LM3595 Parallel White-LED Driver General Description Features The LM3595 is a parallel white-LED driver that is capable of driving four white LEDs. It can supply a total output current of 100mA over an input voltage range of 3.0V to 5.5V. The amount of constant current sourced to the outputs is user selectable using one external sense resistor. LM3595 typically draws 0.03µA when placed in shutdown, and 200µA when operating in the no-load condition. If any of the outputs are not used, leave the pin(s) unconnected. Brightness can be controlled by both analog and PWM techniques. A voltage between 0V and 3V may be applied to the BRGT pin to vary the current. Output current will linearly track the voltage applied to the BRGT pin. An active-low level must be present on the BR-ON pin for analog brightness control to be disabled. Alternatively, a PWM signal can be applied to the EN pin to vary the perceived brightness of the LED. n Regulated IOUT with ± 0.5% matching between constant current outputs n Drives one, two, three or four white LED’s with no bias resistors n 3.0V to 5.5V Input voltage n Up to 100mA output current n Active-High Enable Pin n Analog Brightness Control n Very small solution size n LLP-10 package: 3.0mm x 3.0mm x 0.8mm n Very Low Shutdown current (0.03µA typ.) The LM3595 uses an active-high enable level. The LM3595 is available in National’s LLP-10 package. Applications n Portable devices using white or blue LEDs with display and backlight or frontlight n Keypad LEDs n Strobe LEDs Typical Application Circuit 20072201 © 2003 National Semiconductor Corporation DS200722 www.national.com LM3595 Parallel White-LED Driver August 2003 LM3595 Connection Diagram LM3595 10-Pin Leadless Leadframe Package (LLP) - 3mm X 3mm NS Package Number LDA10A 20072202 Pin Description Pin Name Description 9 VIN 1,2,3,4 OUT1-4 5 Input Voltage ISET Current Set Input- The resistor value tied between this pin and ground sets the output current. EN Active-High Enable Input - A 1MΩ resistor is connected internally between this pin and GND to pull the voltage on this pin to 0V, and shut down the part, when the pin is left floating. BR-ON Active-High Analog Brightness Control Enable - A voltage of .65 x VIN must be applied to this pin to enable analog brightness control. BRGT Analog-voltage-controlled Brightness Input - When the BR-ON pin is set high, the voltage on this pin allows analog control of the LED’s brightness. The recommended voltage range on this pin is 0 - 3 V where 3V is VBR(MAX). The input impedance of this pin is 300kΩ. GND Ground 6 10 7 8, DAP Current Source Outputs 1- 4 - Connect directly to LED’s Ordering Information Order Number www.national.com Package Number Package Marking Supplied as: LM3595LD LDA10A L3595 1000 units on Tape-and-Reel LM3595LDX LDA10A L3595 3500 units on Tape-and-Reel 2 Operating Ratings (Notes 1, (Notes 1, 2) 2) Input Voltage Range (Note 5) 3.0V to 5.5V If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. Output Voltage Range (Note 5) 2.0V to 5.5V VIN −0.3V to 6.0V EN, BR-ON, BRGT -0.3V to (VIN+ 0.3V) w/ 6.0V max Junction Temperature (TJ-MAX-ABS) Junction Temperature Range (Note 6) Ambient Temperature Range (Note 6) Internally Limited Storage Temperature Range -65˚C to 150˚C Lead Temperature (Soldering, 5 Sec.) -40˚C to 85˚C Thermal Information 150˚C Continuous Power Dissiation (Note 3) -40˚C to 105˚C Junction-to-Ambient Thermal Resistance, LLP-10 Package (θJA) (Note 7) 55˚C/W 260˚C ESD Rating (Note 4) Human-body model Machine model 2 kV 200V Electrical Characteristics (Notes 2, 8) Limits in standard typeface and typical values apply for TJ = 25oC. Limits in boldface type apply over the operating junction temperature range. Unless otherwise specified: VIN = 5V, VOUTX = 3.6V, RSET = 8.25kΩ, V(EN) = VIN, V(BR-ON) = 0V Symbol IOUTX IOUTX-BRGT Parameter Output Current Regulation (Note 5) Analog Brightness Control Current Regulation Min Typ Max 3.0V ≤ VIN ≤ 5.5V 2.0V ≤ VOUTX ≤ (VIN - 0.7V) RSET = 4.99kΩ Conditions 22.54 (-8%) 24.5 26.46 (+8%) 3.0V ≤ VIN ≤ 5.5V 2.0V ≤ VOUTX ≤ (VIN - 0.42V) RSET = 8.25kΩ 13.80 (-8%) 15.0 16.20 (+8%) 3.0V ≤ VIN ≤ 5.5V 2.0V ≤ VOUTX ≤ (VIN - 0.28V) RSET = 12.4kΩ 9.20 (-8%) 10.0 10.80 (+8%) 13.83 (-6.5%) 14.8 15.77 (+6.5%) mA (%) 100 250 µA 0.5 4 % V (%) V(BRGT) = 3.0V, V(BR-ON) = VIN V(BRGT) = 0V, V(BR-ON) = VIN Units mA (%) IOUT-MATCH Current Matching Between Any Two Outputs VSET ISET Pin Voltage 1.147 (-6%) 1.22 1.293 (+6%) IOUTX/ISET Output Current to Current Set Ratio 95 (-5%) 100 105 (+5%) IOUT = 95% x IOUT(nom) RSET = 4.99kΩ (IOUT(nom) approx. 