LM3509SDX

LM3509 High Efficiency Boost for White LED's and/or OLED Displays with Dual Current Sinks and I2C Compatible Brightness Control March 6, 2008 LM3509 High Efficiency Boost for White LED's and/or OLED Displays with Dual Current Sinks and I2C Compatible Brightness Control General Description The LM3509 current mode boost converter offers two separate outputs. The first output (MAIN) is a constant current sink for driving series white LED’s. The second output (SUB/FB) is configurable as a constant current sink for series white LED bias, or as a feedback pin to set a constant output voltage for powering OLED panels. When configured as a dual output white LED bias supply, the LM3509 adaptively regulates the supply voltage of the LED strings to maximize efficiency and insure the current sinks remain in regulation. The maximum current per output is set via a single external low power resistor. An I2C compatible interface allows for independent adjustment of the LED current in either output from 0 to max current in 32 exponential steps. When configured as a white LED + OLED bias supply the LM3509 can independently and simultaneously drive a string of up to 5 white LED’s and deliver a constant output voltage of up to 21V for OLED panels. Output over-voltage protection shuts down the device if VOUT rises above 21V allowing for the use of small sized low voltage output capacitors. The LM3509 is offered in a small 10-pin thermally- enhanced LLP package and operates over the -40°C to +85°C temperature range. Features ■ Integrated OLED Display Power Supply and LED Driver ■ Drives up to 10 LED’s at 30mA ■ Drives up to 5 LED’s at 20mA and delivers up to 21V at ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 40mA Over 90% Efficient 32 Exponential Dimming Steps 0.15% Accurate Current Matching Between Strings Internal Soft-Start Limits Inrush Current True Shutdown Isolation for LED’s Wide 2.7V to 5.5V Input Voltage Range 21V Over-Voltage Protection 1.27MHz Fixed Frequency Operation Low Profile 10-pin LLP Package (3mm x 3mm x 0.8mm) General Purpose I/O Active Low Hardware Reset Applications ■ Dual Display LCD Backlighting for Portable Applications ■ Large Format LCD Backlighting ■ OLED Panel Power Supply Typical Application Circuits 30004361 © 2008 National Semiconductor Corporation 300043 www.national.com LM3509 30004301 www.national.com 2 LM3509 Connection Diagram Top View 30004302 10-Pin LLP (3mm × 3mm × 0.8mm) Ordering Information Order Number LM3509SD LM3509SDX Package Type 10-Pin LLP 10-Pin LLP NSC Package Drawing SDA010A SDA010A Top Mark L3509 L3509 Supplied As 1000 units, Tape-and-Reel, No-Lead 4500 units, Tape-and-Reel, No Lead Pin Descriptions/Functions Pin 1 2 3 4 5 6 7 8 9 10 DAP Name MAIN SUB/FB SET VIO RESET/GPIO SW OVP IN SDA SCL GND Main Current Sink Input. Secondary Current Sink Input or 1.25V Feedback Connection for Constant Voltage Output. LED Current Setting Connection. Connect a resistor from SET to GND to set the maximum LED current into MAIN or SUB/FB (when in LED mode), where ILED_MAX = 192×1.244V/RSET. Logic Voltage Level Input Active Low Hardware Reset and Programmable General Purpose I/O. Drain Connection for Internal NMOS Switch Over-Voltage Protection Sense Connection. Connect OVP to the positive terminal of the output capacitor. Input Voltage Connection. Connect IN to the input supply, and bypass to GND with a 1µF ceramic capacitor. Serial Data Input/Output Serial Clock Input Ground Function 3 www.national.com LM3509 Absolute Maximum Ratings (Notes 1, 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN VSW, VOVP, VSUB/FB, VMAIN VSCL, VSDA, VRESET\GPIO, VIO , VSET Continuous Power Dissipation Junction Temperature (TJ-MAX) Storage Temperature Range Maximum Lead Temperature (Soldering, 10s)(Note 3) ESD Rating(Note 10) Human Body Model −0.3V to 6V −0.3V to 25V −0.3V to 23V −0.3V to 6V