CAT4240 6 Watt Boost LED Driver FEATURES DESCRIPTION Switch Current Limit 750mA Drives High Voltage LED strings (38V) Up to 94% Efficiency Low Quiescent Ground Current 0.6mA 1MHz Fixed Frequency Low noise Operation Soft start “in-rush” current limiting Shutdown current less than 1μA Open LED Overvoltage Protection Automatic Shutdown at 1.9V (UVLO) Thermal overload protection Thin SOT23 5-Lead (1mm max height) APPLICATIONS The CAT4240 is a DC/DC step-up converter that delivers an accurate constant current ideal for driving LEDs. Operation at a fixed switching frequency of 1MHz allows the device to be used with small value external ceramic capacitors and inductor. LEDs connected in series are driven with a regulated current set by the external resistor R1. The CAT4240 high-voltage output stage is perfect for driving mid-size and large panel displays containing up to ten white LEDs in series. 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 “zero” quiescent current. In addition to thermal protection and overload current limiting, the device also enters a very low power operating mode during “Open LED” fault conditions. The device is housed in a low profile (1mm max height) 5-lead thin SOT23 package for space critical applications. GPS Navigation Systems Portable Media Players Handheld Devices, Digital Cameras ORDERING INFORMATION Part Number Package CAT4240TD-GT3 TSOT23-5 Green* Quantity Package per Reel Marking 3000 TG * NiPdAu Plated Finish For Ordering Information details, see page 13. Typical Application Circuit Pin Configuration SW GND FB 1 5 L1 VL TSOT23 5-Lead (1mm max height) 8V to 16V VIN VIN 5V 2 C1 C3 1µF 3 4 SHDN D1 47µH 4.7µF/16V C2 SW VIN CAT4240 SHDN VOUT FB GND 1µF/50V 300mA (300mV) R2 1kΩ R1 1Ω Top View L1: Sumida CDRH6D28-470 D1: Central CMSH1-40 (rated 40V) © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 1 Doc. No. MD-5026 Rev. C CAT4240 ABSOLUTE MAXIMUM RATINGS Parameters VIN, FB voltage ¯¯¯¯¯ voltage SHDN SW voltage Storage Temperature Range Junction Temperature Range Lead Temperature Ratings -0.3 to +7 -0.3 to +7 -0.3 to 60 -65 to +160 -40 to +150 300 Units V V V ºC ºC ºC RECOMMENDED OPERATING CONDITIONS Typical application circuit with external components are shown on page 1. Parameters VIN SW pin voltage Ambient Temperature Range (1) Range up to 5.5 0 to 38 -40 to +85 Units V V ºC DC ELECTRICAL CHARACTERISTICS VIN = 3.6V, ambient temperature of 25ºC (over recommended operating conditions unless specified otherwise). Symbol Parameter IQ Operating Current ISD VFB IFB ILED Shutdown Current FB Pin Voltage FB pin input leakage Programmed LED Current Test Conditions VFB = 0.2V VFB = 0.4V (not switching) VSHDN ¯¯¯¯¯ = 0V 6 LEDs with ILED = 75mA R1 = 10Ω R1 = 5Ω Enable Threshold Level Shutdown Threshold Level VIH VIL FSW DC ¯¯¯¯¯ Logic High SHDN ¯¯¯¯¯ Logic Low SHDN Switching Frequency Maximum Duty Cycle ILIM Switch Current Limit VIN = 3.6V VIN = 5V RSW Switch “On” Resistance ISW = 100mA ILEAK Switch Leakage Current Switch Off, VSW = 30V Min 285 28.5 Typ 0.6 0.1 Max 1.5 0.6 Units mA 0.1 300 1 315 1 31.5 µA mV µA mA 1.5 V V MHz % 30 60 0.8 0.7 1.0 92 0.4 0.8 VIN = 3V 1.3 600 750 mA 1.0 2.0 Ω 2 5 µA Thermal Shutdown 150 ºC Thermal Hysteresis 20 ºC VUVLO Undervoltage Lockout (UVLO) Threshold 1.9 V VOV-SW Overvoltage Detection Threshold 40 V 42 V VOCL Output Voltage Clamp “Open LED” Note: (1) Thin SOT23-5 package thermal resistance θJA = 135°C/W when mounted on board over a ground plane. Doc. No. MD-5026 Rev. C 2 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4240 TYPICAL CHARACTERISTICS VIN = 5V, VL = 13V, TAMB = 25ºC, typical application circuit unless otherwise specified. Quiescent Current vs. VIN (Switching) 2.0 200 QUIESCENT CURRENT [mA] QUIESCENT CURRENT [μA] . Quiescent Current vs. VIN (Not Switching) VFB = 0.4V 150 100 1.5 1.0 0.5 0.0 50 3.0 3.5 4.0 4.5 5.0 3.0 5.5 FB pin voltage vs. Temperature 4.5 5.0 5.5 FB Pin Voltage vs. Output Current 310 FB PIN VOLTAGE [mV] 303 FB PIN VOLTAGE [mV] 4.0 INPUT VOLTAGE [V] INPUT VOLTAGE [V] 302 301 300 299 298 297 305 300 295 4 LEDs 290 -50 0 50 100 150 0 TEMPERATURE [ºC] 50 100 150 200 OUTPUT CURRENT [mA] Switching Frequency vs. Supply Voltage Switch ON Resistance vs. Input Voltage 