High-Brightness LED Drivers <ul><li>Source: MAXIM </li></ul>
Introduction <ul><li>Purpose </li></ul><ul><ul><li>This training module provides an introduction of current driver ICs for...
Background  on High-Brightness LEDs  <ul><li>High-brightness (HB) LEDs are PN-junction devices especially processed to pro...
LED Driving Method 1 <ul><li>Resistor </li></ul><ul><ul><li>A simple biasing circuit that maintains the current at a reaso...
LED Driving Method 2 <ul><li>Linear Current Regulator </li></ul>Current-Sensing Resistor Zener Diode
LED Driving Method 3 <ul><li>Switching-mode Current Regulator   </li></ul><ul><ul><li>Buck: an output voltage is lower tha...
Comparison of LED Driving Methods <ul><li>Has higher cost than the resistor and linear-control methods.  </li></ul><ul><li...
MAX168xx LED Drivers Overview <ul><li>Full range of linear and switch-mode topologies </li></ul><ul><li>Wide input voltage...
Select Table – Linear HB LED Drivers 16-TQFN 1:80 0.35 6.5 to 40    Y Y MAX16836 16-TQFN 1:80 0.35 6.5 to 40    Y Y MAX168...
Select Table – Switch Mode HB LED Drivers 32-TQFN 1:1000 500K 10 5.5 to 76 Boost, buck- boost, buck SEPIC Y Y Y Y MAX16831...
Applications
Interior Lighting in Automotive Applications <ul><li>The   MAX16800   current   regulator   operates   from   a   6.5V   t...
Display Backlighting in Automotive Applications <ul><li>The   MAX16807/MAX16808   LED   drivers   include   eight   LED   ...
Exterior Lighting in Automotive Applications <ul><li>The   MAX16818   LED   driver   utilizes   average-current-mode   con...
Additional Resource <ul><li>For ordering the HB LED dirvers, please click the part list or </li></ul><ul><li>Call our sale...
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High-Brightness LED Drivers

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Introduction of current driver ICs for high-brightness LEDs and their features, and discuss the selection of different products in terms of applications

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  • Welcome to the training module on MAXIM high-brightness LED drivers. This module intends to provide you with an overview of the high-brightness LED driver ICs. You will learn about basic three types of LED driving methods, and selection of different products in terms of applications.
  • In recent years, high-brightness (HB) LEDs have gained prominence as the lighting source for a variety of applications. HB LEDs are rugged and reliable semiconductor devices capable of several tens of thousands of cycles — up to 100,000 hours of operation. That performance represents an operating life that is orders of magnitude longer than conventional incandescent and halogen lamps. Thus, HB-LED applications can be found in automotive lighting, public and commercial signage, and architectural lighting. HB LEDs are PN-junction devices especially processed to produce white, red, green, and blue light when forward biased.
  • As PN-junction devices, LEDs exhibit V-I characteristics similar to those of conventional diodes, but with higher voltage drops across their junctions. Little current passes through an LED until the forward voltage reaches V F , which varies from 2.5V for red LEDs to about 4.5V for blue LEDs. When V F is reached, the current increases very rapidly (as in conventional diodes). Consequently, the designer must employ current limiting to prevent possible damage. LEDs are current-driven devices in which the light output depends directly on the forward current passing through them. A simple biasing circuit that maintains the current (and consequently the light output) at a reasonably constant value, matches the intended power supply with a single current-limiting resistor connected in series with the LED.
  • A simple constant current regulator uses an operational amplifier with an input voltage range that extends to the negative rail. The voltage drop across a current sensing resistor is compared to the reference voltage and the amplifier output voltage rises or falls to control the current. The voltage reference can be a Zener diode. The Zener diode generally has a smallest temperature coefficient and lowest dynamic impedance at a breakdown voltage. Linear regulators are step-down regulators only; that is the input voltage source must be higher than the desired output voltage.
  • The basic switch regulator uses a transistor as a switch that alternately connects and disconnects the input voltage to an inductor. The current pulses are smoothed by the external inductor, diode and capacitor. Current feedback from the sense resistor requires more components than shown here, but the basic principle is the same. The current is compared with a reference and the output of the regulator and the output of the regulator adjusts itself to keep the LED current constant despite falling battery voltage or rising LED temperature.
