CAT37 CMOS White LED Driver Boost Converter FEATURES DESCRIPTION Low quiescent ground current (0.5mA typical) The CAT37 is a DC/DC step up converter that delivers a regulated output current. Operation at a constant switching frequency of 1.2MHz allows the device to be used with very small value external inductor and ceramic capacitors. Power efficiency over 80% Compatible pinout with LT1932 Adjustable output current (up to 40mA) High frequency 1.2MHz operation The CAT37 is targeted to drive multiple white lightemitting diodes (LEDs) connected in series and provides the necessary regulated current to control the brightness and the color purity. An external resistor R1 controls the output current level. LED currents of up to 40mA can be supported over a wide range of input supply voltages from 2.5V to 7V, making the device ideal for battery-powered applications. Input voltage operation down to 2.5V Low resistance (0.5Ω) power switch Drives up to 4 White LEDs in series Shutdown current less than 1µA Load fault protection against open-circuits Low value external components Low profile (1mm) TSOT-23 5-lead package A high voltage output stage allows up to 4 White LEDs to be driven in series. Series drive provides inherent current matching. APPLICATION Color LCD and keypad backlighting 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. Cellular phones Handheld terminals Digital cameras PDAs/Games In addition to overcurrent limiting protection, the device also includes detection circuitry to ensure protection against open-circuit load fault conditions. Portable MP3 players For Ordering Information details, see page 11. The device is available in a low profile (1mm max height) 5-lead TSOT-23 package. TYPICAL APPLICATION CIRCUIT L1 6.8µH D1 VIN 3V to 5V C1 1µF 5 VIN C2 1µF 1 SW CAT37 ON OFF 4 FB SHDN GND 2 3 15mA R1 6.34kΩ C1: Taiyo Yuden JMK212BJ475 C2: Taiyo Yuden EMK212BJ105 D1: Zetez ZHCS400 L1: Panasonic ELJEA6R8 or equivalent Figure 1. Driver for Four High-Brightness White LEDs © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 1 Doc. No. MD-5005 Rev. T CAT37 ORDERING INFORMATION Part Number CAT37TDI-T3 CAT37TDI-GT3 Package TSOT-23 5-lead (1) TSOT-23 5-lead (2) Quantity per Reel 3,000 3,000 Package Marking LM UL PIN CONFIGURATION TSOT-23 5-Lead Top View SW 1 GND 2 FB 3 5 VIN 4 SHDN 1mm maximum height θJA = 250ºC/W [free air] PIN DESCRIPTION Pin Number Name 1 SW 2 GND 3 FB 4 ¯¯¯¯¯ SHDN 5 VIN Function Switch pin. This is the drain of the internal power switch. For minimum EMI, minimize the trace area connected to this pin. Ground pin. Connect pin 2 to ground. LED (cathode) connection pin. Shutdown pin. Input supply pin. This pin should be bypassed with a capacitor to ground. A 1µF capacitor mounted close to the pin is recommended. Notes: (1) Matte-Tin Plated Finish (RoHS-compliant). (2) NiPdAu Plated Finish (RoHS-compliant). Doc. No. MD-5005 Rev. T 2 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT37 ABSOLUTE MAXIMUM RATINGS Parameter VIN, FB, ¯¯¯¯¯ SHDN voltage SW voltage Storage Temperature Range Junction Temperature Lead Soldering Temperature (10 secs) ESD Rating – Human Body Model (1) Rating 8 20 -65 to +160 125 300 2000 Unit V V ºC ºC ºC V RECOMMENDED OPERATING CONDITIONS Parameter VIN Ambient Temperature Range Inductor L1 Input Capacitor C1 Output Capacitor C2 ILED with 1 to 4 LEDs in series Range 2.5 to 7 -40 to +85 6.8 ± 20% typical 1.0 ± 20% typical 1.0 ± 20% typical 0 to 20 Unit V °C µH µF µF mA Typical application circuit with