LM3590 Series White LED Driver General Description Features The LM3590 is a White LED constant current driver capable of supplying up to 3 White LEDs connected in series with 20mA. This device operates over a wide 6V-12.6V input voltage range. The output can accomodate LEDs with a combined forward voltage of up to 11.5V, from a 12V input supply. The LED drive current is programmed by using an external resistor on the ISET pin. n n n n LED brightness can be linearly varied up to the programmed LED current by applying a Pulse Width Modulated (PWM) signal to the EN pin of the device. The LED output current of the LM3590 is tightly controlled over temperature and voltage. LED Current matching is guaranteed due to the series configuration of the LEDs. The series topology also simplifies the connection between the White LEDs in the display module and the LM3590 since only one connection is required. The LM3590 typically draws only 50µA when operating in the no-load condition and draws less than 0.1µA when the device is shut down. n n n n n n Drives up to 3 stacked white LEDs 6.0V-12.6V input voltage range Up to 20mA LED output current Excellent LED current matching guaranteed by series configuration Single connection to the White LEDs in the display module Tightly controlled programmable current source Low shutdown current (0.1µA typ.) PWM brightness control Very small solution size SOT23-5 package: 3mm x 3mm x 1.0mm (LxWxH) Applications n White LED Display Backlights n Keypad Backlights n General purpose constant current driver for high forward-voltage LEDs The LM3590 is available in a small 5-pin SOT23 package. Typical Application Circuit 20081301 20081305 © 2003 National Semiconductor Corporation DS200813 www.national.com LM3590 Series White LED Driver November 2003 LM3590 Connection Diagram 20081302 Ordering Information Order Number Package Description Package Marking Supplied As Tape and Reel LM3590MF SOT23-5 SABB*¢Z¢1¢X 250 Units, Tape and Reel LM3590MFX SOT23-5 SABB*¢Z¢1¢X 3000 Units, Tape and Reel Pin Description Pin # Name 1 ISET Programmable LED current Input. The LED current has the following relationship with the resistor used: 2 GND Ground Connection 3 IOUT Constant Current LED Output 4 VIN Power Supply Voltage Input. Input voltage range: 6V-12.6V 5 EN Device Enable Function RSET = 100 x (125 ÷ IOUT) www.national.com 2 Operating Conditions (Notes 1, 2) Input Voltage Range If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. EN Voltage Range 0V to VIN VIN −0.3 to 13.0V Max Ambient Temperature (TA) Range (Note 4) EN −0.3 to (VIN+0.3V) w/ 13.0V max Junction Temperature (TJ) Range Maximum Junction Temperature (TJMAX) Storge Temperature 150˚C ESD Rating (Note 3) 1.5kV Machine Model 200V −40˚C to +110˚C Junction-to-Ambient Thermal Resistance, SOT23-5 Package (θJA) (Note 5) 260˚C Human Body Model −40˚C to +85˚C Thermal Information −65˚C to +150˚C Maximum Lead Temperature (Soldering, 5 sec.) 6.0V to 12.6V 220˚C/W Electrical Characteristics (Notes 2, 6) Limits in standard typeface are for TJ = 25˚C and limits in boldface type apply over the full Operating Junction Temperature Range (−40˚C ≤ TJ ≤ +110˚C). Unless otherwise specified, CIN = 1 µF, VIN = 12.0V, VEN = 3.0V, RSET = 6.19kΩ, VIOUT = 10.8V. Symbol IOUT Parameter Output Current Capability Min Typ Max VIN = 12V 7.5V ≤ VIOUT ≤ 11.5V Conditions 19 (−5%) 20 21 (+5%) VIOUT = 10.8V 11.3V ≤ VIN ≤ 12.6V 19 (−5%) 20 21 (+5%) RSET = 8.35kΩ 15 RSET = 12.5kΩ 10 Output Current Programming 125 ÷ RSET IOUT ratio to ISET Units mA A 100:1 IQ Quiescent Supply Current 11.3V ≤ VIN ≤ 12.6V RSET = OPEN IOUT = OPEN 50 75 µA ISD Shutdown Supply Current VIN = 12.6V VEN = 0V 0.1 1 µA VISET ISET Reference Voltage VHR Minimum Current Source Voltage Headroom (VIN − VIOUT)(Note 7) VIH Logic Input EN: High level 1.1 VIL Logic Input EN: Low level 0 IEN Enable Pin Input Current(Note 8) tON Turn-On Time IOUT = 95% nominal IOUT = 90% of steady state 1.25 V 300 mV VIN 0.3 V V 6 µA 50 µs 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 performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics table. Note 2: All voltages are with respect to the potential at the GND pin. Note 3: The human-body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 220pF capacitor discharged directly into each pin. Note 4: Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 110oC), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to-ambient thermal resistance of the part/package in the application (θJA), as given by the following equation: TA-MAX = TJ-MAX-OP - (θJA x PD-MAX). The ambient temperature operating rating is provided merely for convenience. This part may be operated outside the listed TA rating, so long as the junction temperature of the device does not exceed the maximum operating rating of 110oC. Note 5: Junction-to-ambient thermal resistance is highly application and board-layout dependent. In applications where high maximum power dissipation exists, special care must be paid to thermal dissipation issues. For more information on these topics, please refer to the Power Dissipation section of this datasheet. 