CAT32 CMOS White LED Driver Description The CAT32 is a DC/DC step up converter that delivers a regulated output current. Operation at a constant switching frequency of 1.2 MHz allows the device to be used with very small value external inductor and ceramic capacitors. The CAT32 is targeted to drive multiple white light−emitting diodes (LEDs) connected in series and provides the necessary regulated current to control the brightness and the color purity. An external resistor RSET controls the output current level. LED currents of up to 40 mA can be supported over a wide range of input supply voltages from 2 V to 7 V, making the device ideal for battery−powered applications. A high voltage output stage allows up to 4 White LEDs to be driven in series. Series drive provides inherent current matching. LED dimming can be done by using a DC voltage, a logic signal, or a pulse width modulation (PWM) signal. The shutdown input pin allows the device to be placed in power−down mode with “near zero” quiescent current. In addition to overcurrent limiting protection, the device also includes detection circuitry to ensure protection against open−circuit load fault conditions. The device is available in a low profile (1 mm max height) 6−lead TSOT−23 package. http://onsemi.com 1 TSOT−23 TD SUFFIX CASE 419AF PIN CONNECTIONS 1 GND SHDN LED RSET TSOT−23 1 mm Maximum Height qJA = 250°C/W (free air) (Top View) Features • • • • • • • • • • • • • Low Quiescent Ground Current (0.5 mA Typical) Power Efficiency Over 80% Compatible Pinout with LT1932 Adjustable Output Current (up to 40 mA) High Frequency 1.2 MHz Operation Input Voltage Operation down to 2.0 V Low Resistance (0.5 W) High Voltage Power Switch Drives up to 4 White LEDs in Series Shutdown Current Less than 1 mA Load Fault Protection Against Open−circuits Low Value External Components Low Profile (1 mm) TSOT−23 6−lead Package These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS Compliant Applications • • • • • • Color LCD and Keypad Backlighting Cellular Phones Handheld Terminals Digital Cameras PDAs/Games Portable MP3 Players © Semiconductor Components Industries, LLC, 2010 March, 2010 − Rev. 4 VIN SW 1 MARKING DIAGRAMS VFYM LLYM LL = CAT32TDI−T3 VF = CAT32TDI−GT3 Y = Production Year (Last Digit) M = Production Month (1−9, A, B, C) ORDERING INFORMATION Device Package Shipping CAT32TDI−T3 TSOT−23 (Pb−Free) 3,000/ Tape & Reel CAT32TDI−GT3 TSOT−23 (Pb−Free) 3,000/ Tape & Reel Publication Order Number: CAT32/D CAT32 Typical Application Circuit D1 L1 6.8 mH VIN 2.7 V to 4.2 V C1 4.7 mF 1 SW 6 VIN PWM DIMMING CONTROL C1: Taiyo Yuden JMK212BJ475 C2: Taiyo Yuden EMK212BJ105 D1: Zetez ZHCS400 L1: Sumida CLQ4D106R8 (Panasonic ELJEA6R8) CAT32 5 LED SHDN RSET 4 RSET 1.50 kW TSOT−23 Pin Numbers GND 2 3 C2 1 mF 15 mA Figure 1. Li−Ion Driver for Four High−Brightness White LEDs Table 1. PIN DESCRIPTION Pin Number SOT23 Pin Number TDFN Name Function 1 8 SW Switch pin. This is the drain of the internal power switch. For minimum EMI, minimize the trace area connected to this pin. 2 5 GND Ground pin. Connect pin 2 to ground. 