LM3519 LM3519 High Frequency Boost White LED Driver with High-Speed PWM Brightness Control Literature Number: SNVS394A LM3519 High Frequency Boost White LED Driver with High-Speed PWM Brightness Control General Description Features The LM3519 drives up to 4 white LEDs with constant current to provide LCD backlighting in handheld devices. The LED current is internally set to 20mA. The series connection allows the LED current to be identical for uniform brightness and minimizes the number of traces to the LEDs. Brightness control is achieved by applying a PWM signal on enable with frequencies up to 30kHz. n n n n n The LM3519 features a proprietary PFM regulation architecture with switching frequencies between 2MHz to 8MHz, minimizing inductor size. Over-voltage protection circuitry and high frequency operation permit the use of low-cost small output capacitors. During shutdown, the output is disconnected from the input in order to avoid leakage current path through the LEDs to ground. The LM3519 is available in a tiny 6-pin SOT23 package. n n n n Drives 2 to 4 LEDs at 20mA Up to 30kHz PWM Dimming Control Capability > 80% Peak Efficiency Up to 8MHz Switching Frequency Small External Components: 1H - 3.3H(typ.2.2H) Inductor and 1F Output Capacitor True Shutdown Isolation Over-Voltage Protection Wide Input Voltage Range: 2.7V to 5.5V Small Footprint SOT23-6 Package Applications n LCD, White LED Backlighting on Mobile Phones n Digital Still Cameras and PDAs n General Purpose LED Lighting in Handheld Devices Typical Application 20160201 FIGURE 1. Typical Application Circuit (c) 2005 National Semiconductor Corporation DS201602 www.national.com LM3519 High Frequency Boost White LED Driver with High-Speed PWM Brightness Control September 2005 LM3519 Connection Diagram 6-Lead SOT23 Package 20160202 Top View Pin Descriptions Pin # Name 1 En Description Device Enable Connection 2 Gnd Ground Connection 3 VOUT Output Voltage Connection 4 LED_rtn White LED Current Sensing Input Connection 5 SW Drain Connection of the Internal Power Field Effect Transistor (FET) Switch 6 VIN Input or Supply Voltage Connection Ordering Information Current Option 20 mA www.national.com Order Number Package Marking Supplied As LM3519MK-20 D52B 1000 Units, Tape-and-Reel LM3519MKX-20 D52B 3000 Units, Tape-and-Reel 2 ESD Rating (Note 2) Human Body Model: Machine Model: If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN , En, & LED_rtn Pin -0.3V to +6.5V VOUT , Sw Pin -0.3V to +21V Maximum Junction Temperature (TJ-MAX) Storage Temperature Range 2kV 200V Operating Ratings +150C Junction Temperature (TJ) Range -40C to +125C Ambient Temperature (TA) Range -40C to +85C Input Voltage Range -65C to +150C 2.7V to 5.5V Thermal Properties (Note 4) Junction-to-Ambient Thermal Resistance (JA) 220C/W Electrical Characteristics (Note 5) Limits in standard typeface are for TJ = +25C. Limits in bold typeface apply over the full operating junction temperature range (-40C TJ +125C). VIN = 3.6V, unless otherwise stated. Symbol IQ Parameter Supply Current Conditions Min Typ Max Shutdown: VEN = 0V 0.1 Not Switching: VEN = 1.8V 360 500 Switching: VEN = 1.8V, LED_rtn current = 30mA 550 900 Units A ILED(TOL) LED Current Tolerance/Variation VIN = 3.6V, 2.2H, 4LEDs -10 5.5 10 % OVP Over-Voltage Protection Threshold OVP ON OVP OFF 18 17.8 18.9 18.6 20 19.8 V ILIM Switch Current Limit L = 2.2H RDS(ON) Power NMOS Switch ON Resistance ILEAKAGE Switch Leakage RLED_rtn(ON) LED_rtn NMOS Switch ON Resistance FS Switching Frequency IEN En VSW = 3.6V, VEN = 0V 750 mA 455 m 0.1 2 A 8.0 ILED = 20 mA , L = 1H 4LEDs 5.4 MHz Enable Pin Bias Current (Note 3) VEN = 0V VEN = 1.8V 0.1 1.1 Enable Threshold Device On Device Off A 2 0.9 0.3 V Note 1: Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics table. Note 2: The human body model is a 100pF capacitor discharged through a 1.5k