Internally Limited +150ºC -65ºC to +150º C +300°C 2.5kV Operating Ratings VIN VSW, VOVP, VSUB/FB, VMAIN Junction Temperature Range (TJ)(Note 4) Ambient Temperature Range (TA)(Note 5) (Notes 1, 2) 2.7V to 5.5V 0V to 23V 0V to 21V -40ºC to +110ºC -40ºC to +85ºC Thermal Properties Junction to Ambient Thermal Resistance (θJA)(Note 6) 54°C/W ESD Caution Notice National Semiconductor recommends that all integrated circuits be handled with appropriate ESD precautions. Failure to observe proper ESD handling techniques can result in damage to the device. Electrical Characteristics Specifications in standard type face are for TA = 25°C and those in boldface type apply over the Operating Temperature Range of TA = −40°C to +85°C. Unless otherwise specified VIN = 3.6V, VIO = 1.8V, VRESET/GPIO = VIN, VSUB/FB = VMAIN = 0.5V, R = 12.0kΩ, OLED = ‘0’, ENM = ENS = ‘1’, BSUB = BMAIN = Full Scale.(Notes 2, 7) SET Symbol ILED Parameter Output Current Regulation MAIN or SUB/FB Enabled Maximum Current Per Current Sink Conditions UNI = ‘0’, or ‘1’ RSET = 8.0kΩ UNI = ‘1’ (Note 11) 3.0V < VIN < 5V Min 18.6 Typ 20 30 0.15 1.244 192 500 Max 21.8 Units mA 1 % V ILED-MATCH VSET ILED/ISET VREG_CS VREG_OLED VHR RDSON ICL VOVP fSW DMAX DMIN IQ IMAIN to ISUB/FB Current Matching SET Pin Voltage ILED Current to ISET Current Ratio Regulated Current Sink Headroom Voltage mV 1.239 V mV Ω 875 22.9 21.2 1.4 mA V MHz % % 440 µA VSUB/FB Regulation Voltage 3.0V < VIN < 5.5V, OLED = ‘1’ in OLED Mode Current Sink Minimum Headroom Voltage NMOS Switch On Resistance Output Over-Voltage Protection Switching Frequency Maximum Duty Cycle Minimum Duty Cycle Quiescent Current, Device Not Switching VMAIN and VSUB/FB > VREG_CS, BSUB = BMAIN = 0x00 VSUB/FB > VREG_OLED, OLED=’1’, ENM=ENS=’0’ ILED = 95% of nominal ISW = 100mA 1.172 1.21 300 0.58 NMOS Switch Current Limit VIN = 3.0V ON Threshold OFF Threshold 650 21.2 19.7 1.0 770 22 20.6 1.27 90 10 400 250 3.6 305 5 µA ISHDN Shutdown Current ENM = ENS = OLED = '0' www.national.com 4 LM3509 Symbol VIL VIH VOL VIO VIL VIH VOL t1 t2 t3 t4 Parameter Input Logic Low Input Logic High Output Logic Low Serial Bus Voltage Level Input Logic Low Input Logic High Output Logic Low SCL Clock Period Data In Setup Time to SCL High Data Out Stable After SCL Low SDA Low Setup Time to SCL Low (Start) SDA High Hold Time After SCL High (Stop) Conditions 2.7V < VIN 0.3V. OUTPUT CAPACITOR SELECTION The LM3509’s output capacitor supplies the LED current during the boost converters on time. When the switch turns off the inductor energy is discharged through the diode supplying power to the LED’s and restoring charge to the output capacitor. This causes a sag in the output voltage during the on time and a rise in the output voltage during the off time. The output capacitor is therefore chosen to limit the output ripple to an acceptable level depending on LED or OLED panel current requirements and input/output voltage differentials. For proper operation ceramic output capacitors ranging from 1µF to 2.2µF are required. As with the input capacitor, the output voltage ripple is composed of two parts, the ripple due to capacitor discharge (delta VQ) and the ripple due to the capacitors ESR (delta VESR). For continuous conduction mode, the ripple components are found by: In the typical application circuit a 1µF ceramic input capacitor works well. Since the ESR in ceramic capacitors is typically less than 5mΩ and the capacitance value is usually small, the input voltage ripple is primarily due to the capacitive discharge. With larger value capacitors such as tantalum or aluminum electrolytic the ESR can be greater than 0.5Ω. In this case the input ripple will primarily be due to the ESR. Table 7 lists different manufacturers for various capacitors and their case sizes that are suitable for use with the LM3509. When configured as a dual output LED driver a 1µF output capacitor is adequate. In OLED mode for output voltages above 12V a 2.2µF output capacitor is required (see Low Output Voltage Operation (OLED) Section). 