2.0 1.2 SWITCH RESISTANCE [Ω] SWITCHING FREQUENCY [MHz] 3.5 1.1 1.0 0.9 1.5 1.0 0.5 0.0 0.8 3.0 3.5 4.0 4.5 5.0 3.0 5.5 4.0 4.5 5.0 5.5 INPUT VOLTAGE [V] INPUT VOLTAGE [V] © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 3.5 3 Doc. No. MD-5026 Rev. C CAT4240 TYPICAL CHARACTERISTICS VIN = 5V, VL = 13V, TAMB = 25ºC, typical application circuit unless otherwise specified. LED Current vs. Input Voltage LED CURRENT VARIATION [%] . LED CURRENT [mA] 350 LED Current Regulation RSET = 1Ω VOUT = 19.5V 300 250 200 RSET = 2Ω VOUT = 18.8V 150 100 8 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 8 9 10 11 12 13 14 15 16 INDUCTOR VOLTAGE [V] Efficiency vs. Inductor Voltage (6 LEDs) 100 95 95 EFFICIENCY [%] 100 90 85 80 90 85 80 50 100 150 200 250 LED CURRENT [mA] 300 8 Power-up with 6 LEDs at 300mA Doc. No. MD-5026 Rev. C 6 LEDs @ 150mA -2.0 9 10 11 12 13 14 15 16 INDUCTOR VOLTAGE [V] Efficiency vs. Load Current (6 LEDs) EFFICIENCY [%] 2.0 9 10 11 12 13 14 15 16 INDUCTOR VOLTAGE [V] Switching Waveform 4 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4240 TYPICAL CHARACTERISTICS VIN = 5V, VL = 13V, TAMB = 25ºC, typical application circuit unless otherwise specified. Maximum Output Current Shutdown Voltage 1.0 400 SHUTDOWN VOLTAGE [V] MAX OUTPUT CURRENT [mA] 500 VOUT = 20V 300 VOUT = 30V 200 -40°C -25°C 0.8 0.6 125°C 0.4 85°C 0.2 100 8 3.0 9 10 11 12 13 14 15 16 INDUCTOR VOLTAGE [V] 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V] Switch Current Limit SW CURRENT LIMIT [mA] 1200 1100 1000 900 800 VOUT = 20V 700 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE [V] © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 5.5 5 Doc. No. MD-5026 Rev. C CAT4240 PIN DESCRIPTION VIN is the supply input for the internal logic. The device is compatible with supply voltages down to 2.8V and up to 5.5V. It is recommended that a small bypass ceramic capacitor (4.7μF) be placed between the VIN and GND pins near the device. If the supply voltage drops below 1.9V, the device stops switching. SW pin is connected to the drain of the internal CMOS power switch of the boost converter. The inductor and the Schottky diode anode should be connected to the SW pin. Traces going to the SW pin should be as short as possible with minimum loop area. An overvoltage detection circuit is connected to the SW pin. When the voltage reaches 40V, the device enters a low power operating mode preventing the SW voltage from exceeding the maximum rating. ¯¯¯¯¯ is the shutdown logic input. When the pin is SHDN tied to a voltage lower than 0.4V, the device is in shutdown mode, drawing nearly zero current. When the pin is connected to a voltage higher than 1.5V, the device is enabled. FB feedback pin is regulated at 0.3V. A resistor connected between the FB pin and ground sets the LED current according to the formula: GND is the ground reference pin. This pin should be connected directly to the ground plane on the PCB. ILED = 0.3V/R1 The lower LED cathode is connected to the FB pin. Pin # Name 1 2 3 4 5 SW GND FB ¯¯¯¯¯ SHDN VIN Function Switch pin. This is the drain of the internal power switch. Ground pin. Connect the pin to the ground plane. Feedback pin. Connect to the last LED cathode. Shutdown pin (Logic Low). Set high to enable the driver. Power Supply input. SIMPLIFIED BLOCK DIAGRAM VOUT VIN SW C2 C1 1MHz Oscillator Ref 300mV Over Voltage Protection – + PWM & Logic + – LED Current RS GND Current Sense – SHDN Thermal Shutdown & UVLO + VIN Driver FB R1 Doc. No. MD-5026 Rev. C 6 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4240 DEVICE OPERATION The CAT4240 is a fixed frequency (1MHz), low noise, inductive boost converter that provides a constant current with excellent line and load regulation. The device uses a high-voltage CMOS power switch between the SW pin and ground to energize the inductor. When the switch is turned off, the stored energy in the inductor is released into the load via the Schottky diode. When the inductor is connected to a 9V supply or higher, the CAT4240 can drive 6 LEDs in series at 300mA delivering a total power of 6 Watts into the load. A separate 5V supply voltage is connected to the VIN pin. In the event of an “Open LED” fault condition, where