resistor into each pin. The machine model is a 200pF capacitor discharged directly into each pin. Note 3: Current flows into the pin. Note 4: The maximum allowable power dissipation is a function of the maximum junction temperature, TJ(MAX), the junction-to-ambient thermal resistance, JA, and the ambient temperature, TA. See Thermal Properties for the thermal resistance. The maximum allowable power dissipation at any ambient temperature is calculated using: PD(MAX) = (TJ(MAX) - TA)/JA. Exceeding the maximum allowable power dissipation will cause excessive die temperature. Note 5: Min and max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the most likely norm. 3 www.national.com LM3519 Absolute Maximum Ratings (Note 1) LM3519 Block Diagram 20160203 FIGURE 2. Block Diagram www.national.com 4 The LM3519 is a step-up converter for white LED applications that uses a unique and proprietary pulse frequency modulation (PFM) architecture to optimize high efficiency at high frequency operation. Unlike most PFM architecture implementations, the LM3519's unique architectural implementation results in non-pulse skipping variable frequency operation. The regulator is forced to operate at the edge of Continous Conduction Mode (CCM). The error amplifier will set the end of the on-time (IPEAK of inductor) based on the load (LEDs) current. During this operation, the inductor current ramps up and reaches a peak current at end of the on-time. At this point, the internal power switch is turned off until the inductor current reaches zero, and the cycle repeats again. The switching frequency is set based on the charge (on-time) and discharge(off-time) of the inductor current. The frequency can range between 2MHz to 8MHz over the operating input range. The LM3519 operation can be best understood through an examination of the block diagram in Figure 2. When LED During steady-state operation for a typical switching cycle, the oscillator sets the driver logic and turns on N1 power device. N1 conducts current through the inductor and reverse biases the external diode. The LED current is supplied by the output capacitor when N1 is conducting. Once N1 on-time period is concluded, the internal power device is turned off and the external diode is forward baised. The inductor current then flows through the diode to the LED load to replenish the output capacitor and keep the LED current regulated at the trimmed target. 5 www.national.com LM3519 current is out of regulation, the LED_rtn voltage falls below or rises above the internal reference voltage (VREF). The error amplifier will output a signal to increase or decrease the proper on-time duration of N1 power FET. This correction allows the inductor's stored energy to increase or decrease to a sufficient level that when transferred to the load will bring the LED_rtn current back into regulation. Circuit Description LM3519 Typical Performance Characteristics (See Typical Application Circuit : VIN = 3.6V, CIN = 4.7F and COUT = 1F, L = 2.2H and 4 LEDs. TA = +25C, unless otherwise stated.) Efficiency vs VIN Efficiency vs VIN 20160251 20160231 Efficiency vs VIN Efficiency vs VIN 20160233 20160232 IOUT_ACCURACY vs VIN IOUT_ACCURACY vs VIN 20160249 www.national.com 20160250 6 IOUT vs VIN IOUT vs VIN 20160234 20160235 IOUT vs PWM Duty Cycle (VIN = 3.6V, L = 2.2H) IOUT vs VIN 20160260 20160253 IOUT vs PWM Duty Cycle (VIN = 3.6V, L = 1H) IOUT vs PWM Duty Cycle (VIN= 3.6V, L = 2.2H) 20160261 20160259 7 www.national.com LM3519 Typical Performance Characteristics (See Typical Application Circuit : VIN = 3.6V, CIN = 4.7F and COUT = 1F, L = 2.2H and 4 LEDs. TA = +25C, unless otherwise stated.) (Continued) LM3519 Typical Performance Characteristics (See Typical Application Circuit : VIN = 3.6V, CIN = 4.7F and COUT = 1F, L = 2.2H and 4 LEDs. TA = +25C, unless otherwise stated.) (Continued) IOUT vs