H CAT37 EE GEN FR ALO CMOS White LED Driver Boost Converter LE FEATURES A D F R E ETM ■ Low quiescent ground current (0.5mA typical) ■ Drives up to 4 White LEDs in series ■ Power efficiency over 80% ■ Shutdown current less than 1µA ■ Compatible pinout with LT1937 ■ Load fault protection against open-circuits ■ Adjustable output current (up to 40mA) ■ Low value external components ■ High frequency 1.2MHz operation ■ Low profile 5-lead SOT23 (1mm max) and TDFN (0.8mm) package ■ Input voltage operation down to 2.5V Ω) power switch ■ Low resistance (0.5Ω APPLICATIONS ■ Color LCD and keypad backlighting ■ Digital cameras ■ Cellular phones ■ PDAs/Games ■ Handheld terminals ■ Portable MP3 players DESCRIPTION A high voltage output stage allows up to 4 White LEDs to be driven in series. Series drive provides inherent current matching. 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. 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. 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 batterypowered applications. 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 (1mm max height) 5-lead thin SOT23 package and in a TDFN (0.8mm max height) package. TYPICAL APPLICATION D1 VIN 3 V to 5 V 5 VIN 1 SW CAT37 OFF ON 4 15mA FB SHDN 3 GND 2 C1: Taiyo Yuden JMK212BJ475 C2: Taiyo Yuden EMK212BJ105 D1: Zetez ZHCS400 L1: Panasonic ELJEA6R8 or equivalent SOT23 Pin Numbers Figure 1. Driver for Four High-Brightness White LEDs © 2004 by Catalyst Semiconductor, Inc. Characteristics subject to change without notice 1 Doc No. 5005, Rev. R CAT37 ORDERING INFORMATION Part Number Package Tube Quantity Reel Quantity Package Marking Code CAT37EKK-TE7 5-lead, thin SOT23 — 3000 BF CAT37RD4-TE13 8-pad TDFN (3x3mm) 120 TBD CCEW CAT37TDI 5-lead, thin SOT23 Lead Free — — LM PIN CONFIGURATION SW 1 GND 2 FB 3 VIN 5 CAT37 SHDN 4 5-Lead SOT-23 1mm maximum height Power GND 1 8 SW VIN 2 7 NC NC 3 6 FB SHDN 4 5 GND (Top View) TDFN Package: 3mm x 3mm 0.8mm maximum height (RD4) θ [Free Air] PIN DESCRIPTIONS Pin Number SOT23 Pin Number TDFN Name 1 8 SW 2 5 GND 3 6 FB 4 4 SHDN 5 2 VIN — 1 Power Ground Doc. No. 5005, Rev. R 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. 2 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. Power Ground CAT37 ABSOLUTE MAXIMUM RATINGS VIN , FB, SHDN Voltage ......................................... 8 V Storage Temperature .......................... -65°C to 160°C SW Voltage .......................................................... 20 V ESD Rating - Human Body Model .................... 2000V Junction Temperature ....................................... 125°C Lead Soldering Temperature ............................ 300°C RECOMMENDED OPERATING CONDITIONS Parameter Range Unit VIN 2.5 to 7 V Ambient Temperature Range -40 to +85 ° C Inductor L1 6.8 ±20% typical µH Input Capacitor C1 1.0 ±20% typical µF Output Capacitor C2 1.0 ±20% typical µF ILED with 1 to 4 LEDs in series 0 to 20 mA ELECTRICAL SPECIFICATIONS Over recommended operating conditions unless otherwise specified. TA = 25˚C, VIN = 3V and VSHDN = 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 95 105 mV IFB FB Pin Leakage Current 1 2 µA 4 LEDs at 15 mA 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 90 95 400 550 780 mA ISW = 300 mA 150 200 mV Switch Off, VSW = 5 V 0.01 5 µA Figure 1 with 83 % Duty Cycle ISWL Switch Current Limit Switch Saturation Voltage Switch Leakage Current Efficiency % specified components 3 Doc No. 5005, Rev. R CAT37 TYPICAL CHARACTERISTICS VIN = 3.6 V,TAMB = 25˚C, CIN = 4.7 µF, COUT = 1µF, L = 6.8 µH, unless otherwise specified. LED Current vs. Temperature LED Current vs. Input Voltage 16.0 30 LED CURRENT [mA] LED CURRENT [mA] LEDs 