  • As PN-junction devices, LEDs exhibit V-I characteristics similar to those of conventional diodes, but with higher voltage drops across their junctions. Little current passes through an LED until the forward voltage reaches V F , which varies from 2.5V for red LEDs to about 4.5V for blue LEDs. When V F is reached, the current increases very rapidly (as in conventional diodes). Consequently, the designer must employ current limiting to prevent possible damage. LED driving can be implemented with three basic methods. The table shows advantages and disadvantages of each method.
  • Maxim’s high-brightness LED drivers include 25 products covering the full range of linear and switch-mode topologies, such as boost, buck, flyback and SEPIC. The family contains all the circuitry required for the design of wide-input-voltage-range LED drivers for general lighting and display applications. Each ICs in this family is able to drive multiple LEDs, even the MAX16809/10 LED drivers contain 16 constant-current output channels. The dedicated PWM inputs control the duty cycle of the output current, allowing a wide LED dimming range to be implemented. These devices operate up to 2MHz switching frequency, thus allowing for optimization of the magnetic and filter components, resulting in compact size. Additional features include adjustable constant output current, short-circuit protection and thermal protections.
  • Here is the selection table for linear high-brightness LED drivers.
  • Here is the selection table for switch-mode high-brightness LED drivers.
  • These HB LED drivers are dedicated integrated circuits for white or RGB LEDs. They are energy-saving, cost-effective choices that enable the next generation of LCD backlighting, projection, automotive, and general lighting applications.
  • Interior lighting applications include cluster or instrument backlighting, dome or map reading lights and courtesy lights at doors or in the trunk. All these interior light applications can use LEDs as a light source. While map and dome lighting are often implemented with one LED, cluster and courtesy lighting normally require more than one LED connected in series. All the applications need a regulated constant-current source with an integrated dimming function. The MAX16800 has a high-input voltage range (up to 40V), so it can connect directly to the car battery without needing further protection against voltage surges caused by load dumps on the battery network. The device generates a constant current for the LEDs that can be set by the sense resistor, R SENSE , in series with the LEDs. The color of an LED varies with the current flowing through it. Dimming LED brightness is therefore better achieved by pulse-width modulating (PWM) a constant current than by actually changing the current magnitude. The MAX16800 dims LED brightness by applying a PWM signal to the enable input. The current through the LEDs is turned on and off at the rate set by the PWM signal. In order to reduce the radiated EMI during PWM dimming the MAX16800 uses wave-shaping circuitry to smooth the switching edges.
  • Today more and more liquid crystal displays (LCDs) are used to display information in instrument clusters, car computers, radio and navigation systems, and entertainment systems. Moreover, display backlighting diffuses light across a large area instead of generating a focused light beam. LCD backlingting is to use a matrix of LEDs, providing homogenous illumination and color over the full area. The MAX16807/MAX16808 can be used in buck, boost, or SEPIC mode depending on the input voltage range and the number of LEDs in series per output string. Adding an external resistor and a Zener diode (D) makes the device load-dump proof. While the current through all strings is set by only one resistor, the current of each string is regulated individually. This architecture achieves better than 3% current matching between the individual strings without needing additional external components. While each string can be dimmed individually to adjust for binning mismatches, all strings can be dimmed together through the enable pin. With a dimming frequency range of 50Hz to 30kHz, a dimming ratio of 5000:1 can be achieved. This high ratio is necessary for automotive displays that must be viewable both in the dark and sunlight. The adjustable switching-frequency range from 20kHz to 1MHz makes it possible to select a frequency that will not interfere with other systems like radio receivers.
  • Exterior lighting applications raise new issues of security and safety, and demands for even more high-power illumination, such as taillights and emergency warning lights. Taillight lights need to be visible over long distance but must not illuminate a wide area. The MAX16800/MAX16807/MAX16808 power supplies are also appropriate for this application. Because the number of LEDs in a taillight is typically higher than in the interior applications, more than one of these power supplies will be needed. Multiple power supplies also provide the necessary redundancy to guarantee operation even if one of the circuits fails. Very high-brightness LEDs must be used for applications that require high illumination power like floodlights or fog lights. HB LEDs require very high currents, so the MAX16818 is the solution for these HB LEDs applications. It can provide up to 30A of current. Exterior lighting applications must typically turn on fast or switch brightness instantaneously. To achieve this, the MAX16818 is the first LED driver that uses Maxim&apos;s average-current-mode-control technology for fast LED current transients of up to 20A/µs.