PWM Duty Cycle (VIN = 3.6V, L = 1H) Switching Frequency vs VIN 20160244 20160207 Switching Frequency vs VIN Switching Frequency vs VIN 20160245 20160209 Switching Frequency vs VIN Peak Inductor Current vs VIN 20160246 www.national.com 20160204 8 Peak Inductor Current vs VIN Peak Inductor Current vs VIN 20160206 20160208 Current Limit vs VIN (4LEDs, 1H) Current Limit vs VIN 20160247 20160248 Iq (non switching) vs Temperature Iq (switching) vs Temperature 20160255 20160256 9 www.national.com LM3519 Typical Performance Characteristics (See Typical Application Circuit : VIN = 3.6V, CIN = 4.7F and COUT = 1F, L = 2.2H and 4 LEDs. TA = +25C, unless otherwise stated.) (Continued) LM3519 Typical Performance Characteristics (See Typical Application Circuit : VIN = 3.6V, CIN = 4.7F and COUT = 1F, L = 2.2H and 4 LEDs. TA = +25C, unless otherwise stated.) (Continued) LED Switch RDS_ON vs Temperature Power Switch RDS_ON vs Temperature 20160258 20160257 Start-up, (VIN = 3.6V, 4LEDs, 2.2H) Start-up (VIN = 3.6V, 4LEDs, 3.3H) 20160219 20160210 Start-up (VIN = 3.6V, 2LEDs, 3.3H) Start-up, (VIN = 3.6V, 2LEDs, 2.2H) 20160220 www.national.com 20160211 10 Typical Switching Waveform (VIN = 3.6V, 4LEDs, 3.3H) Typical Switching Waveform (VIN = 3.6V, 4LEDs, 2.2H) 20160218 20160212 Typical Switching Waveform (VIN = 3.6V, 2LEDs, 2.2H) Typical Switching Waveform (VIN = 3.6V, 3LEDs, 2.2H) 20160214 20160215 Typical Switching Waveform (VIN = 3.6V, 4LEDs, 1H) Typical Switching Waveform (VIN = 3.6V, 3LEDs, 1H) 20160228 20160229 11 www.national.com LM3519 Typical Performance Characteristics (See Typical Application Circuit : VIN = 3.6V, CIN = 4.7F and COUT = 1F, L = 2.2H and 4 LEDs. TA = +25C, unless otherwise stated.) (Continued) LM3519 Application Information CAPACITOR SELECTION To minimize output and input voltage ripple, low equivalent series resistance (ESR) ceramic capacitors are the best choice to use for the input and output filters. For most display applications, a 4.7F capacitor is recommended for CIN and 1F for COUT . AVX TDK Taiyo Yuden muRata Description NR3015T2R2M 2.2H NR3015T3R3M 3.3H 0603 06036D475MAT-6.3V 0603 C2012X5R1A475M-10V 0805 Maufacturer 0805 Vishay TMK212BJ105KG-J EM212BJ475MG-16V 0805 GRM40-034B105K25 0805 GRM39X5R475K6.3 2.1A 3.0x3.0x1.5 mm 1.48A 1.21A Diodes with low forward voltage ratings (VF) and low junction capacitance magnitudes (CJ or CT or CD) are conducive to high efficiency. The chosen diode must have a reverse breakdown voltage rating (VR and/or VRRM) that is larger than the output voltage. The following criteria should be followed when choosing a diode: 1. VR (Diode Blocking Voltage Range) and VRRM (Diode Peak Repetitive Reverse Voltage Rating) > VOUT (Output Voltage) 2. IF or IO (Diode Average Forward Current Rating) ILOAD (Load Current) 3. IFRM (Diode Peak Repetitive Forward Current Rating) ILpeak (Peak Inductor Current) Some recommended diode manufacturers include but are not limited to: Case Size 06033D105MAT-25V 1H DIODE SELECTION Larger output capacitors can be used to reduce ripple voltage. To guarantee good performance, a minimum of 0.47F COUT is required to trade off for large ripple voltage. Care must be taken to account for the true capacitance of a multilayer ceramic capacitor. Smaller case size capacitors typically have less capacitance for a given bias voltage as compared to a larger case size capacitor with the same bias voltage. Please confirm with capacitor manufacturer data before selecting the capacitor. Some recommended capacitor manufacturers include but are not limited to: Manufacturer Taiyo Yuden: NR3015T1R0N Description SS12(1A/20V) SS14(1A/40V) SS16(1A/60V) Central Semiconductor 0603 ONSemi CMSH1- 40M(1A/40V) MBRS1540T3(1.5A/40V) INDUCTOR SELECTION PWM DIMMING In order to maintain sufficient inductance, the saturation current rating of the inductor used with the LM3519 should be