33LEDs 20mA 20mA 20 10mA 10mA 10 15.5 15.0 4 4LEDs LEDs 14.5 14.0 0 2 3 4 5 -50 6 -25 0 25 50 75 100 INPUT VOLTAGE [V] FB Pin Voltage vs. LED Current FB Pin Voltage vs. Temperature 100 105 FB PIN VOLTAGE [mV] FB PIN VOLTAGE [mV] 110 LEDs 33 LEDs 100 95 90 85 5 10 15 LED CURRENT [mA] 90 85 80 -50 80 0 95 20 Switching Frequency vs. Input Voltage SWITCHING FREQUENCY [MHz] SWITCH FREQUENCY [MHz] 1.2 1.1 1.0 0.9 4 LEDs 4 LEDs 1 2 3 4 5 6 0 25 50 75 100 1.3 1.2 1.1 LOAD = mA 20mA LOAD =20 1.0 LOAD VIN LOAD= =3 LEDs 3 LEDs =VIN 3.6V= 3.6V 0.9 0.8 -50 INPUT VOLTAGE [V] Doc. No. 5005, Rev. R -25 Switching Frequency vs. Temperature 1.3 0.8 4 LEDs at 4LEDs at15mA 15mA VIN = 3.6V VIN = 3.6V 4 -25 0 25 50 75 100 CAT37 TYPICAL CHARACTERISTICS VIN = 3.6 V,TAMB = 25˚C, CIN = 4.7 µF, COUT = 1µF, L = 6.8 µH, unless otherwise specified. Efficiency vs. Input Voltage Efficiency vs. Temperature 86 90 84 EFFICIENCY [%] 85 EFFICIENCY [%] LOAD = 20 mA LOAD =20 mA 80 33 LEDS at at 15mA LEDs 15mA VOUT = 10V 75 VOUT = 10V 70 65 82 LOAD 15 mA LOAD =15= mA 80 LOAD = mA 10 mA LOAD =10 78 LOAD =3=LEDs VIN LOAD 3 LEDs = 3.6V 76 60 VIN = 3.6V 74 2 3 4 5 INPUT VOLTAGE [V] 6 -50 -25 0 25 50 TEMPERATURE [ºC] 75 100 PWM on SHDN pin at 1kHz VSW, IL, & VOUT Waveforms Enable Power-Up Waveforms 5 Doc No. 5005, Rev. R CAT37 OPERATION 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 CAT37 device is a high efficiency, constant frequency, current regulating boost driver for white LEDs. 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 95 mV and the current through the external resistor will set the regulated current in the LEDs at: PWM dimming operation can be achieved by switching the SHDN pin or by pulling the FB pin higher than 95mV. ILED = 0.095/R1 BLOCK DIAGRAM L1 VIN C1 4 D1 5 1 VIN SW C2 1.2 MHz Clock SHDN Over Voltage Protection (22V) CAT37 Error Amp 0.095V REF + Current Sense Amp GND 2 Note: SOT23 Pin Numbers Figure 2. CAT37 Block Diagram Doc. No. 5005, Rev. R FB 3 + - PWM & Logic 6 ILED R1 CAT37 APPLICATION INFORMATION Table 2. Schottky Diode Suppliers CAPACITOR SELECTION Part Supplier 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. MBR0520 ON Semiconductor MBR0530 www.onsemi.com MBR0540 800.282.9855 ZHCS400 Zetex LED CURRENT PROGRAMMING 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. The voltage rating of the output capacitor C2 depends on the number of LEDs driven in the series. A 16 V ceramic capacitor is recommended when driving 3 or 4 LEDs. 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 1 µF or 4.7 µF 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. Table 3. R1 Resistor Values Table 1. Ceramic Capacitor Manufacturers Supplier Web Taiyo Yuden www.t-yuden.com Murata www.murata.com Kemet www.kemet.com AVX www.avxcorp.com ILED (mA) R1 (Ω) 40 30 20 15 12 10 5 2.37 3.16 4.75 6.34 7.87 9.53 19.1 For other LED current values, use the following equation to choose R1. DIODE SELECTION R1= 0.095 ILED 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 onethird the time), so a 0.4A or 0.5A diode will be sufficient for most designs. 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. 7 Doc No. 5005, Rev. R 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= 0.095V ILED(MIN) RINCR determines how much LED current increases when the external NMOS switch is turned ON. LED DIMMING WITH PWM SIGNAL RINCR= 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. PCB LAYOUT GUIDELINES 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. A filtered PWM signal is used to dim the LEDs, as shown in Figure 4. 