25mA) 500 690 VHR Current Source Headroom Voltage (Note 5) IOUT = 95% x IOUT(nom) RSET = 12.4kΩ (IOUT(nom) approx. 10mA) 200 280 IOUTX = 0mA, V(BR-ON) = VIN, RSET = Open 200 300 µA IOUTX = 0mA, V(BR-ON) = VIN, RSET = 8.25kΩ 350 mV IQ Quiescent Supply Current ISD Shutdown Supply Current EN = 0, V(BR-ON) = VIN 1 µA VEN-IH EN Input Logic High 3.0V ≤ VIN ≤ 5.5V 1.2 VIN V VEN-IL EN Input Logic Low 3.0V ≤ VIN ≤ 5.5V 0 .5 V VBRON-IH BR-ON Input Logic High 3.0V ≤ VIN ≤ 5.5V .65 x VIN VIN V VBRON-IL BR-ON Input Logic Low 3.0V ≤ VIN ≤ 5.5V 0 .35 x VIN V 3 0.03 www.national.com LM3595 Absolute Maximum Ratings LM3595 Electrical Characteristics (Notes 2, 8) (Continued) Limits in standard typeface and typical values apply for TJ = 25oC. Limits in boldface type apply over the operating junction temperature range. Unless otherwise specified: VIN = 5V, VOUTX = 3.6V, RSET = 8.25kΩ, V(EN) = VIN, V(BR-ON) = 0V Symbol Parameter IEN EN Pin Current (Note 9) IBR-ON BR-ON Pin Current Conditions V(EN) = 1.5V Min Typ Max 1.5 V(EN) = 0V 0 0 ≤ VBR-ON ≤ VIN 0 Units µA µA Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component 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 tables. Note 2: All voltages are with respect to the potential at the GND pin. Note 3: Thermal shutdown circuitry protects the device from permanent damage. Note 4: The Human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin. The machine model is a 200pF capacitor discharged directly into each pin. MIL-STD-883 3015.7 Note 5: The operation rating for minimum input voltage, VMIN, is limited by VOUTX and IOUTX as dictated by headroom voltage. The equation, VMIN ≥ (VOUTX+VHR), must be satisfied for the desired output current to be realized. For more information, see the section on Output Current Capability found in this datasheet. Note 6: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = 105˚C), 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). Note 7: Junction-to-ambient thermal resistance (θJA) is taken from a thermal modeling result, performed under the conditions and guidelines set forth in the JEDEC standard JESD51-7. The test board is a 4-layer FR-4 board measuring 102mm x 76mm x 1.6mm with a 2x1 array of thermal vias. The ground plane on the board is 50mm x 50mm. Thickness of copper layers are 36µm/18µm/18µm/36µm (1.5oz/1oz/1oz/1.5oz). Ambient temperature in simulation is 22˚C, still air. Power dissipation is 1W. The value of θJA of the LM3595 in LLP-10 could fall in a range as wide as 50˚C/W to 150˚C/W (if not wider), depending on PWB material, layout, and environmental conditions. In applications where high maximum power dissipation exists (high VIN, high IOUT), special care must be paid to thermal dissipation issues. For more information on these topics, please refer to Application Note 1187: Leadless Leadframe Package (LLP) and the Power Dissipation and PCB Layout Considerations sections of this datasheet. Note 8: 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 9: The EN pin has an internally connected 1MΩ pull-down resistor Block Diagram 20072203 www.national.com 4 Unless otherwise specified: VIN = 5V, BR-ON = 0V, RSET = Output Current vs. Input Voltage Output Current vs. Input Voltage 20072207 20072210 Output Current vs. Headroom Voltage Output Current vs. Headroom Voltage 20072206 20072213 Output Current vs. Current Set Resistor Quiescent Current vs. Input Voltage (RSET = Open) 20072211 20072217 5 www.national.com LM3595 Typical Performance Characteristics 8.25kΩ, EN = VIN, TA = 25˚C LM3595 Typical Performance Characteristics Unless otherwise specified: VIN = 5V, BR-ON = 0V, RSET = 8.25kΩ, EN = VIN, TA = 25˚C (Continued) Output Current vs. Output Voltage ISET Pin Voltage vs. BRGT Pin Voltage 20072205 20072208 Enable Voltage vs. Input Voltage 20072209 www.national.com 6 LM3595 Detailed Block Diagram 20072204 7 www.national.com LM3595 Circuit Description TABLE 1. IOUT, RSET and VHR-MIN Voltage (BR-ON = 0V), kHR= 30 mV/mA (worst-case) The LM3595 is a parallel white-LED driver with four matched current outputs. This part is intended to be driven off of an existing power supply rail or other regulated voltage source found within the surrounding system. The matched current regulators each have a 100:1 current ratio between the OUTx outputs and the ISET currents. The mirrors control the current through the LEDs without the use of external ballast resistors. With a total of 100mA of total output current available, the LM3595 is easily capable of supplying 25mA per each of the four outputs through the proper selection of the RSET resistor. LED brightness control can be achieved on the LM3595 with a PWM signal and/or an analog voltage. RSET VHEADROOM 12.4kΩ 285mV 15mA 8.25kΩ 430mV 25mA 4.88kΩ 715mV PWM BRIGHTNESS CONTROL Brightness control can be implemented by pulsing a signal at the EN pin. When a PWM signal is used to drive the EN pin of the LM3595, the BR-ON pin should be driven low. The RSET value should be selected using the RSET equation when the analog brightness control feature is disabled. 