CAT4240 6 Watt Boost LED Driver Description 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 1 MHz 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 (1 mm max height) 5−lead thin SOT23 package for space critical applications. http://onsemi.com 5 1 TSOT−23 TD SUFFIX CASE 419AE PIN CONNECTIONS 1 GND Features • • • • • • • • • • • • VIN SW SHDN FB Switch Current Limit 750 mA Drives High Voltage LED Strings (38 V) Up to 94% Efficiency Low Quiescent Ground Current 0.6 mA 1 MHz Fixed Frequency Low Noise Operation Soft Start “In−rush” Current Limiting Shutdown Current Less than 1 mA Open LED Overvoltage Protection Automatic Shutdown at 1.9 V (UVLO) Thermal Overload Protection Thin SOT23 5−lead (1 mm Max Height) These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS Compliant (Top View) MARKING DIAGRAM TGYM TG = Specific Device Code Y = Production Year (Last Digit) M = Production Month (1−9, A, B, C) ORDERING INFORMATION Device CAT4240TD−GT3 Applications • GPS Navigation Systems • Portable Media Players • Handheld Devices, Digital Cameras Shipping TSOT−23 (Pb−Free) Green* 3,000/ Tape & Reel * NiPdAu Plated Finish L1 VL 8 V to 16 V VIN 5V Package D1 47 mH C1 C2 4.7 mF/16 V C3 1 μF SW VIN VOUT 1 μF/50 V CAT4240 SHDN GND FB 300 mA R2 (300 mV) 1 kW L1: Sumida CDRH6D28−470 D1: Central CMSH1−40 (rated 40 V) R1 1W Figure 1. Typical Application Circuit © Semiconductor Components Industries, LLC, 2010 February, 2010 − Rev. 3 1 Publication Order Number: CAT4240/D CAT4240 Table 1. ABSOLUTE MAXIMUM RATINGS Parameters Ratings Units VIN, FB voltage −0.3 to +7 V SHDN voltage −0.3 to +7 V SW voltage −0.3 to 60 V Storage Temperature Range −65 to +160 _C Junction Temperature Range −40 to +150 _C 300 _C Lead Temperature 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 2. RECOMMENDED OPERATING CONDITIONS Parameters VIN SW pin voltage Ambient Temperature Range (Note 1) Range Units up to 5.5 V 0 to 38 V −40 to +85 _C NOTE: Typical application circuit with external components is shown on page 1. 1. Thin SOT23−5 package thermal resistance qJA = 135°C/W when mounted on board over a ground plane. Table 3. DC ELECTRICAL CHARACTERISTICS (VIN = 3.6 V, ambient temperature of 25°C (over recommended operating conditions unless otherwise specified)) Symbol Parameter Test Conditions Min Typ Max Units IQ Operating Current VFB = 0.2 V VFB = 0.4 V (not switching) 0.6 0.1 1.5 0.6 mA ISD Shutdown Current VSHDN = 0 V 0.1 1 mA VFB FB Pin Voltage 6 LEDs with ILED = 75 mA 285 300 315 mV IFB FB pin input leakage 1 mA ILED Programmed LED Current R1 = 10 W R1 = 5 W 28.5 30 60 31.5 mA 0.4 0.8 0.7 1.5 V 0.8 1.0 1.3 MHz VIH VIL SHDN Logic High SHDN Logic Low Enable Threshold Level Shutdown Threshold Level FSW Switching Frequency DC Maximum Duty Cycle VIN = 3 V ILIM Switch Current Limit VIN = 3.6 V VIN = 5 V RSW Switch “On” Resistance ISW = 100 mA ILEAK Switch Leakage Current Switch Off, VSW = 30 V 92 % 600 750 mA 1.0 2.0 W 2 5 mA Thermal Shutdown 150 °C Thermal Hysteresis 20 °C VUVLO Undervoltage Lockout (UVLO) Threshold 1.9 V VOV-SW Overvoltage Detection Threshold 40 V 42 V VOCL Output Voltage Clamp “Open LED” http://onsemi.com 2 CAT4240 TYPICAL CHARACTERISTICS (VIN = 5 V, VL = 13 V, TAMB = 25°C, typical application circuit unless otherwise specified.) 2.0 VFB = 0.4 V QUIESCENT CURRENT (mA) QUIESCENT CURRENT (mA) 200 150 100 50 3.0 3.5 4.0 4.5 5.0 1.5 1.0 0.5 0 5.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Figure 2. Quiescent Current vs. VIN (Not Switching) Figure 3. Quiescent Current vs. VIN (Switching) 5.5 310 303 FB PIN VOLTAGE (mV) FB PIN VOLTAGE (mV) 302 301 300 299 305 300 295 298 4 LEDs 297 −50 0 50 100 290 150 100 150 OUTPUT CURRENT (mA) Figure 4. FB Pin Voltage vs. Temperature Figure 5. FB Pin Voltage vs. Output Current 200 2.0 SWITCH RESISTANCE (W) SWITCHING FREQUENCY (MHz) 50 TEMPERATURE (°C) 1.2 1.1 1.0 0.9 0.8 0 3.0 3.5 4.0 4.5 5.0 1.5 1.0 0.5 0 5.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Figure 6. Switching Frequency vs. Supply Voltage Figure 7. Switch ON Resistance vs. Input Voltage http://onsemi.com 3 5.5 CAT4240 TYPICAL CHARACTERISTICS (VIN = 5 V, VL = 13 V, TAMB = 25°C, typical application circuit unless otherwise specified.) 