19 www.national.com LM3509 TABLE 7. Recommended Output Capacitors Manufacturer TDK Murata TDK Murata Part Number C1608X5R1E105M GRM39X5R105K25D53 9 C2012X5R1E225M GRM219R61E225KA12 Value 1µF 1µF 2.2µF 2.2µF Case Size 0603 0603 0805 0805 Voltage Rating 25V 25V 25V 25V INDUCTOR SELECTION The LM3509 is designed for use with a 10µH inductor, however 22µH are suitable providing the output capacitor is increased 2×'s. When selecting the inductor ensure that the saturation current rating (ISAT) for the chosen inductor is high enough and the inductor is large enough such that at the maximum LED current the peak inductor current is less than the LM3509’s peak switch current limit. This is done by choosing: Values for IPEAK can be found in the plot of peak current limit vs. VIN in the Typical Performance Characteristics graphs. Table 8 shows possible inductors, as well as their corresponding case size and their saturation current ratings. TABLE 8. Recommended Inductors Manufacturer TDK TDK TOKO Part Number VLF3012AT-100M R49 VLF4012AT-100M R79 A997AS-100M Value 10µH 10µH 10µH Dimensions 2.6mm×2.8mm×1 mm 3.5mm×3.7mm×1. 2mm 3.8mm×3.8mm×1. 8mm ISAT 490mA 800mA 580mA DC Resistance 0.36Ω 0.3Ω 0.18Ω DIODE SELECTION The output diode must have a reverse breakdown voltage greater than the maximum output voltage. The diodes average current rating should be high enough to handle the LM3509’s output current. Additionally, the diodes peak current rating must be high enough to handle the peak inductor current. Schottky diodes are recommended due to their lower forward voltage drop (0.3V to 0.5V) compared to (0.6V to 0.8V) for PN junction diodes. If a PN junction diode is used, ensure it is the ultra-fast type (trr < 50ns) to prevent excessive loss in the rectifier. For Schottky diodes the B05030WS (or equivalent) work well for most designs. See Table 9 for a list of other Schottky Diodes with similar performance. TABLE 9. Recommended Schottky Diodes Manufacturer Diodes Inc. Philips ON Semiconductor Part Number B05030WS BAT760 NSR0320MW2T Package SOD-323 SOD-323 SOD-323 Reverse Breakdown Voltage 30V 23V 30V Average Current Rating 0.5A 1A 1A www.national.com 20 LM3509 OUTPUT CURRENT RANGE (OLED MODE) The maximum output current the LM3509 can deliver in OLED mode is limited by 4 factors (assuming continuous conduction); the peak current limit of 770mA (typical), the inductor value, the input voltage, and the output voltage. Calculate the maximum output current (IOUT_MAX) using the following equation: TABLE 10. Component Values for Output Voltage Selection VOUT 18V 15V 12V 9V 7V COUT 2.2µF 2.2µF 4.7µF 10µF 10µF 22µF L 10µH 10µH 10µH 10µH 4.7µH 4.7µH VIN Range 2.7V to 5.5V 2.7V to 5.5V 2.7V to 5.5V 2.7V to 5.5V 2.7V to 5.5V 2.7V to 4.5V For the typical application circuit with VOUT = 18V and assuming 70% efficiency, the maximum output current at VIN = 2.7V will be approximately 70mA. At 4.2V due to the shorter on times and lower average input currents the maximum output current (at 70% efficiency) jumps to approximately 105mA. Figure 11 shows a plot of IOUT_MAX vs. VIN using the above equation, assuming 80% efficiency. In reality factors such as current limit and efficiency will vary over VIN, temperature, and component selection. This can cause the actual IOUT_MAX to be higher or lower. 