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 Application Information ENABLE / SHUTDOWN When the voltage on the active-high-logic enable pin is low, the LM3595 will be in shutdown. While disabled, the LM3595 typically draws 0.1µA. When the EN pin is unconnected, the part automatically goes into shutdown due to an internal 1MΩ pull-down resistor that is tied between EN and GND. If the PWM frequency is much less than 100Hz, flicker may be seen in the LEDs. For the LM3595, 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. IOUT being half the programmed LED current. RSET should be chosen not to exceed the maximum current delivery capability of the device. OUTPUT CURRENT CAPABILITY The LM3595 is capable of providing up to 25mA of current to each of the four outputs given an input voltage of 3.0V to 5.5V. The outputs have a typical current matching of 0.5% between adjacent sources. An external resistor can be used to set the output current, as approximated with the following the equation: RSET=100 x (1.22V / IOUTX ) with BR-ON = 0V In order for the output currents to be regulated properly, sufficient headroom voltage (VHR) must be present. The headroom voltage refers to the minimum amount of voltage that must be present across the current source in order to ensure the desired current is realizable. To ensure the desired current is obtained, apply the following equations to find the minimum input voltage required: VIN - VOUTX ≥ VHR ANALOG BRIGHTNESS CONTROL The LM3595 allows for analog brightness control using the BR-ON, and BRGT pin. To enable this function, the BR-ON pin must be set to a voltage greater or equal to 0.45*VIN. With analog brightness enabled, the voltage delivered to pin BRGT can be used to adjust the output currents. Use the maximum desired current (IOUTX(max)) and the maximum analog voltage to be used in the adjustment (V(BR)(max) ) to size RSET according to the following equation: VOUTX is the diode forward voltage, and VHR is defined by the following equation: VHR = kHR x (0.95 x IOUTX) IOUTX is the desired diode current, and kHR, typically 23mV/mA in the LM3595, is a proportionality constant that represents the ON-resistance of the internal current mirror transistors. For worst-case design calculations, using a kHR of 30mV/mA is recommended. (Worst-case recommendation accounts for parameter shifts from part-to-part variation and applies over the full operating temperature range). Changes in headroom voltage from one output to the next, possible with LED forward voltage mismatch, will result in different output currents and LED brightness mismatch. Thus, operating the LM3595 with insufficient headroom voltage across all current sources should be avoided. www.national.com IOUT 10mA Table 2 shows the current through each LED for the LM3595 with various BRGT and RSET values. When analog brightness is used, applying 0V to the BRGT pin does not turn the LEDs off completely. There is a small amount of leakage current (100µA) that typically causes a small amount of light to be emitted from the LED. In order to completely turn off the LEDs, drive the EN pin low to disable the part. 8 LM3595 Application Information (Continued) TABLE 2. LED Current when using the BRGT input with BR-ON = VIN RSET (Ω) 4.99kΩ 6.25kΩ 8.25kΩ 12.4kΩ VBRGT(V) ILED(mA) ILED(mA) ILED(mA) ILED(mA) 0.0 0.1 0.1 0.1 0.1 0.5 4.1 3.3 2.5 1.6 1.0 8.1 6.7 4.9 3.3 1.5 12.2 10.0 7.4 4.9 2.0 16.3 13.3 9.9 6.6 2.5 20.4 16.7 12.3 8.2 3.0 24.5 20.0 14.8 9.8 LED SELECTION parallel connected LEDs. For example, if 30mA is the desired drive current for 2 parallel connected LEDs, RSET and VBRGTshould be selected so that the current through each of the outputs is 15mA. Other combinations of parallel outputs may be implemented in similar fashions, such as in Figure 2. The LM3595 is designed to