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. VDC 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 R3 18k R2 1k 10k PWM 0.095V ILED(INCREASE) CAT37 FB R3 18k R2 1k RINCR LOGIC SIGNAL Figure 3. Dimming with a DC Voltage Doc. No. 5005, Rev. R Figure 4. Dimming with a Filtered PWM Signal 8 2N7002 R1 Figure 5. Dimming with a Logic Signal CAT37 TYPICAL APPLICATION CIRCUITS The application diagrams are shown for the SOT23 pin numbers. Two LEDs with DC Level Dimming Control Efficiency - Two LEDs D1 90 VIN 3 V to 4.2 V VIN = 3.6V VIN 3.6V 85 1 SW 18k CAT37 4 FB SHDN VDC Dimming 1k 3 EFFICIENCY [%] 5 VIN 15mA GND 2 VIN = VIN = 3.0V 3.0V 80 75 70 65 60 0 5 10 15 20 25 LED CURRENT [mA] 30 Efficiency - Three LEDs Three LEDs with DC Level Dimming Control D1 VIN 3 V to 4.2 V 90 1 SW 18k CAT37 4 FB SHDN 1k 3 VIN = 3.6V VIN=3.6V 85 VDC Dimming 15mA GND 2 EFFICIENCY [%] 5 VIN 80 VIN =VIN=3.0V 3.0V 75 70 65 60 0 Four LEDs with PWM Dimming Control 5 10 15 20 25 LED CURRENT [mA] 30 Efficiency - Four LEDs D1 VIN 3 V to 4.2 V 90 PWM SW 18k CAT37 SHDN FB 3 1k 15mA EFFICIENCY [%] 1 10k 5 VIN 4 85 VIN = 3.6V VIN=3.6V 80 VIN=3.0V VIN = 3.0V 75 70 65 GND 2 60 0 5 10 15 20 25 30 LED CURRENT [mA] 9 Doc No. 5005, Rev. R CAT37 PACKAGE OUTLINES 5-LEAD SOT-23 ALL DIMENSIONS IN MILLIMETERS 0.95 REF 0.50 MAX 0.35 MIN PIN 1 3.00 MAX 2.60 MIN 1.90 REF 3.00 MAX 2.80 MIN 1.75 MAX 1.50 MIN 0.20 MAX 0.09 MIN 0.90 MAX 0.80 MIN 1.00 MAX 0.20 GAUGE PLANE 0.15 MAX 0.00 MIN 0.70 MAX 0.50 MIN 0.60 MAX 0.10 MIN Doc. No. 5005, Rev. R 10 CAT37 TDFN 3X3 MM PACKAGE (RD4) 5 0.75 + 0.05 A B 3.00 + 0.10 (S) 8 2X 1 4 0.15 C 2X 3.00 + 0.10 (S) 0.0 - 0.05 0.15 C PIN 1 INDEX AREA 5 8 1.50 + 0.10 0.75 + 0.05 C 2.30 + 0.10 C0.35 0.25 min. PIN 1 ID 1 0.30 + 0.07 (8x) 0.30 + 0.10 (8x) 0.65 TYP. (6x) 1.95 REF. (2x) NOTE: 1. ALL DIMENSION ARE IN mm. ANGLES IN DEGREES. 2. COPLANARITY SHALL NOT EXCEED 0.08 mm. 3. WARPAGE SHALL NOT EXCEED 0.10 mm. 4. PACKAGE LENGTH / PACKAGE WIDTH ARE CONSIDERED AS SPECIAL CHARACTERISTIC(S) 5. REFER JEDEC MO-229 / WEEC 11 Doc No. 5005, Rev. R CAT37 REVISION HISTORY Date Rev. Reason 9/25/2003 H Updated Ordering Information - part numers Changed L1 for each figure from 22 µH to 6.8 µH Changed VIN for Typical Application from 2.7V to 4.2 Vto 3V to 5V Changed C1 for each typical application circuit from 4.7 µF to 1 µF Changed C2 for each typical application circuit from 2.2 µF to 1 µF Changed VIN for each for each typical application circuit from 1.8 V to 3 V to 3 V to 4.2 V 9/25/2003 I Updated Ordering Information - part numbers 11/6/2003 J 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) 12/8/2003 K 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 12/10/2003 L 12/18/2003 M 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 12/22/2003 N Updated Absolute Maximum Ratings Deleted temp range from Electrical Specifications Added Recommended Operating Conditions Updated Block Diagram 6/9/2004 O Updated Electrical Specifications (changed VRSET to VFB in IQ 6/15/2004 P Reoved Preliminary data sheet designation 9/22/2004 Q Added Green Packages in all areas 11/1/2004 R Eliminated TDFN (3x4.9mm) package Updated Ordering Information Doc. No. 5005, Rev. R 12 CAT37 Copyrights, Trademarks and Patents Trademarks and registered trademarks of Catalyst Semiconductor include each of the following: DPP ™ AE2 ™ Catalyst Semiconductor has been issued U.S. and foreign patents and has patent applications pending that protect its products. For a complete list of patents issued to Catalyst Semiconductor contact the Company’s corporate office at 408.542.1000. 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 1250 Borregas Avenue Sunnyvale, CA 94089 Phone: 408.542.1000 Fax: 408.542.1200 www.catalyst-semiconductor.com Publication #: Revison: Issue date: 13 5005 R 11/1/04 Doc No. 5005, Rev. R