5V 30004362 FIGURE 11. Typical Maximum Output Current in OLED Mode OUTPUT VOLTAGE RANGE (OLED MODE) The LM3509's output voltage is constrained by 2 factors. On the low end it is limited by the minimum duty cycle of 10% (assuming continuous conduction) and on the high end it is limited by the over voltage protection threshold (VOVP) of 22V (typical). In order to maintain stability when operating at different output voltages the output capacitor and inductor must be changed. Refer to Table 10 for different VOUT, C OUT, and L combinations. LAYOUT CONSIDERATIONS The LLP is a leadless package with very good thermal properties. This package has an exposed DAP (die attach pad) at the underside center of the package measuring 1.6mm x 2.0mm. The main advantage of this exposed DAP is to offer low thermal resistance when soldered to the thermal ground pad on the PCB. For good PCB layout a 1:1 ratio between the package and the PCB thermal land is recommended. To further enhance thermal conductivity, the PCB thermal ground pad may include vias to a 2nd layer ground plane. For more detailed instructions on mounting LLP packages, please refer to National Semiconductor Application Note AN-1187. The high switching frequencies and large peak currents make the PCB layout a critical part of the design. The proceeding steps must be followed to ensure stable operation and proper current source regulation. 1, Divide ground into two planes, one for the return terminals of COUT, CIN and the I2C Bus, the other for the return terminals of RSET and the feedback network. Connect both planes to the exposed PAD, but nowhere else. 2, Connect the inductor and the anode of D1 as close together as possible and place this connection as close as possible to the SW pin. This reduces the inductance and resistance of the switching node which minimizes ringing and excess voltage drops. This will improve efficiency and decrease noise that can get injected into the current sources. 3, Connect the return terminals of the input capacitor and the output capacitor as close as possible to the exposed PAD and through low impedance traces. 4, Bypass IN with at least a 1µF ceramic capacitor. Connect the positive terminal of this capacitor as close as possible to IN. 5, Connect COUT as close as possible to the cathode of D1. This reduces the inductance and resistance of the output bypass node which minimizes ringing and the excess voltage drops. This will improving efficiency and decrease noise that can get injected into the current sources. 6, Route the traces for RSET and the feedback divider away from the SW node to minimize noise injection. 7, Do not connect any external capacitance to the SET pin. 21 www.national.com LM3509 Physical Dimensions inches (millimeters) unless otherwise noted 10 Pin LLP For Ordering, Refer to Ordering Information Table NS Package Number SDA10A X1 = 3mm (±0.1mm), X2 = 3mm (±0.1mm), X3 = 0.8mm www.national.com 22 LM3509 Notes 23 www.national.com LM3509 High Efficiency Boost for White LED's and/or OLED Displays with Dual Current Sinks and I2C Compatible Brightness Control Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: Products Amplifiers Audio Clock Conditioners Data Converters Displays Ethernet Interface LVDS Power Management Switching Regulators LDOs LED Lighting PowerWise Serial Digital Interface (SDI) Temperature Sensors Wireless (PLL/VCO) www.national.com/amplifiers www.national.com/audio www.national.com/timing www.national.com/adc www.national.com/displays www.national.com/ethernet www.national.com/interface www.national.com/lvds www.national.com/power www.national.com/switchers www.national.com/ldo www.national.com/led www.national.com/powerwise www.national.com/sdi www.national.com/tempsensors www.national.com/wireless WEBENCH Analog University App Notes Distributors Green Compliance Packaging Design Support www.national.com/webench www.national.com/AU www.national.com/appnotes www.national.com/contacts www.national.com/quality/green www.national.com/packaging www.national.com/quality www.national.com/refdesigns www.national.com/feedback Quality and Reliability Reference Designs Feedback THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION (“NATIONAL”) PRODUCTS. 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