the feedback control loop becomes open, the output voltage will continue to increase. Once this voltage exceeds 40V, an internal protection circuit will become active and place the device into a very low power safe operating mode. The on/off duty cycle of the power switch is internally adjusted and controlled to maintain a constant regulated voltage of 0.3V across the feedback resistor connected to the feedback pin (FB). The value of the resistor sets the LED current accordingly (0.3V/R1). Thermal overload protection circuitry has been included to prevent the device from operating at unsafe junction temperatures above 150ºC. In the event of a thermal overload condition the device will automatically shutdown and wait till the junction temperatures cools to 130ºC before normal operation is resumed. During the initial power-up stage, the duty cycle of the internal power switch is limited to prevent excessive in-rush currents and thereby provide a “soft-start” mode of operation. © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 7 Doc. No. MD-5026 Rev. C CAT4240 APPLICATION INFORMATION External Component Selection voltage at a given current. In order to achieve the best efficiency, this forward voltage should be as low as possible. The response time is also critical since the driver is operating at 1MHz. Central Semiconductor Schottky rectifier CMSH1-40 (1A rated) is recommended for most applications. Capacitors The CAT4240 only requires small ceramic capacitors of 4.7μF on the inductor input, 1µF on the VIN pin and 1µF on the output. Under normal condition, a 4.7µF input capacitor is sufficient. For applications with higher output power, a larger input capacitor of 10µF may be appropriate. X5R and X7R capacitor types are ideal due to their stability across temperature range. LED Current Setting The LED current is set by the external resistor R1 connected between the feedback pin (FB) and ground. The formula below gives the relationship between the resistor and the current: Inductor A 47µH inductor is recommended for most of the CAT4240 applications. In cases where the efficiency is critical, inductances with lower series resistance are preferred. Inductors with current rating of 800mA or higher are recommended for most applications. Sumida CDRH6D28-470 47µH inductor has a rated current of 800mA and a series resistance (D.C.R.) of 176mΩ typical. R1 = 0.3V/LED current LED current (mA) 20 25 30 100 300 Schottky Diode The current rating of the Schottky diode must exceed the peak current flowing through it. The Schottky diode performance is rated in terms of its forward Doc. No. MD-5026 Rev. C R1 (Ω) 15 12 10 3 1 Table 1. Resistor R1 and LED current 8 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4240 OPEN LED PROTECTION In the event of an “Open LED” fault condition, the CAT4240 will continue to boost the output voltage with maximum power until the output voltage reaches approximately 40V. Once the output exceeds this level, the internal circuitry immediately places the device into a very low power mode where the total input power is limited to about 6mW (about 1.6mA input current with a 3.6V supply). The SW pin clamps at a voltage below its maximum rating of 60V. There is no need to use an external zener diode between Vout and the FB pin. A 50V rated C2 capacitor is required to prevent any overvoltage damage in the open LED condition. Open LED Disconnect and Reconnect Open LED Protection without Zener Open LED Disconnect Schottky 100V (Central CMSH1-100) L VL 13V 47µH C1 VOUT C2 4.7µF SW VIN 5V VIN ON OFF SHDN 1µF CAT4240 FB R1 3Ω Open LED Supply Current vs. VIN without Zener Open LED Output Voltage vs. VIN without Zener 5.0 60 OUTPUT VOLTAGE [V] INPUT CURRENT [mA] GND 4.0 3.0 2.0 1.0 VIN = 5V 0.0 8 50 45 40 9 10 11 12 13 14 15 16 INDUCTOR VOLTAGE [V] © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 55 8 9 9 10 11 12 13 14 15 16 INDUCTOR VOLTAGE [V] Doc. No. MD-5026 Rev. C CAT4240 DIMMING CONTROL Filtered PWM Signal A filtered PWM signal used as a variable DC voltage can control the LED current. Figure 2 shows the PWM control circuitry connected to the CAT4240 FB pin. The PWM signal has a voltage swing of 0V to 2.5V. The LED current can be