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LM3590 Series White LED Driver
November 2003
LM3590 Series White LED Driver
General Description
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. 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 50A when operating in the no-load condition and draws less than 0.1A when the device is shut down. The LM3590 is available in a small 5-pin SOT23 package.
Features
n n n n 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 (0.1A 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
Typical Application Circuit
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(c) 2003 National Semiconductor Corporation
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LM3590
Connection Diagram
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Ordering Information
Order Number LM3590MF LM3590MFX Package Description SOT23-5 SOT23-5 Package Marking SABB*Z1X SABB*Z1X Supplied As Tape and Reel 250 Units, Tape and Reel 3000 Units, Tape and Reel
Pin Description
Pin # 1 Name ISET Function Programmable LED current Input. The LED current has the following relationship with the resistor used: RSET = 100 x (125 / IOUT) 2 3 4 5 GND IOUT VIN EN Ground Connection Constant Current LED Output Power Supply Voltage Input. Input voltage range: 6V-12.6V Device Enable
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Absolute Maximum Ratings
2)
(Notes 1,
Operating Conditions
Input Voltage Range EN Voltage Range Ambient Temperature (TA) Range (Note 4) Junction Temperature (TJ) Range 6.0V to 12.6V 0V to VIN -40C to +85C
If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN EN Maximum Junction Temperature (TJMAX) Storge Temperature Maximum Lead Temperature (Soldering, 5 sec.) ESD Rating (Note 3) Human Body Model Machine Model 1.5kV 200V -0.3 to 13.0V Max -0.3 to (VIN+0.3V) w/ 13.0V max 150C -65C to +150C 260C
-40C to +110C
Thermal Information
Junction-to-Ambient Thermal Resistance, SOT23-5 Package (JA) (Note 5) 220C/W
Electrical Characteristics (Notes 2, 6)
Limits in standard typeface are for TJ = 25C and limits in boldface type apply over the full Operating Junction Temperature Range (-40C TJ +110C). Unless otherwise specified, CIN = 1 F, VIN = 12.0V, VEN = 3.0V, RSET = 6.19k, VIOUT = 10.8V. Symbol IOUT Parameter Output Current Capability Conditions VIN = 12V 7.5V VIOUT 11.5V VIOUT = 10.8V 11.3V VIN 12.6V RSET = 8.35k RSET = 12.5k Output Current Programming IOUT ratio to ISET IQ Quiescent Supply Current 11.3V VIN 12.6V RSET = OPEN IOUT = OPEN VIN = 12.6V VEN = 0V IOUT = 95% nominal Min 19 (-5%) 19 (-5%) Typ 20 20 15 10 125 / RSET 100:1 50 75 A A Max 21 (+5%) 21 (+5%) mA Units
ISD VISET VHR
Shutdown Supply Current ISET Reference Voltage Minimum Current Source Voltage Headroom (VIN - VIOUT)(Note 7) Logic Input EN: High level Logic Input EN: Low level Enable Pin Input Current(Note 8) Turn-On Time
0.1 1.25 300
1
A V mV
VIH VIL IEN tON
1.1 0 6 IOUT = 90% of steady state 50
VIN 0.3
V V A s
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 1.5k 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 (JA), as given by the following equation: TA-MAX = TJ-MAX-OP - (JA 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.
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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 500k pull-down resistor is connected between the EN and GND pins.
Functional Block Diagram
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Typical Performance Characteristics Unless otherwise specified, CIN = 1F, VIN = 12.0V, VEN = 3.0V, VIOUT = 10.8V, RSET = 6.19k, TA = 25C. CIN is a low ESR multi-layer ceramic capacitor (MLCC).
IOUT vs VIN IOUT vs VIOUT
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IOUT vs RSET
IQ vs VIN
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VSET vs VIN
Shutdown Supply Current vs VIN
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LM3590
Typical Performance Characteristics Unless otherwise specified, CIN = 1F, VIN = 12.0V, VEN = 3.0V, VIOUT = 10.8V, RSET = 6.19k, TA = 25C. CIN is a low ESR multi-layer ceramic capacitor (MLCC). (Continued)
Shutdown Threshold vs VIN Startup
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LM3590
Application Information
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). ENABLE MODE The Enable pin (EN) disables the part and reduces the quiescent current to 0.1A (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 500k 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, 15m 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. TABLE 1. Ceramic Capacitor Manufacturers Manufacturer TDK Murata Taiyo Yuden Contact www.component.tdk.com www.murata.com 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. 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) 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
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required headroom voltage is proportional to the current flowing through the current source, as dictated by the equation: VHR-MIN = kHR x IOUT 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.
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. TABLE 2. White LED Selection Manufacturer Osram Nichia Contact www.osram-os.com www.nichia.com
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
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LM3590
Application Information
2.
(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 = 50s) 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.
the power consumed by the LEDs, TAis the ambient temperature, and JA 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 = (VIN x IOUT) - (VIOUT x IOUT) TJ = TA + (PDISSIPATION x JA) 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 110C. 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 110C.
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 resistance 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.
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FIGURE 2. Example: R1 = 15.8k, R2 = 31.6k, RSET = 31.6k
TABLE 3. Digital LED Current Programming EN 0 1 1 1 1 SET1 X 1 1 0 0 SET2 X 1 0 1 0 RISET Shutdown RSETiR1iR2 RSETiR1 RSETiR2 RSET Example RISET Shutdown 31.6ki15.ki31.6k 31.6ki15.k 31.6ki31.6k 31.6k Example IOUT Shutdown 16mA 12mA 8mA 4mA
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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. 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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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.
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.

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