3 6 LED LED (cathode) connection pin. 4 4 RSET 5 3 SHDN 6 2 VIN − 1 Power Ground RESET pin. A resistor connected from pin 4 to ground sets the LED current. This pin is also used to dim the LEDs. Shutdown pin. Input supply pin. This pin should be bypassed with a capacitor to ground. A 4.7 mF capacitor mounted close to the pin is recommended. Power Ground http://onsemi.com 2 CAT32 Table 2. ABSOLUTE MAXIMUM RATINGS Parameter Rating Unit VIN, LED, SHDN voltage 8 V SW voltage 20 V RSET voltage 1 V Storage Temperature Range −65 to +150 °C Junction Temperature 125 °C Lead Soldering Temperature (10 secs) 300 °C ESD Rating – Human Body Model 2000 V Stresses exceeding Maximum Ratings may damage the device. Maximum Ratings are stress ratings only. Functional operation above the Recommended Operating Conditions is not implied. Extended exposure to stresses above the Recommended Operating Conditions may affect device reliability. Table 3. RECOMMENDED OPERATING CONDITIONS Parameter Range Unit 2 to 7 V −40 to +85 °C Inductor L1 6.8 ±20% typical mH Input Capacitor C1 4.7 ±20% typical mF Output Capacitor C2 1.0 ±20% typical mF 0 to 20 mA VIN Ambient Temperature Range ILED with 1 to 4 LEDs in series NOTE: Typical application circuit with external components is shown on page 2. Table 4. ELECTRICAL OPERATING CHARACTERISTICS (Over recommended operating conditions unless otherwise specified. TA = 25°C, VIN = 2 V and VSHDN = 1.2 V.) Symbol IQ Parameter IGND Ground Current in Shutdown VLED LED Pin Voltage ILED LED Current Adjust Range ILED Programmed LED Current ILED VRSET Typ Max Unit VRSET = 0.2 V Conditions 0.5 0.7 mA VSHDN = 0 V 0.05 1 mA VIN < VOUT, ILED = 15 mA 120 180 mV 40 mA 45 mA Quiescent Current Min 5 33 38 RSET = 750 W 25 30 36 RSET = 1.5 kW 12.5 15 17.5 RSET = 562 W RSET = 4.53 kW 5 LED Pin Current Temperature Coefficient ILED = 15 mA −0.01 mA/°C RSET Pin Voltage RSET = 1.5 kW 100 mV Shutdown Pin Logic High Level 0.85 V Shutdown Pin Logic Low Level 0.25 V fSW Boost Converter Frequency 0.8 1.2 1.6 MHz ISWL Switch Current Limit 400 550 780 mA RSW Switch Resistance VIN = 2 V, ISW = 100 mA 0.7 1.2 W VIN = 3 V, ISW = 100 mA 0.5 0.9 Switch Off, VSW = 5 V 0.01 5 Components shown on Figure 1 83 Switch Leakage Current Efficiency http://onsemi.com 3 mA % CAT32 TYPICAL CHARACTERISTICS (VIN = 3.6 V, TAMB = 25°C, CIN = 4.7 mF, COUT = 1 mF, L = 6.8 mH, unless otherwise specified.) 600 QUIESCENT CURRENT (mA) QUIESCENT CURRENT (mA) 600 500 400 300 200 2 3 4 5 6 −25 0 25 50 75 100 125 TEMPERATURE (°C) Figure 2. Quiescent Current vs. Input Voltage Figure 3. Quiescent Current vs. Temperature 2.0 SWITCH FREQUENCY (MHz) SWITCH FREQUENCY (MHz) 300 INPUT VOLTAGE (V) 1.6 1.2 0.8 0.4 2 3 4 5 6 1.6 1.2 0.8 0.4 0 −50 7 −25 0 25 50 75 100 INPUT VOLTAGE (V) TEMPERATURE (°C) Figure 4. Switching Frequency vs. Input Voltage Figure 5. Switching Frequency vs. Temperature 35 125 20 LED CURRENT (mA) RSET = 750 W 30 LED CURRENT (mA) VIN = 2 V 400 200 −50 7 2.0 0 VIN = 7 V 500 25 RSET = 1.13 kW 20 RSET = 1.50 kW 15 RSET = 2.26 kW 10 15 10 5 5 0 2 3 4 5 6 0 −50 7 −25 0 25 50 75 100 INPUT VOLTAGE (V) TEMPERATURE (°C) Figure 6. LED Current vs. Input Voltage Figure 7. LED Current vs. Temperature http://onsemi.com 4 125 CAT32 TYPICAL CHARACTERISTICS (VIN = 3.6 V, TAMB = 25°C, CIN = 4.7 mF, COUT = 1 mF, L = 6.8 mH, unless otherwise specified.) 