higher than the peak inductor current in the target application. Inductors with low DCR values have less power loss and higher efficiency. Larger inductor values such as 2.2H and 3.3H can be used to optimize efficiency, frequency and peak current. If 1H is used, the peak inductor current, frequency will be higher and the efficiency will be lower. Note that the switching frequency ranges will be higher at lower inductance. Typical frequency range is between 4 to 8MHz for 1H, 2 to 5MHz for 2.2H and 2 to 4MHz for 3.3H over the input range. Below is a sample list of low profile inductors. Some recommended inductor manufacturers include but are not limited to: Manufacturer L CoilCraft: DO3314-102 1H DO3314-222 2.2H DO3314-332 3.3H Coilcraft: LPO3310-102ML 1H LPO3310-222ML 2.2H LPO3310-332ML 3.3H Cooper: SD31121R0 1H SD3114-2R2 2.2H SD3114-3R3 3.3uH www.national.com Case Size The LED current is set internally by the LM3519 to 20mA (typical); dimming control may be realized by applying a pulse width modulated(PWM) signal to the En pin. For example, a 50% duty cycle waveform will produce an average current of 10mA. A control signal frequency between 17kHz and 30kHz is suitable for dimming. Although the LM3519 is capable of operation outside this frequency range, it is not recommended to operate below 17kHz for the following reasons: 1) frequency below 100Hz is likely to cause visible flicker in the light emitted by the LED string. 2) frequency below 17kHz may induce audible noise due to combinations of some capacitance/PCB. A PWM frequency above 30kHz is possible but the current linearity vs duty cycle will be affected. If it is not possible to operate the dimming control above 17kHz, audible noise emission may be minimized by using capacitors with low susceptibility to piezoelectric induced stresses, such as poly film designs. Minimum audible noise is most likely to occur when the PWM frequency is less than 2kHz. It is recommended that any application using a PWM control signal below 17kHz be thoroughly evaluated for undesirable audible or visible noise. ISAT 2.1A 3.3x3.3x1.4mm 1.6A 1.4A 1.6A 3.3x3.3x1.0 mm 1.1A DRIVING 2 LEDs The LM3519 is optimized to drive up to 4LEDs. When driving 2LEDs, a minimum inductance of 2.2H is required to maintain good loop regulation and current accuracy. If a smaller inductor is used, the LED current will have more variation with input voltage than a typical application. The following curve illustrates the behavior. 0.95A 2.07A 3.1x3.1x1.4 mm 1.48A 1.15A 12 (Continued) LAYOUT GUIDELINES The input capacitor, CIN, must be placed close to the LM3519. Placing CIN close to the device will reduce the metal trace resistance effect on input voltage ripple. Metal trace connections for the COUT capacitor can increase the effective series resistance, which affects output voltage ripple and efficiency. Trace connections to the inductor should be short and wide to reduce power dissipation, increase overall efficiency and reduce EMI radiation. The diode, like the inductor, should have trace connections that are short and wide to reduce power dissipation and increase overall efficiency. For more details regarding layout guidelines for switching regulators, refer to Applications Note AN1149. IOUT vs VIN 20160239 13 www.national.com LM3519 Application Information LM3519 High Frequency Boost White LED Driver with High-Speed PWM Brightness Control Physical Dimensions inches (millimeters) unless otherwise noted 6-Lead SOT23-6 Package NS Package Number MK06A National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. For the most current product information visit us at www.national.com. LIFE SUPPORT POLICY NATIONAL'S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT AND GENERAL COUNSEL OF NATIONAL SEMICONDUCTOR CORPORATION. As used herein: 1. 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