drive white-LEDs with a typical forward voltage of 3.0V to 4.0V. The maximum LED forward voltage that the LM3595 can accommodate is highly dependant upon VIN and IOUTX. (See the section on Output Current Capability for more information on finding maximum VOUTX.) For applications that demand color and brightness matching, care must be taken to select LEDs from the same chromaticity group. Forward current matching is assured over the LED process variations due to the constant current outputs of the LM3595. TABLE 3. White LED Selection: Component Manufacture Contact Manufacturer Contact Osram www.osram-os.com Nichia www.nichia.com PARALLEL OUTx OUTPUTS FOR INCREASED CURRENT DRIVE 20072216 Outputs OUT1 through OUT4 may be connected together in any combination to drive higher currents through fewer LEDs. For example in Figure 1, outputs OUT1 and OUT2 are connected together to drive one LED while OUT3 and OUT4 are connected together to drive a second LED. FIGURE 2. One Parallel Connected LED Connecting outputs in parallel does not affect internal operation of the LM3595 and has no impact on the Electrical Characteristics and limits previously presented. The available diode output current, maximum diode voltage, and all other specifications provided in the Electrical Characteristics table apply to parallel output configurations, just as they do to the standard 4-LED application circuit. POWER DISSIPATION The maximum allowable power dissipation that this package is capable of handling can be determined as follows: PDMax = (TJMax - TA) / θJA Where TJMAX is the maximum junction temperature, TA is the ambient temperature, and θJA is the junction-to-ambient thermal resistance of the specified package. The LM3595 come in the LLP-10 package that has a junction-to-ambient thermal resistance (θJA) equal to 55˚C/W. This value of θJA is highly dependant upon the layout of the PC board (See the PCB Layout Considerations section of this datasheet for more information). The actual power dissipated by the LM3595 follows the equation: PDISS=(VINx IIN) - N(VOUTX x IOUTX) Where N equals the number of active outputs, VOUTX is the LED forward voltage, and IOUTX is the current supplied to the 20072215 FIGURE 1. Two Parallel Connected LEDs With this configuration, two parallel current sources of equal value provide current to each LED. RSET and VBRGT should therefore be chosen so that the current through each output is programmed to 50% of the desired current through the 9 www.national.com LM3595 Application Information diode by the LM3595. Power dissipation must be less than that allowed by the package. Please refer to the Absolute Maximum Rating of the LM3595. power dissipation. The device will recover and operate normally when the junction temperature falls below the maximum operating junction temperature of 105˚C. It is important to have good thermal conduction with a proper layout to reduce thermal resistance. INPUT CAPACITOR SELECTION PCB LAYOUT CONSIDERATIONS The LM3595 is designed to run off of a fixed input voltage. Depending on the stability and condition of this voltage rail, it may be necessary to add a small input capacitor to help filter out any noise that may be present on the line. In the event that filtering is needed, surface-mount multi-layer ceramic capacitors are recommended. These capacitors are small and inexpensive. A capacitance of 1µF is typically sufficient. The LLP is a leadframe based Chip Scale Package (CSP) with very good thermal properties. This package has an exposed DAP (die attach pad) at the center of the package measuring 2.0mm x 1.2mm. The main advantage of this exposed DAP is to offer lower thermal resistance when it is soldered to the thermal land on the PCB. For PCB layout, National highly recommends a 1:1 ratio between the package and the PCB thermal land. To further enhance thermal conductivity, the PCB thermal land may include vias to a ground plane. For more detailed instructions on mounting LLP packages, please refer to National Semiconductor Application Note AN-1187. (Continued) THERMAL PROTECTION The LM3595 has internal thermal protection circuitry to disable the part if the junction temperature exceeds 150˚C. This feature will protect the device from damage due to excessive www.national.com 10 LM3595 Parallel White-LED Driver Physical Dimensions inches (millimeters) unless otherwise noted 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. 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