1.0 SWITCH RESISTANCE (W) SWITCH RESISTANCE (W) 1.0 0.8 0.6 0.4 0.2 0 2 3 4 5 0.8 0.6 VIN = 3 V 0.4 0.2 0 −50 6 −25 0 25 50 75 100 125 INPUT VOLTAGE (V) TEMPERATURE (°C) Figure 8. Switch Resistance vs. Input Voltage Figure 9. Switch Resistance vs. Temperature LED PIN VOLTAGE (mV) 300 250 200 150 100 50 0 0 8 16 24 32 40 LED CURRENT (mA) Figure 10. LED Pin Voltage vs. LED Current Figure 11. VSW, IL, & VOUT Signal Waveforms 85 EFFICIENCY (%) 80 75 4 LEDs at 15 mA VOUT = 13 V 70 65 60 2 3 4 5 6 INPUT VOLTAGE (V) Figure 12. Efficiency vs. Input Voltage Figure 13. PWM on SHDN Pin Waveform http://onsemi.com 5 CAT32 Operation The CAT32 device is a high efficiency, constant frequency, current regulating boost converter. The device includes a switch and an internally compensated loop for the regulation of the LED current. Operation can be best understood by examining the block diagram. The RSET pin is regulated at 100 mV and the current through the external resistor will set the regulated current in the LEDs (from 5 mA to 40 mA) with a multiplication factor of 225. While maintaining LED current regulation, the CAT32 automatically adjusts the LED pin voltage to be as low as possible. A low LED pin voltage ensures high efficiency. Current through the internal power switch is continuously monitored cycle−by−cycle. If the current limit is exceeded, the switch is immediately turned off, protecting the device, for the remainder of the cycle. PWM dimming operation can be achieved by switching the SHDN pin or by pulling the RSET pin higher than 0.1 V. Block Diagram L1 VIN D1 C2 1 C1 SW Over Voltage Protection (22 V) 1.2 MHz Oscillator PWM & Logic + Current Sense − Amp 6 VIN 5 SHDN LED − 3 + 100 mV Current Control 225x IS CAT32 GND RSET 2 4 RSET Figure 14. CAT32 Block Diagram http://onsemi.com 6 ILED = 225 x IS ILED CAT32 Application Information Inductor Selection and Efficiency Inductor vendors are shown below. Contact the manufacturer for detailed technical data and new product information. Table 5. INDUCTOR MANUFACTURERS L (mH) Maximum DCR (mW) Maximum Height (mm) ELJEA4R7 4.7 180 2.2 ELJEA6R8 6.8 250 2.2 4.7 260 2.2 10 300 2.2 LB2016B4R7 4.7 250 2.0 LB2016B100 3.8 350 2.0 CMD4D06−4R7 4.7 216 0.8 CMD4D06−6R8 6.8 296 0.8 CLQ4D10−4R7 4.7 162 1.2 CLQ4D10−6R8 6.8 195 1.2 Inductor LQH3C4R7M24, LQH32CN4R7M11 LQH3C100K24, LQH32CN100K11 Vendor Web Panasonic 714.373.7334 www.panasonic.com Murata 770.436.1300 www.murata.com Taiyo Yuden 408.573.4150 www.t−yuden.com Sumida 847.956.0666 www.sumida.com Capacitor Selection Diode Selection Low ESR (equivalent series resistance) capacitors should be used at the output to minimize the output ripple voltage. The low ESR and small package options available with multilayer ceramic capacitors make them excellent choices. The X5R and X7R capacitor types are preferred because they retain their capacitance over wider voltage and temperature ranges than the Y5V or Z5U types. A 1.0 mF or 2.2 mF output capacitor is recommended for most applications. The voltage rating of the output capacitor C2 depends on the number of LEDs driven in series. A 10 V ceramic capacitor is recommended when driving two LEDs. A 16 V ceramic capacitor is recommended when driving 3 or 4 LEDs. Schottky diodes, with their low forward voltage drop and fast switching speed, are the ideal choice for high efficiency applications. Table 7 shows several different Schottky diodes that work well with the CAT32. Make sure that the diode has a voltage rating greater than the output voltage. The diode conducts current only when the power switch is turned off (typically less than one−third the time), so a 0.4 A or 0.5 A diode will be sufficient for most designs. Table 7. SCHOTTKY DIODE SUPPLIERS