL DESCRIPTONS (1) LED Current Control and Resistor RLED Selection The NJU6048 incorporates the LED current control to regulate the LED current (ILED), which is programmed by the feedback resistor (RLED) connected between the FB and the VSS terminals. Typically, the reference voltage VREF is internally regulated to 0.25V and is used as the positive input of the built-in comparator. Formula (1) is used to choose the value of the RLED, as shown below. RLED = VREF I LED --- Formula (1) VREF=0.25 (typical) The ILED is the constant current programmed by the RLED. When the feedback voltage on the FB terminal reaches above the reference voltage VREF (i.e., ILED is above the level programmed by RLED), the output capacitor C2 delivers the ILED. Once the feedback voltage drops below the reference voltage (i.e., ILED drops below the level programmed by the RLED), the MOS switch is turned on, then the current of the inductor L1 begins increasing. When the switch current reaches 250mA, the MOS switch is turned off, then the L1 delivers current to the output through the diode D1 as the inductor current drops. After that, the MOS switch is turned on again and the switch current increases up to 250mA. This switching cycle continues until the ILED reaches the level programmed by the RLED, then the ILED current is maintained constant. (2) Over Voltage Protection OVP is designed to prevent the damage of internal NMOS switch in case the increased impedance of the LED load (including the LED opened). Once the device detects over voltage at the output, the internal NMOS switch is kept off until the output voltage drops below 14V. (3) Inductor Selection A 10uH inductor is recommended for most application. The selected inductor must have a saturation current that meets the maximum peak current of the converter. Another important inductor parameter is the DC resistance. The lower DC resistance the device has higher efficiency. (4) Diode Selection A Schottky diode with a low forward-voltage-drop and a fast switching-speed is ideal for the D1. And the D1 must have a rating greater than the output voltage and output current in the system. (5) Capacitor Selection A low ESR (Equivalent Series Resistance) capacitor should be used as the output capacitor C2 to minimize output ripples. A multi-layer ceramic capacitor is the best selection for the NJU6048 application because of not only the low ESR but also small package. Application requires good line regulation ±1%(typ) should use output capacitor larger than 1uF. A ceramic capacitor is also recommended for the input decoupling-capacitor C1, and should be placed as close to the NJU6048 as possible. A 4.7uF is sufficient for most applications. Ver.2005-06-09 -3- NJU6048 ! ABSOLUTE MAXIMUMN RATINGS Ta=25°C PARAMETERS VDD Power Supply OVP Terminal to GND SW Terminal Voltage FB Terminal Voltage Power Dissipation Operating Temperature Storage Temperature Note1) Note2) SYMBOL VDD VOVP VSW VFB PD Topr Tstg CONDITIONS RATINGS -0.3 to +7.0 -0.3 to 18.0V -0.3 to +18.0 -0.3 to VDD 200 -40 to +85 -65 to +150 UNIT V V V mW °C °C SW terminal FB terminal MTP-5 All voltages are relative to VSS = 0V reference. Do not exceed the absolute maximum ratings, otherwise the stress may cause a permanent damage to the IC. It is also recommended that the IC be used in the range specified in the DC electrical characteristics, or the electrical stress may cause