3 www.national.com LM3590 Absolute Maximum Ratings LM3590 Electrical Characteristics (Notes 2, 6) (Continued) Note 6: All room temperature limits are 100% tested or guaranteed through statistical analysis. All limits at temperature extremes are guaranteed by correlation using standard Statistical Quality Control methods (SQC). All limits are used to calculate Average Outgoing Quality Level (AOQL). Typical numbers are not guaranteed, but do represent the most likely norm. Note 7: The current source is connected internally between VIN and VIOUT. The voltage across the current source, [VIN − VIOUT], is referred to as headroom voltage. For the current source to regulate properly, a minimum headroom voltage must be present across it. Minimum required headroom voltage is proportional to the current flowing through the current source, as dictated by this equation: VHR-MIN = 300mV x (IOUT ÷ 20mA). Note 8: An internal 500kΩ pull-down resistor is connected between the EN and GND pins. Functional Block Diagram 20081314 www.national.com 4 IOUT vs VIN IOUT vs VIOUT 20081305 20081304 IOUT vs RSET IQ vs VIN 20081307 20081306 VSET vs VIN Shutdown Supply Current vs VIN 20081308 20081309 5 www.national.com LM3590 Typical Performance Characteristics Unless otherwise specified, CIN = 1µF, VIN = 12.0V, VEN = 3.0V, VIOUT = 10.8V, RSET = 6.19kΩ, TA = 25˚C. CIN is a low ESR multi-layer ceramic capacitor (MLCC). LM3590 Typical Performance Characteristics Unless otherwise specified, CIN = 1µF, VIN = 12.0V, VEN = 3.0V, VIOUT = 10.8V, RSET = 6.19kΩ, TA = 25˚C. CIN is a low ESR multi-layer ceramic capacitor (MLCC). (Continued) Shutdown Threshold vs VIN Startup 20081311 20081310 www.national.com 6 required headroom voltage is proportional to the current flowing through the current source, as dictated by the equation: VHR-MIN = kHR x IOUT CIRCUIT DESCRIPTION The LM3590 is a constant current series White-LED Driver, providing up to 20mA from an input voltage between 7.5V to 12.6V. To set the LED drive current, the LM3590 uses a resistor connected to the ISET pin to set a reference current. This reference current is then multiplied and mirrored to the constant current output, IOUT. The LED brightness can be controlled by applying a PWM (Pulse Width Modulation) signal to the Enable pin (EN). (see PWM BRIGHTNESS CONTROL PROCEDURES section). The parameter kHR, typically 15mV/mA in the LM3590, is a proportionality constant that represents the ON-resistance of the internal current mirror transistors. For worst-case design calculations, using a kHR of 20mV/mA is recommended. (Worst-case recommendation accounts for parameter shifts from part-to-part variation and applies over the full operating temperature range). Figure 1 shows how output current of the LM3590 varies with respect to headroom voltage. ENABLE MODE The Enable pin (EN) disables the part and reduces the quiescent current to 0.1µA (typ.). The LM3590 has an activehigh enable pin (LOW = shut down, HIGH = operating). The LM3590 EN pin can be driven with a low-voltage CMOS logic signal (1.5V logic, 1.8V logic, etc). There is an internal 500kΩ pull-down between the EN and GND pins of the LM3590. CAPACITOR SELECTION Although not required for normal operation, a capacitor can be added to the voltage input of the LM3590 to reduce line noise. A surface-mount multi-layer ceramic capacitor (MLCC) is recommended. MLCCs are small, inexpensive and have very low equivalent series resistance (ESR, ≤15mΩ typ.). MLCCs with a X5R or X7R temperature characteristic are preferred for use with the LM3590. Table 1. Ceramic Capacitor Manufacturers lists suggested capacitor suppliers for the typical application circuit. 