external components is shown on page 1. ELECTRICAL OPERATING CHARACTERISTICS Over recommended operating conditions unless otherwise specified. TA = 25ºC, VIN = 3V and V¯¯¯¯¯ SHDN = 3V. Symbol Parameter Conditions Input Voltage Range Min Typ 2.5 Max Units 7 V IQ Quiescent Current VFB = 0.2 V 0.5 0.7 mA ISD Shutdown Current VSHDN = 0 V 0.05 1 µA VFB FB Pin Voltage 4 LEDs at 15 mA 95 105 mV IFB FB Pin Leakage Current 1 2 µA Shutdown High Threshold 85 0.85 V Shutdown Low Threshold ISHDN Shutdown Pin Current 0.25 V 1 nA 1.6 MHz fSW Boost Converter Frequency 0.8 1.2 DC Maximum Switch Duty Cycle 90 95 ISWL Switch Current Limit 400 550 780 mA % Switch Saturation Voltage ISW = 300 mA 150 200 mV Switch Leakage Current Switch Off, VSW = 5 V 0.01 5 µA Efficiency Figure 1 with specified components 83 % Notes: (1) These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may affect device reliability. All voltages are with respect to ground. © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 3 Doc. No. MD-5005 Rev. T CAT37 TYPICAL CHARACTERISTICS VIN = 3.6V, TAMB = 25ºC, CIN = 4.7µF, COUT = 1µF, L = 6.8µH, unless otherwise specified. LED Current vs. Temperature LED Current vs. Input Voltage 30 16.0 LEDs 3 3LEDs LED CURRENT [mA] LED CURRENT [mA] 20mA 20mA 20 10mA 10mA 10 15.5 15.0 4 4LEDs LEDs 14.5 14.0 0 2 3 4 5 6 -50 -25 0 25 50 75 100 TEMPERATURE [ºC] INPUT VOLTAGE [V] FB Pin Voltage vs. LED Current FB Pin Voltage vs. Temperature 100 110 FB PIN VOLTAGE [mV] FB PIN VOLTAGE [mV] 105 3 LEDs 3 LEDs 100 95 90 85 95 90 85 4 LEDs at at 15mA 15mA 4LEDs VIN = 3.6V VIN = 3.6V 80 80 0 5 10 LED CURRENT [mA] 15 -50 20 25 50 75 100 Switching Frequency vs. Temperature 1.3 1.3 SWITCHING FREQUENCY [MHz] SWITCH FREQUENCY [MHz] 0 TEMPERATURE [ºC] Switching Frequency vs. Input Voltage 1.2 1.1 1.0 0.9 4 LEDs 4 LEDs 0.8 -25 1.2 1.1 LOAD = 20mA LOAD =20 mA 1.0 LOAD LOAD==33LEDs LEDsVIN =VIN 3.6V = 3.6V 0.9 0.8 1 2 3 4 5 6 -50 INPUT VOLTAGE [V] Doc. No. MD-5005 Rev. T 4 -25 0 25 50 TEMPERATURE [ºC] 75 100 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT37 TYPICAL CHARACTERISTICS VIN = 3.6V, TAMB = 25ºC , CIN = 4.7µF, COUT = 1µF, L = 6.8µH, unless otherwise specified. Efficiency vs. Input Voltage Efficiency vs. Temperature 90 86 85 84 80 82 EFFICIENCY [%] EFFICIENCY [%] LOAD = 20 mA 33 LEDS LEDsatat15mA 15mA VOUT == 10V VOUT 10V 75 70 65 LOAD = 15 mA LOAD = 10 mA 80 78 LOAD = 3 LEDs = VIN 3.6V= 3.6V 76 60 74 2 3 4 5 6 -50 INPUT VOLTAGE [V] VSW, IL, & VOUT Waveforms -25 0 25 50 TEMPERATURE [ºC] 75 100 PWM on SHDN ¯¯¯¯¯ pin at 1kHz Enable Power-Up Waveforms © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 5 Doc. No. MD-5005 Rev. T CAT37 OPERATION The CAT37 device is a high efficiency, constant frequency, current regulating boost driver for white LEDs. While maintaining LED current regulation, the CAT37 boost converter automatically adjusts the FB pin voltage to be as low as possible. A low FB pin voltage ensures high efficiency. The device includes a switch and an internally compensated loop for the regulation of the current in the LEDs. 