Part MBR0520 MBR0540 ON Semiconductor www.onsemi.com 800.282.9855 ZHCS400 Zetex MBR0530 s Table 6. CERAMIC CAPACITOR MANUFACTURERS Supplier Supplier Phone Web Taiyo Yuden 408.573.4150 www.t−yuden.com LED Current Programming Murata 814.237.1431 www.murata.com Kemet 408.986.0424 www.kemet.com The LED current is programmed with a single resistor connected to the RSET pin. The RSET pin is internally regulated to 100 mV, which sets the current flowing out of this pin, ISET, equal to 100 mV/RSET. The CAT32 regulates the current into the LED pin, ILED, to 225 times the value of ISET. For the best accuracy, a 1% or better resistor is recommended. Table 8 shows several typical 1% RSET values. Low profile ceramic capacitors with a 1 mm maximum height/thickness are available for designs height requirements. Ceramic capacitors also make a good choice for the input capacitor, which should be mounted as close as possible to the CAT32. A 2.2 mF or 4.7 mF input capacitor is recommended. Table 6 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information as new products and package options are introduced regularly. http://onsemi.com 7 CAT32 In addition to providing the widest dimming range, PWM brightness control also ensures the “purest” white LED color over the entire dimming range. The true color of a white LED changes with operating current, and is the “purest” white at a specific forward current, usually 15 mA or 20 mA. If the LED current is less than or more than this value, the emitted light becomes more blue. Applications involving color LCDs can find the blue tint objectionable. When a PWM control signal is used to drive the SHDN pin of the CAT32, the LEDs are turned off and on at the PWM frequency. The current through them alternates between full current and zero current, so the average current changes with duty cycle. This ensures that when the LEDs are on, they can be driven at the appropriate current to give the purest white light. LED brightness varies linearly with the PWM duty cycle. Table 8. RSET RESISTOR VALUES ILED (mA) RSET 40 562 W 30 750 W 25 909 W 20 1.13 kW 15 1.50 kW 10 2.26 kW 5 4.53 kW For other LED current values, use the following equation to choose RSET. 0.1 V I LED R SET + 255 Most white LEDs are driven at maximum currents of 15 mA to 20 mA. Some higher power designs will use two parallel strings of LEDs for greater light output, resulting in 30 mA to 40 mA (two strings of 15 mA to 20 mA) flowing into the LED pin. LED Dimming with a Logic Signal For applications that need to adjust the LED brightness in discrete steps, a logic signal can be used. RMIN sets the minimum LED current value (when the NMOS is OFF): LED Dimming with PWM Signal PWM brightness control provides the widest dimming range (greater than 20:1). By turning the LEDs ON and OFF using the control signal the LEDs operate at either zero or full current, but their average current changes with the PWM signal duty cycle. Typically, a 5 kHz to 40 kHz PWM signal is used. PWM dimming with the CAT32 can be accomplished two different ways. The SHDN pin can be driven directly or a resistor can be added to drive the RSET pin. If the SHDN pin is used, increasing the duty cycle will increase the LED brightness. Using this method, the LEDs can be dimmed and turned off completely using the same control signal. A 0% duty cycle signal will turn off the CAT32, reducing