  • Thank you for taking the time to view this presentation on MAXIM high-brightness LED drivers. If you would like to learn more or go on to purchase some of these devices, you can either click on the part list link, or simple call our sales hotline. For more technical information you can either visit the MAXIM site – link shown – or if you would prefer to speak to someone live, please call our hotline number shown, or even use our ‘live chat’ online facility.
  • High-Brightness LED Drivers

    1. 1. High-Brightness LED Drivers <ul><li>Source: MAXIM </li></ul>
    2. 2. Introduction <ul><li>Purpose </li></ul><ul><ul><li>This training module provides an introduction of current driver ICs for high-brightness LEDs and their features, and discuss the selection of different products in terms of applications. </li></ul></ul><ul><li>Outline </li></ul><ul><ul><li>Background on high-brightness LEDs </li></ul></ul><ul><ul><li>Three types of LED driving methods </li></ul></ul><ul><ul><li>Selection table </li></ul></ul><ul><ul><li>Automotive applications </li></ul></ul><ul><li>Contents </li></ul><ul><ul><li>14 pages </li></ul></ul><ul><li>Duration </li></ul><ul><ul><li>10 Minutes </li></ul></ul>
    3. 3. Background on High-Brightness LEDs <ul><li>High-brightness (HB) LEDs are PN-junction devices especially processed to produce white, red, green and blue light. </li></ul><ul><li>HB LEDs are rugged and reliable semiconductor devices. </li></ul><ul><li>HB LEDs have up to 100,000 hours of operation. </li></ul><ul><li>HB LEDs have longer lifetime than conventional incandescent and halogen lamps. </li></ul><ul><li>HB-LED applications include: </li></ul><ul><ul><li>Automotive lighting </li></ul></ul><ul><ul><li>Public and commercial signage </li></ul></ul><ul><ul><li>Architectural lighting </li></ul></ul>
    4. 4. LED Driving Method 1 <ul><li>Resistor </li></ul><ul><ul><li>A simple biasing circuit that maintains the current at a reasonably constant value. </li></ul></ul>
    5. 5. LED Driving Method 2 <ul><li>Linear Current Regulator </li></ul>Current-Sensing Resistor Zener Diode
    6. 6. LED Driving Method 3 <ul><li>Switching-mode Current Regulator </li></ul><ul><ul><li>Buck: an output voltage is lower than the input </li></ul></ul><ul><ul><li>Boost: an output voltage is higher that the input </li></ul></ul><ul><ul><li>Buck-boost: an output voltage is opposite in polarity to the input </li></ul></ul><ul><ul><li>Flyback: an output voltage that is less than or greater than the input can be generated </li></ul></ul>Boost Regulator Current Sensing Resistor V REF Pulse Width Modulator
    7. 7. Comparison of LED Driving Methods <ul><li>Has higher cost than the resistor and linear-control methods. </li></ul><ul><li>Careful design is necessary to allay EMI considerations. </li></ul><ul><li>Active circuitry may require more area, but the other methods may require more hardware and physical space for cooling. </li></ul><ul><li>Control loop regulates LED current precisely. </li></ul><ul><li>Allows dimming by amplitude control or low-frequency PWM. </li></ul><ul><li>Allows automatic temperature compensation of LED characteristics. </li></ul><ul><li>Allows efficient operation over a wide input-voltage range. </li></ul><ul><li>Does not usually have mechanical heatsinking </li></ul>Switching Regulator Control <ul><li>Is more expensive than the simple resistive current limiter </li></ul><ul><li>For the same supply voltage, dissipates about the same power as a resistor limiter. </li></ul><ul><li>May require mechanical heatsinking of the active pass device. </li></ul><ul><li>Linear control-loop circuitry accurately controls the LED current. </li></ul><ul><li>Allows dimming through current control. </li></ul><ul><li>Allows dimming through control of amplitude or low-frequency PWM. </li></ul><ul><li>Allows automatic temperature compensation of LED characteristics. </li></ul>Linear Control <ul><li>It cannot control current accurately. </li></ul><ul><li>Current varies to some extent with supply voltage. </li></ul><ul><li>High power dissipation </li></ul><ul><li>Inexpensive </li></ul><ul><li>Only one, large component </li></ul>Resistor Disadvantages Advantages LED Driving Method