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. Operation can be best understood by examining the block diagram. The FB pin is regulated at 95mV and the current through the external resistor will set the regulated current in the LEDs at: ILED = PWM dimming operation can be achieved by switching the ¯¯¯¯¯ SHDN pin or by pulling the FB pin higher than 95mV. 0.095 R1 BLOCK DIAGRAM D1 L1 VIN 5 C1 1 VIN 4 C2 SW SHDN 1.2MHz Oscillator Over Voltage Protection (22V) 90kΩ 6kΩ PWM & Logic ILED FB 3 Error Amp R1 0.095V REF Current Sense Amp CAT37 GND 2 Figure 2. CAT37 Block Diagram Doc. No. MD-5005 Rev. T 6 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT37 APPLICATION INFORMATION CAPACITOR SELECTION Table 2: Schottky Diode Suppliers 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 1.0µF output capacitor is recommended for most applications. Part MBR0520 MBR0530 MBR0540 ZHCS400 Table 4: R1 Resistor Values www.t-yuden.com Murata www.murata.com Kemet www.kemet.com AVX www.avxcorp.com For other LED current values, use the following equation to choose R1. R1 = DIODE SELECTION Characteristics subject to change without notice 0.095 ILED Most white LEDs are driven at maximum currents of 15mA to 20mA. Some higher power designs will use two parallel strings of LEDs for greater light output, resulting in 30mA to 40mA (two strings of 15mA to 20mA) flowing through the R1 resistor. Schottky diodes, with their low forward voltage drop and fast switching speed, are the ideal choice for high efficiency applications. Table 2 shows several different Schottky diodes that work well with the CAT37. 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 0.4A or 0.5A diode will be sufficient for most designs. © Catalyst Semiconductor, Inc. R1 (Ω) 2.37 3.16 4.75 6.34 7.87 9.53 19.1 ILED (mA) 40 30 25 20 15 10 5 Table 1: Ceramic Capacitor Manufacturers Taiyo Yuden Zetex The LED current is programmed with a single resistor connected to the FB pin. The FB pin is internally regulated to 95 mV, which sets the current flowing through R1 and the LEDs as equal to 0.095/R1. For the best accuracy, a 1% or better resistor is recommended. Table 3 shows several typical 1% R1 values. Low profile ceramic capacitors with a 1mm 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 CAT37. A 1µF or 4.7µF input capacitor is recommended. Table 1 shows a list of several ceramic capacitor manufacturers. Consult the manufacturers for detailed information as new products and package options are introduced regularly. Web ON Semiconductor www.onsemi.com 800.282.9855 LED CURRENT PROGRAMMING The voltage rating of the output capacitor C2 depends on the number of LEDs driven in the series. A 16V ceramic capacitor is recommended when driving 3 or 4 LEDs. Supplier Supplier 7 Doc. No. MD-5005 Rev. T CAT37 LED DIMMING WITH DC SIGNAL LED DIMMING WITH A LOGIC SIGNAL Dimming the LEDs can be done by applying a variable DC voltage as shown on Figure 3. As the VDC increase the voltage across R1 decreases and therefore lower the LED current. The resistors R2 and R3 must be large enough so that their current (tens of µA) is much smaller than the LED current but much larger than the FB leakage current (IFB). When adjusting VDC between 0V and 2V, the resistors shown on Figure 3 will set the LED current between 0mA and 15mA. For applications that need to adjust the LED brightness in discrete steps, a logic signal can be used as shown in Figure 5. R1 sets the minimum LED current value (when the NMOS switch is OFF): R1 = RINCR determines how much LED current increases when the external NMOS switch is turned ON. 