dimmed within a range from 0mA to 20mA. The PWM signal frequency can vary from very low frequency up to 100kHz. There are several methods available to control the LED brightness. ¯¯¯¯¯ Pin PWM signal on the SHDN LED brightness dimming can be done by applying a ¯¯¯¯¯ input. The LED current is PWM signal to the SHDN repetitively turned on and off, so that the average current is proportional to the duty cycle. A 100% duty ¯¯¯¯¯ always high, corresponds to the cycle, with SHDN LEDs at nominal current. Figure 1 shows a 1kHz ¯¯¯¯¯ pin. signal with a 50% duty cycle applied to the SHDN The recommended PWM frequency range is from 100Hz to 2kHz. VIN SW CAT4240 SHDN GND PWM 2.5V Signal 0V LED Current FB RA 3.73kΩ VFB = 300mV VIN RB 3.1kΩ C3 0.22µF R2 1kΩ R1 15Ω Figure 2. Circuit for Filtered PWM Signal A PWM signal at 0V DC, or a 0% duty cycle, results in a max LED current of about 22mA. A PWM signal with a 93% duty cycle or more, results in an LED current of 0mA. 25 LED CURRENT [mA] Figure 1. Switching Waveform ¯¯¯¯¯ with 1kHz PWM on SHDN 20 15 10 5 0 0 10 20 30 40 50 60 70 80 90 100 PWM DUTY CYCLE [%] Figure 3. Filtered PWM Dimming [0V to 2.5V] Doc. No. MD-5026 Rev. C 10 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4240 BOARD LAYOUT The CAT4240 is a high-frequency switching regulator. The traces that carry the high-frequency switching current have to be carefully laid out on the board in order to minimize EMI, ripple and noise in general. The thicker lines on Figure 4 show the switching current path. All these traces have to be short and wide enough to minimize the parasitic inductance and resistance. The loop shown on Figure 4 corresponds to the current path when the CAT4240 internal switch is closed. On Figure 5 is shown the current loop, when the CAT4240 switch is open. Both loop areas should be as small as possible. L D Capacitor C1 has to be placed as close as possible to the VIN pin and GND. The capacitor C2 has to be connected separately to the top LED anode. A ground plane under the CAT4240 allows for direct connection of the capacitors to ground. The resistor R1 must be connected directly to the GND pin of the CAT4240 and not shared with the switching current loops and any other components. VOUT L VIN D VOUT VIN SW SW VIN VIN CAT4240 Switch Closed SHDN CAT4240 FB SHDN C2 C1 R1 FB C2 C1 GND Switch Open R1 GND Figure 4. Closed-switch Current Loop Figure 5. Open-switch Current Loop Figure 6. Recommended PCB Layout © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 11 Doc. No. MD-5026 Rev. C CAT4240 PACKAGE OUTLINE DRAWING TSOT-23 5-Lead (TD) (1)(2) SYMBOL D MIN NOM A1 0.01 0.05 A2 0.80 0.87 b 0.30 c 0.12 MAX A e 1.00 D E1 E 0.10 0.90 0.45 0.15 0.20 2.90 BSC E 2.80 BSC E1 1.60 BSC e 0.95 TYP L 0.30 L1 0.40 0.50 0.60 REF L2 0.25 BSC θ 0º 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-5026 Rev. C 12 © Catalyst Semiconductor, Inc. Characteristics subject to change without notice CAT4240 EXAMPLE OF ORDERING INFORMATION Prefix CAT Device # 4240 (1) Suffix TD Product Number 4240 – G Lead Finish G: NiPdAu T3 Tape & Reel T: Tape & Reel 3: 3000/Reel Optional Company ID Package TD: Thin SOT-23 (Lead-free, Halogen-free) SERIES LED DRIVERS Part Number Description CAT4137 CMOS Boost Converter – White LED Driver CAT4237 High Voltage CMOS Boost White LED Driver CAT4238 High Efficiency 10 LED Boost Converter CAT4139 22V High Current Boost White LED Driver CAT4240 6 Watt Boost LED Driver 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 CAT4240–GT3 (TSOT-23, NiPdAu, Tape & Reel). (4) For additional package and temperature options, please contact your nearest Catalyst Semiconductor Sales office. -free, Halogen-free). (5) Switch current limit, typical values. © Catalyst Semiconductor, Inc. Characteristics subject to change without notice 13 Doc. No. MD-5026 Rev. C REVISION HISTORY Date Rev. 05/31/2007 A 10/17/2007 B 11/06/07 C Reason Initial Issue Update Absolute Maximum Ratings Update Package Outline Drawing Update Simplified Block Diagram Update Device Operation text Update Board Layout figure numbers Update Series LED Drivers table 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 www.catsemi.com Document No: MD-5026 Revision: C Issue date: 11/06/07