    8. 8. MAX168xx LED Drivers Overview <ul><li>Full range of linear and switch-mode topologies </li></ul><ul><li>Wide input voltage range: 4.5V to 76V </li></ul><ul><li>Multiple independent channels </li></ul><ul><li>PWM for white or RGB dimming </li></ul><ul><li>Up to 2MHz switching frequency </li></ul><ul><li>Integrated short circuit protection, and thermal shutdown capability </li></ul><ul><li>Adjustable constant LED current </li></ul>
    9. 9. Select Table – Linear HB LED Drivers 16-TQFN 1:80 0.35 6.5 to 40   Y Y MAX16836 16-TQFN 1:80 0.35 6.5 to 40   Y Y MAX16835 6-TDFN 1:100 0.3 6.5 to 40   Y Y MAX16828 16-TSSOP 1:5000 0.15/ch 6.5 to 28 Y Y Y MAX16825 16-TSSOP 1:5000 0.15/ch 6.5 to 28 Y Y Y MAX16824 16-TQFN/TSSOP 1:200 0.07/ch 5.5 to 40   Y Y MAX16823 6-TDFN 1:100 0.1 6.5 to 40   Y Y MAX16815 20-TQFN 1:200 0.35 5.5 to 40   Y Y MAX16806 20-TQFN 1:200 0.35 5.5 to 40   Y Y MAX16805 20-TQFN 1:200 0.35 5.5 to 40   Y Y MAX16804 16-TQFN 1:200 0.35 6.5 to 40 Y Y Y MAX16803 16-TQFN 1:30 0.35 6.5 to 40   Y Y MAX16800 Display Backlighting General Lighting Automotive Lighting Package PWM Dimming Ratio I LED (A,max) V IN (V) Applications Part
    10. 10. Select Table – Switch Mode HB LED Drivers 32-TQFN 1:1000 500K 10 5.5 to 76 Boost, buck- boost, buck SEPIC Y Y Y Y MAX16831 28-TQFN 1:5000 125K - 1.5M 30 4.75 to 5.5, 7 to 28 Boost, buck- boost, buck SEPIC   Y Y Y MAX16821 6-TDFN 1:5000 20K to 2M 3 4.5 to 28 Buck     Y Y MAX16820 6-TDFN 1:5000 20K to 2M 3 4.5 to 28 Buck     Y Y MAX16819 28-TQFN 1:5000 125K - 1.5M 30 7 to 28 Buck Y Y   Y MAX16818 32-TQFN 1:1000 500K 10 5.5 to 76 Boost, buck- boost,buck, SEPIC   Y Y Y MAX16816 28-TQFN 1:100 125K - 500K 0.5 6.5 to 76 Boost, buck-boost, Buck   Y Y Y MAX16812 38-TQFN 1:5000 20K to 1M 0.05/ch 8 to 26.5 Boost, SEPIC + 16 linear Y       MAX16809 MAX16810 28-TSSOP-EP 1:5000 20K to 1M 0.05/ch 8 to 26.5 Boost, SEPIC + 8 linear Y       MAX16807 MAX16808 8-μMAX 1:3000 262K 10 10.8 to 24 Boost, Buck, flyback, SEPIC     Y   MAX16802 8-μMAX 1:3000 262K 10 10.8 to 24 Boost, flyback, SEPIC     Y   MAX16801 Display Backlighting Projection General Lighting Automotive Lighting Package PWM Dimming Ratio Frequency (Hz) ILED (A, max) VIN (V) Topology Applications Part
    11. 11. Applications
    12. 12. Interior Lighting in Automotive Applications <ul><li>The MAX16800 current regulator operates from a 6.5V to 40V input voltage range and delivers up to a total of 350mA to one or more strings of HB LEDs. </li></ul>
    13. 13. Display Backlighting in Automotive Applications <ul><li>The MAX16807/MAX16808 LED drivers include eight LED driver outputs rated for 36V continuous operation. The LED current-control circuitry achieves ±3% current matching among strings and enables paralleling of outputs for LED string currents higher than 55mA. </li></ul>
    14. 14. Exterior Lighting in Automotive Applications <ul><li>The MAX16818 LED driver utilizes average-current-mode control that enables optimal use of MOSFETs with optimal charge and on-resistance characteristics. This minimizes the need for external heatsinking even when delivering up to 30A of LED current. </li></ul>
    15. 15. Additional Resource <ul><li>For ordering the HB LED dirvers, please click the part list or </li></ul><ul><li>Call our sales hotline </li></ul><ul><li>For additional inquires contact our technical service hotline </li></ul><ul><li>For more product information go to </li></ul><ul><ul><li>http://para.maxim-ic.com/search.mvp?fam=hbled&hs=1 </li></ul></ul>

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