20081312 TABLE 1. Ceramic Capacitor Manufacturers Manufacturer Contact TDK www.component.tdk.com Murata www.murata.com Taiyo Yuden www.t-yuden.com FIGURE 1. IOUT vs VHR VHR = VIN − VIOUT VIN = 12.0V On the flat part of the graph, the current is regulated properly as there is sufficient headroom voltage for regulation. On the sloping part of the graph the headroom voltage is too small, the current source is squeezed, and the current drive capability is limited. Thus, operating the LM3590 with insufficient headroom voltage across the current source should be avoided. LED SELECTION The LM3590 is designed to drive up to 3 LEDs with the combined forward voltages of the LEDs being no greater than 11.5V, when using a 12V input supply. The typical and maximum diode forward voltage depends highly on the manufacturer and their technology. Table 2. White LED Selection lists two suggested manufacturers. LED Forward current matching is guaranteed by design, due to the series LED configuration of the LM3590. ISET PIN An external resistor, RSET, connected to the ISET pin sets the output current. The internal current mirror sets the series LED output current with a 100:1 ratio to the current through RSET. The current matching through each LED is guaranteed by the series LED drive topology. The following equation approximates the LED current: IOUT = 100 x (1.25V ÷ RSET) (Amps) TABLE 2. White LED Selection Manufacturer Contact Osram www.osram-os.com Nichia www.nichia.com PWM BRIGHTNESS CONTROL PROCEDURES The brightness of the LEDs can be linearly varied from zero up to the maximum programmed current level by applying a Pulse-Width-Modulated signal to the EN pin of the LM3590. The following procedures illustrate how to program the LED drive current and adjust the output current level using a PWM signal. 1. Determine the maximum desired IOUT current. Use the IOUT equation to calculate RSET LED HEADROOM VOLTAGE (VHR) A single current source is connected internally between VIN and IOUT. The voltage across the current source, (VIN − VIOUT), is referred to as headroom voltage (VHR). The current source requires a sufficient amount of headroom voltage to be present across it in order to regulate properly. Minimum 7 www.national.com LM3590 Application Information LM3590 Application Information 2. the power consumed by the LEDs, TAis the ambient temperature, and θJA is the junction-to-ambient thermal resistance for the SOT23-5 package. VIN is the input voltage to the LM3590, VIOUT is the sum of the forward voltages of LEDs connected to the IOUT pin, and IOUT is the programmed LED current. PDISSIPATION = PIN - PIOUT (Continued) Brightness control can be implemented by pulsing a signal at the EN pin. LED brightness is proportional to the duty cycle (D) of the PWM signal. For linear brightness control over the full duty cycle adjustment range, the PWM frequency (f) should be limited to accommodate the turn-on time (TON = 50µs) of the device. D x (1/f) > TON fMAX = DMIN ÷ TON If the PWM frequency is much less than 100Hz, flicker may be seen in the LEDs. For the LM3590, zero duty cycle will turn off the LEDs and a 50% duty cycle will result in an average IOUT being half of the programmed LED current. For example, if RSET is set to program 15mA, a 50% duty cycle will result in an average ILED of 7.5mA. = (VIN x IOUT) − (VIOUT x IOUT) TJ = TA + (PDISSIPATION x θJA) The junction temperature rating takes precedence over the ambient temperature rating. The LM3590 may be operated outside the ambient temperature rating, so long as the junction temperature of the device does not exceed the maximum operating rating of 110˚C. The maximum ambient temperature rating must be derated in applications where high power dissipation and/or poor thermal resistance causes the junction temperature to exceed 110˚C. POWER DISSIPATION The power dissipation (PDISSIPATION) and junction temperature (TJ) can be approximated with the equations below. PIN is the product of the input current and input voltage, PIOUT is Application Circuits Figure 2 shows how to program the LED current to four different DC levels using two digital logic signals. The programmed LED current is a function of the equivalent resis- tance on the ISET pin (RISET), resulting from the logic signals on SET1 and SET2. Example values for R1, R2, and RSET an the resulting 4 current levels are shown below. 20081313 FIGURE 2. Example: R1 = 15.8kΩ, R2 = 31.6kΩ, RSET = 31.6kΩ TABLE 3. Digital LED Current Programming EN SET1 SET2 0 X X 1 1 1 1 1 0 1 0 1 0 www.national.com RISET Example RISET Example IOUT Shutdown Shutdown Shutdown RSETiR1iR2 31.6kΩi15.kΩi31.6kΩ 16mA RSETiR1 31.6kΩi15.kΩ 12mA 1 RSETiR2 31.6kΩi31.6kΩ 8mA 0 RSET 31.6kΩ 4mA 8 LM3590 Series White LED Driver Physical Dimensions inches (millimeters) unless otherwise noted 5 Lead Small Outline Package (SOT23-5) NS Package Number MF05A 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. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. 2. A critical component is any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. BANNED SUBSTANCE COMPLIANCE National Semiconductor certifies that the products and packing materials meet the provisions of the Customer Products Stewardship Specification (CSP-9-111C2) and the Banned Substances and Materials of Interest Specification (CSP-9-111S2) and contain no ‘‘Banned Substances’’ as defined in CSP-9-111S2. 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