the total quiescent current to near zero. If the RSET pin is used, increasing the duty cycle will decrease the brightness. Using this method, the LEDs are dimmed using RSET and turned off completely using SHDN. If the RSET pin is used to provide PWM dimming, the approximate value of RPWM should be calculated (where VMAX is the “HIGH” value of the PWM signal): R PWM + R SET ǒ V MAX *1 0.15 V CAT32 CAT32 SHDN 5 RSET 4 RSET 4 RSET RPWM PWM RSET I LED(MIN) RINCR determines how much LED current increases when the external NMOS switch is turned ON. R INCR + 255 0.1 V I LED(Increase) LED Dimming with a DC Voltage R ADJ + 225 V MAX * 0.1 V I LED(MAX) * I LEAD(MIN) PCB Layout Guidelines The CAT32 is a high−frequency switching regulator and therefore proper PCB board layout and component placement can minimize noise and radiation and increase efficiency. To maximize efficiency, the CAT32 design has fast switch rise and fall times. To prevent radiation and high frequency resonance problems minimize the length and area of all traces connected to the SW pin and use a ground plane under the switching regulator. The switch, schottky output diode and output capacitor signal path should be kept as short as possible. The ground connection for the RSET resistor should be tied directly to the GND pin and not be shared with other components. Ǔ CAT32 PWM 0.1 V R MIN + 255 RPWM 10 kW PWM 0.1 mF CAT32 CAT32 RSET 4 RSET 4 RSET Figure 15. LED Dimming Circuits http://onsemi.com 8 RADJ VDC RMIN RINCR Logic Signal CAT32 TYPICAL APPLICATION CIRCUITS (The application diagrams below are shown for the TSOT−23 packages.) L1 VIN D1 6.8 mH 6 VIN 1 SW CAT32 C1 4.7 mF 5 2.5 V DC DIMMING CONTROL SHDN LED RSET 4 60.40 kW GND 2 C2 2.2 mF 3 15 mA RSET 1.50 kW Figure 16. Two LEDs with DC Level Dimming Control D1 L1 6.8 mH 6 VIN 85 VIN = 4.2 V 1 SW CAT32 C1 4.7 mF 5 2.5 V DC 60.40 kW DIMMING CONTROL VIN = 3.0 V 80 SHDN LED RSET 4 GND 2 C2 3 1 mF 15 mA EFFICIENCY (%) VIN 75 70 65 RSET 1.50 kW 60 0 5 10 15 20 LED CURRENT (mA) Figure 17. Three LEDs with DC Level Dimming Control D1 L1 6.8 mH VIN Figure 18. Efficiency − Three LEDs 85 1 EFFICIENCY (%) 6 SW VIN PWM DIMMING CONTROL VIN = 4.2 V 80 C1 4.7 mF CAT32 5 SHDN RSET 4 RSET 1.50 kW LED GND 2 C2 3 15 mA 1 mF VIN = 3.0 V 75 70 65 60 0 5 10 15 LED CURRENT (mA) Figure 19. Four LEDs with PWM Dimming Control Figure 20. Efficiency − Four LEDs http://onsemi.com 9 20 CAT32 PACKAGE DIMENSIONS TSOT−23, 6 LEAD CASE 419AF−01 ISSUE O SYMBOL D MIN NOM A e E1 MAX 1.00 A1 0.01 0.05 0.10 A2 0.80 0.87 0.90 b 0.30 c 0.12 E 0.45 0.15 D 2.90 BSC E 2.80 BSC E1 1.60 BSC e 0.95 TYP L 0.30 L1 0.40 0.20 0.50 0.60 REF L2 0.25 BSC 0º θ 8º TOP VIEW A2 A b q L A1 c L1 SIDE VIEW END VIEW Notes: (1) All dimensions are in millimeters. Angles in degrees. (2) Complies with JEDEC MO-193. http://onsemi.com 10 L2 CAT32 Example of Ordering Information (Note 3) 1. 2. 3. 4. 5. Prefix Device # Suffix CAT 32 TD I −G T3 Company ID (Optional) Product Number 32 Package TD: TSOT−23 Temperature Range I = Industrial (−40°C to +85°C) Lead Finish G: NiPdAu Tape & Reel (Note 5) T: Tape & Reel 3: 3,000 / Reel All packages are RoHS−compliant (Lead−free, Halogen−free). The standard lead finish is NiPdAu. The device used in the above example is a CAT32TDI−GT3 (TSOT−23, Industrial Temperature Range, NiPdAu, Tape & Reel, 3,000 / Reel). 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