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 5kHz to 40kHz PWM signal is used. RINCR = The SW pin, schottky diode and capacitor C2 signal path should be kept as short as possible. The ground connection for the R1 resistor should be tied directly to the GND pin and not be shared with other components. CAT37 CAT37 FB FB FB R2 1kΩ VDC PWM R1 6.3Ω Figure 3. Dimming with a DC Voltage Doc. No. MD-5005 Rev. T 10kΩ ILED(INCREASE ) The CAT37 is a high-frequency switching regulator where proper PCB board layout and component placement can minimize noise and radiation and increase efficiency. To maximize efficiency, the CAT37 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. 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 15mA or 20mA. 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. R3 18kΩ 0.095 V PCB LAYOUT GUIDELINES A filtered PWM signal is used to dim the LEDs, as shown in Figure 4. CAT37 0.095 V ILED(MIN) R3 18kΩ R2 1kΩ 0.1µF Figure 4. Dimming with a Filtered PWM Signal 8 RINCR R1 6.3Ω Logic Signal 2N7002 R1 6.3Ω Figure 5. Dimming with a Logic Signal © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT37 TYPICAL APPLICATION CIRCUITS Efficiency – Two LEDs Two LEDs with DC Level Dimming Control L1 6.8µH D1 VIN 3V to 4.2V 90 VDC Dimming 5 VIN 1 SW 18k 15mA CAT37 4 C2 1µF EFFICIENCY [%] C1 1µF FB SHDN 1k 3 VIN==3.6V 3.6V VIN 85 VIN == 3.0V 3.0V VIN 80 75 70 65 60 GND 2 0 R1 6.34kΩ 10 15 20 25 30 LED CURRENT [mA] Efficiency –- Three LEDs Three LEDs with DC Level Dimming Control L1 6.8µH 5 D1 VIN 3V to 4.2V 90 5 VIN 1 SW 18k 15mA CAT37 4 C2 1µF FB SHDN 3 1k VIN = 3.6V VIN=3.6V 85 EFFICIENCY [%] VDC Dimming C1 1µF 80 VIN =VIN=3.0V 3.0V 75 70 65 60 GND 2 R1 6.34kΩ 0 D1 0.1µF 18k CAT37 4 FB SHDN GND 2 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice C2 1µF 15mA 3 EFFICIENCY [%] 85 10k 1 SW 20 25 30 90 PWM 5 VIN 15 Efficiency – Four LEDs VIN 3V to 4.2V C1 1µF 10 LED CURRENT [mA] Four LEDs with PWM Dimming Control L1 6.8µH 5 VIN = 3.6V VIN=3.6V 80 VIN=3.0V VIN = 3.0V 75 70 65 60 1k 0 R1 6.34kΩ 9 5 10 15 20 LED CURRENT [mA] 25 30 Doc. No. MD-5005 Rev. T CAT37 PACKAGE OUTLINE DRAWING TSOT-23 5-Lead (TD) (1)(2) SYMBOL D MIN NOM MAX A1 0.01 0.05 0.10 A2 0.80 0.87 0.90 b 0.30 c 0.12 A e E1 E 1.00 0.45 0.15 D 2.90 BSC E 2.80 BSC E1 1.60 BSC e 0.95 TYP L 0.30 0.40 L1 0.60 REF L2 0.25 BSC θ 0º 0.20 0.50 8º TOP VIEW A2 A b θ L A1 c L1 SIDE VIEW L2 END VIEW For current Tape and Reel information, download the PDF file from: http://www.catsemi.com/documents/TapeandReel.pdf Notes: (1) All dimensions are in millimeters. Angles in degrees. (2) Complies with JEDEC standard MO-193. Doc. No. MD-5005 Rev. T 10 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT37 EXAMPLE OF ORDERING INFORMATION 1 Prefix Device # CAT 37 Suffix TD Product Number 37 Optional Company ID I –G Industrial Temperature I: Range -40ºC to + 85ºC Package TD: TSOT-23 T3 Tape & Reel T: Tape & Reel 3: 3,000/Reel Lead Finish Blank: Matte-Tin G: NiPdAu Notes: (1) All packages are RoHS-compliant (Lead-free, Halogen-free). (2) The standard lead finish is NiPdAu. (3) The device used in the above example is a CAT37TDI-GT3 (TSOT-23, NiPdAu, Tape & Reel, 3,000/Reel). (4) For additional package and temperature options, please contact your nearest Catalyst Semiconductor Sales office. © 2005 Catalyst Semiconductor, Inc. Characteristics subject to change without notice 11 Doc. No. 5014 Rev. A CAT37 REVISION HISTORY Date Rev. 25-Sept-03 H 25-Sept-03 I Reason Updated Ordering Information - part numers Changed L1 for each figure from 22µH to 6.8µH Changed VIN for Typical Application from 2.7V to 4.2V to 3V to 5V Changed C1 for each typical application circuit from 4.7µF to 1µF Changed C2 for each typical application circuit from 2.2µF to 1µF Changed VIN for each for each typical application circuit from 1.8V to 3V to 3V