2.0 350 LED CURRENT (mA) 300 250 200 RSET = 2 W VOUT = 18.8 V 150 100 8 9 10 11 12 13 14 15 1.5 1.0 0.5 0 −0.5 −1.0 −1.5 −2.0 16 8 9 10 11 12 13 14 INDUCTOR VOLTAGE (V) Figure 8. LED Current vs. Input Voltage Figure 9. LED Current Regulation 100 100 95 95 90 85 80 6 LEDs @ 150 mA INDUCTOR VOLTAGE (V) EFFICIENCY (%) EFFICIENCY (%) LED CURRENT VARIATION (%) RSET = 1 W VOUT = 19.5 V 15 16 15 16 90 85 50 100 150 200 250 80 300 8 9 10 11 12 13 14 LED CURRENT (mA) INDUCTOR VOLTAGE (V) Figure 10. Efficiency vs. Load Current (6 LEDs) Figure 11. Efficiency vs. Inductor Voltage (6 LEDs) Figure 12. Power−up with 6 LEDs at 300 mA Figure 13. Switching Waveform http://onsemi.com 4 CAT4240 TYPICAL CHARACTERISTICS (VIN = 5 V, VL = 13 V, TAMB = 25°C, typical application circuit unless otherwise specified.) 1.0 SHUTDOWN VOLTAGE (V) 400 VOUT = 20 V 300 VOUT = 30 V 200 100 8 9 10 11 12 13 14 15 −25°C 85°C 0.6 125°C 0.4 0.2 16 −40°C 0.8 3.0 3.5 4.0 4.5 INDUCTOR VOLTAGE (V) INPUT VOLTAGE (V) Figure 14. Maximum Output Current Figure 15. Shutdown Voltage 1200 SW CURRENT LIMIT (mA) MAX OUTPUT CURRENT (mA) 500 1100 1000 900 800 VOUT = 20 V 700 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) Figure 16. Switch Current Limit http://onsemi.com 5 5.0 5.5 5.0 CAT4240 Pin Description VIN is the supply input for the internal logic. The device is compatible with supply voltages down to 2.8 V and up to 5.5 V. It is recommended that a small bypass ceramic capacitor (4.7 mF) be placed between the VIN and GND pins near the device. If the supply voltage drops below 1.9 V, the device stops switching. SHDN is the shutdown logic input. When the pin is tied to a voltage lower than 0.4 V, the device is in shutdown mode, drawing nearly zero current. When the pin is connected to a voltage higher than 1.5 V, the device is enabled. GND is the ground reference pin. This pin should be connected directly to the ground plane on the PCB. 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 over-voltage detection circuit is connected to the SW pin. When the voltage reaches 40 V, the device enters a low power operating mode preventing the SW voltage from exceeding the maximum rating. FB feedback pin is regulated at 0.3 V. A resistor connected between the FB pin and ground sets the LED current according to the formula: I LED + 0.3 V R1 The lower LED cathode is connected to the FB pin. Table 4. PIN DESCRIPTIONS Pin # Name 1 SW 2 GND 3 FB 4 SHDN 5 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 VIN VOUT SW C1 C2 1 MHz Oscillator Ref 300 mV – + PWM & Logic + – Current Sense – SHDN Thermal Shutdown & UVLO + VIN Over Voltage Protection Driver LED Current RS GND FB R1 Figure 17. Simplified Block Diagram http://onsemi.com 6 CAT4240 Device Operation The CAT4240 is a fixed frequency (1 MHz), 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. The on/off duty cycle of the power switch is internally adjusted and controlled to maintain a constant regulated voltage of 0.3 V across the feedback resistor connected to the feedback pin (FB). The value of the resistor sets the LED current accordingly (0.3 V/R1). 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. When the inductor is connected to a 9 V supply or higher, the CAT4240 can drive 6 LEDs in series at 300 mA delivering a total power of 6 Watts into the load. A separate 5 V 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 40 V, an internal protection circuit will become active and place the device into a very low power safe operating mode. Thermal overload protection circuitry has been included to prevent the device from operating at unsafe junction temperatures above 150°C. In the event of a thermal overload condition the device will automatically shutdown and wait till the junction temperatures cools to 130°C before normal operation is resumed. Application Information External Component Selection Capacitors forward voltage should be as low as possible. The response time is also critical since the driver is operating at 1 MHz. Central Semiconductor Schottky rectifier CMSH1−40 (1 A rated) is recommended for most applications. The CAT4240 only requires small ceramic capacitors of 4.7 mF on the inductor input, 1 mF on the VIN pin and 1 mF on the output. Under normal condition, a 4.7 mF input capacitor is sufficient. For applications with higher output power, a larger input capacitor of 10 mF 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 47 mH 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 800 mA or higher are recommended for most applications. Sumida CDRH6D28−470 47 mH inductor has a rated current of 800 mA and a series resistance (D.C.R.) of 176 mW typical. R1 + 0.3 V current LED Table 5. RESISTOR R1 AND LED CURRENT LED Current (mA) R1 (W) 20 15 25 12 30 10 100 3 300 1 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 voltage at a given current. In order to achieve the best efficiency, this http://onsemi.com 7 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 40 V. 