mulfunctions and impact on the reliability. ! DC ELECTRICAL CHARACTERISTICS (VDD=3.6V, VSS=0V, Ta=25°C) PARAMETERS VDD Power Supply OVP Threshold OVP Pin Input Current Quiescent Current FB Comparator Trip point Switch Off Time Switch RDS(ON) Switch Current Limit Switch Leakage Current SYMBOL VDD VOVPTH IOVPIC ISTBY1 VFBP tOFF RDS ICL IL Trigger Release VOVP=16V VFB=0.3V VFB =0V ISW=150mA 200 Switch Off, VSW=18V CONDITIONS MIN. 1.7 15 TYP. 16 10 242 250 400 0.8 250 0.1 1.2 300 5.0 MAX. 6.5 17 14 15 80 258 Unit V V V µA µA mV ns Ω mA µA -4- Ver.2005-06-09 NJU6048 • TEST CIRCUITS OVP Threshold Voltage VIN VDD SW OVP A NJU6048 FB 4.7uF VSS V A GND Quiescent Current 15Ω VIN A VDD SW OVP 5V NJU6048 FB 4.7uF VSS 0.3V GND Ver.2005-06-09 -5- NJU6048 FB Comparator Trip point In stepping down VFB from 300mV, VFBP is the threshold voltage to begin switching operation. VIN VDD SW OVP A NJU6048 FB 4.7uF VSS V VFB=300mV →200mV GND Switch Off Time 10uH VIN VDD SW OVP NJU6048 FB 4.7uF VSS 12Ω 1uF GND -6- Ver.2005-06-09 NJU6048 Switch Current Limit / Switch RDS(ON) V VIN VDD SW OVP A NJU6048 FB 4.7uF VSS GND Switch Leakage Current 18V A VIN VDD SW OVP NJU6048 FB 4.7uF VSS GND Ver.2005-06-09 -7- NJU6048 ! TYPICAL PERFORMANCE (VDD=3.6V, VSS=0V, L=10µH, Ta=25°C) Efficiency vs. Output Current Efficiency vs. Input Voltage SW RDS_on vs. Input Voltage SW RDS_on vs. Temperature Current Limit vs. Input Voltage Current Limit vs. Temperature -8- Ver.2005-06-09 NJU6048 (VDD=3.6V, VSS=0V, L=10µH, Ta=25°C) OVP Trigger Threshold vs. Input Voltage OVP Trigger Threshold vs. Temperature OVP Release Threshold vs. Input Voltage OVP Release Threshold vs. Temperature LED Current vs. Input Voltage LED Current vs. Duty Cycle Ver.2005-06-09 -9- NJU6048 (VDD=3.6V, VSS=0V, L=10µH, Ta=25°C) PWM Dimming OVP Waveform Inrush Current Waveform - 10 - Ver.2005-06-09 NJU6048 ! TYPICAL APPLICATION CIRCUITS (1) 4 white LEDs L1 VIN C1 VDD SW OVP C2 D1 VOUT VSS FB RLED1 Referential List of External Components Component LED Driver IC Inductor Schottky Diode Ceramic Capacitor Ceramic Capacitor Chip Resistor White LED Supplier / Parts Number NJRC / NJU6048 Murata / LQH32CN100K23 On Semiconductor / MBR0530 Murata / GRM21BF11A475Z Taiyo Yuden / TMK325BJ105MD Standard Nichia / NSCW215T Qty 1 1 1 1 1 1 4 Value 10uH 4.7uF/10V 1uF/25V 12Ω - IC1 L1 D1 C1 C2 RLED1 LED1 to 4 Ver.2005-06-09 - 11 - NJU6048 (2) 4 white LEDs & Dimming control by external PWM signal L1 VIN C1 VDD SW OVP C2 D1 VOUT VSS FB R3 3V(VBIAS) PWM Input R4 R2 RLED2 Referential List of External Components Component LED Driver IC Inductor Schottky Diode Ceramic Capacitor Ceramic Capacitor Chip Resistor Chip Resistor Chip Resistor Chip Resistor White LED Supplier / Parts Number NJRC / NJU6048 Murata / LQH32CN100K23 On Semiconductor / MBR0530 Murata / GRM21BF11A475Z Taiyo Yuden / TMK325BJ105MD Standard Standard Standard Standard Nichia / NSCW215T Qty 1 1 1 1 1 1 1 1 1 4 Value 10uH 4.7uF/10V 1uF/25V 5.1Ω 15KΩ 300KΩ 430KΩ - IC1 L1 D1 C1 C2 RLED2 R2 R3 R4 LED1 to 4 - 12 - Ver.2005-06-09 NJU6048 MEMO [CAUTION] The specifications on this databook are only given for information , without any guarantee as regards either mistakes or omissions. The application circuits in this databook are described only to show representative usages of the product and not intended for the guarantee or permission of any right including the industrial rights. Ver.2005-06-09 - 13 -