to 4.2V Updated Ordering Information - part numbers Updated Features Changed R1 for Typical Application figure and Typical Application Circuit figures from 6.34Ω to 6.8Ω Updated Description (2V to 2.5V input supply voltage) Updated Ordering Information (added package marking code) Updated Electrical Specifications Updated Table 4 (R1 Resistor Value) with new values Updated LED dimming with logic signal (0.095V to 0.105V) Updated Typical Application figures Updated Electrical Specifications Updated Operation text Updated LED current programming text Updated Table 4 (R1 Resistor Value) with new values Updated LED dimming equations Updated Typical Application Circuit figures 6-Nov-03 J 8-Dec-03 K 10-Dec-03 L 18-Dec-03 M 22-Dec-03 N 9-June-04 O Updated FB Pin Leakage Current in Electrical Specifications Added Typical Characteristics graphs (pages 4-6) Added Efficiency graphs to Typical Application Circuits Changed package drawing for 5-lead SOT-23 Updated Absolute Maximum Ratings Deleted temp range from Electrical Specifications Added Recommended Operating Conditions Updated Block Diagram Updated Electrical Specifications (changed VRSET to VFB in IQ) 15-June-04 P Reoved Preliminary data sheet designation 22-Sept-04 Q Added Green Packages in all areas 1-Nov-04 R Eliminated TDFN (3 x 4.9mm) package Updated Ordering Information 07-July-05 S 19-May-08 T Doc. No. MD-5005 Rev. T Update Features Update Description Update Ordering Information Update Pin Configuration Update Pin Description Update Block Diagram Update Package Outlines Add TSOT-23 in NiPdAu plated finish Add Example of Ordering Information Update Package Outline Drawing Add MD- to document number 12 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice Copyrights, Trademarks and Patents © Catalyst Semiconductor, Inc. Trademarks and registered trademarks of Catalyst Semiconductor include each of the following: Adaptive Analog™, Beyond Memory™, DPP™, EZDim™, LDD™, MiniPot™, Quad-Mode™ and Quantum Charge Programmable™ Catalyst Semiconductor has been issued U.S. and foreign patents and has patent applications pending that protect its products. CATALYST SEMICONDUCTOR MAKES NO WARRANTY, REPRESENTATION OR GUARANTEE, EXPRESS OR IMPLIED, REGARDING THE SUITABILITY OF ITS PRODUCTS FOR ANY PARTICULAR PURPOSE, NOR THAT THE USE OF ITS PRODUCTS WILL NOT INFRINGE ITS INTELLECTUAL PROPERTY RIGHTS OR THE RIGHTS OF THIRD PARTIES WITH RESPECT TO ANY PARTICULAR USE OR APPLICATION AND SPECIFICALLY DISCLAIMS ANY AND ALL LIABILITY ARISING OUT OF ANY SUCH USE OR APPLICATION, INCLUDING BUT NOT LIMITED TO, CONSEQUENTIAL OR INCIDENTAL DAMAGES. Catalyst Semiconductor products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the Catalyst Semiconductor product could create a situation where personal injury or death may occur. Catalyst Semiconductor reserves the right to make changes to or discontinue any product or service described herein without notice. Products with data sheets labeled "Advance Information" or "Preliminary" and other products described herein may not be in production or offered for sale. Catalyst Semiconductor advises customers to obtain the current version of the relevant product information before placing orders. Circuit diagrams illustrate typical semiconductor applications and may not be complete. Catalyst Semiconductor, Inc. Corporate Headquarters 2975 Stender Way Santa Clara, CA 95054 Phone: 408.542.1000 Fax: 408.542.1200 0Hwww.catsemi.com Document No: MD-5005 Revision: T Issue date: 05/19/2008