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 6 mW (about 1.6 mA input current with a 3.6 V supply). The SW pin clamps at a voltage below its maximum rating of 60 V. There is no need to use an external zener diode between Vout and the FB pin. A 50 V rated C2 capacitor is required to prevent any overvoltage damage in the open LED condition. Schottky 100 V (Central CMSH1−100) L VL VOUT 47 mH 13 V C1 C2 4.7 mF VIN VIN 5V 1 mF SW CAT4240 ON OFF SHDN GND FB R1 3W Figure 18. Open LED Protection without Zener 60 4.0 OUTPUT VOLTAGE (V) INPUT CURRENT (mA) 5.0 3.0 2.0 1.0 55 50 45 VIN = 5 V 0 8 9 10 11 12 13 14 15 40 16 8 9 10 11 12 13 14 15 INDUCTOR VOLTAGE (V) INDUCTOR VOLTAGE (V) Figure 19. Open LED Supply Current vs. VIN without Zener Figure 20. Open LED Output Voltage vs. VIN without Zener Figure 21. Open LED Disconnect and Reconnect Figure 22. Open LED Disconnect http://onsemi.com 8 16 CAT4240 Dimming Control There are several methods available to control the LED brightness. VIN SW CAT4240 PWM Signal on the SHDN Pin LED brightness dimming can be done by applying a PWM signal to the SHDN input. The LED current is repetitively turned on and off, so that the average current is proportional to the duty cycle. A 100% duty cycle, with SHDN always high, corresponds to the LEDs at nominal current. Figure 23 shows a 1 kHz signal with a 50% duty cycle applied to the SHDN pin. The recommended PWM frequency range is from 100 Hz to 2 kHz. SHDN GND PWM Signal 2.5 V VIN 0V FB 3.73 kW 3.1 kW RA RB VFB = 300 mV 1 kW LED Current R2 R1 15 W C3 0.22 mF Figure 24. Circuit for Filtered PWM Signal A PWM signal at 0 V DC, or a 0% duty cycle, results in a max LED current of about 22 mA. A PWM signal with a 93% duty cycle or more, results in an LED current of 0 mA. LED CURRENT (mA) 25 Figure 23. Switching Waveform with 1 kHz PWM on SHDN 20 15 10 5 0 Filtered PWM Signal A filtered PWM signal used as a variable DC voltage can control the LED current. Figure 24 shows the PWM control circuitry connected to the CAT4240 FB pin. The PWM signal has a voltage swing of 0 V to 2.5 V. The LED current can be dimmed within a range from 0 mA to 20 mA. The PWM signal frequency can vary from very low frequency up to 100 kHz. 0 10 20 30 40 50 60 70 80 90 100 PWM DUTY CYCLE (%) Figure 25. Filtered PWM Dimming (0 V to 2.5 V) http://onsemi.com 9 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 26 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 26 corresponds to the current path when the CAT4240 internal switch is closed. On Figure 27 is shown VIN L D the current loop, when the CAT4240 switch is open. Both loop areas should be as small as possible. 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 SW SW VIN VIN CAT4240 Switch Closed SHDN CAT4240 FB SHDN C2 C1 R1 C1 GND GND Figure 26. Closed−switch Current Loop Switch Open FB C2 Figure 27. Open−switch Current Loop Figure 28. Recommended PCB Layout http://onsemi.com 10 R1 CAT4240 PACKAGE DIMENSIONS TSOT−23, 5 LEAD CASE 419AE−01 ISSUE O SYMBOL D MIN NOM A1 0.01 0.05 0.10 A2 0.80 0.87 0.90 b 0.30 c 0.12 A e E1 1.00 0.45 0.15 D 2.90 BSC E 2.80 BSC E1 1.60 BSC E MAX e 0.20 0.95 TYP L 0.30 0.40 L1 0.60 REF L2 0.25 BSC 0º θ 0.50 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 11 L2 CAT4240 Example of Ordering Information (Note 4) Prefix Device # Suffix CAT 4240 TD −G T3 Company ID (Optional) Product Number 4240 Package TD: Thin SOT−23 (Lead−free, Halogen−free) Lead Finish G: NiPdAu Tape & Reel (Note 7) T: Tape & Reel 3: 3,000 / Reel SERIES LED DRIVERS ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ ÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁÁ Part Number 2. 3. 4. 5. 6. 7. Description CAT4137 CMOS Boost Converter − White LED Driver CAT4237 High Voltage CMOS Boost White LED Driver CAT4238 High Efficiency 10 LED Boost Converter CAT4139 22 V High Current Boost White LED Driver CAT4240 6 Watt Boost LED Driver All packages are RoHS−compliant (Lead−free, Halogen−free). The standard lead finish is NiPdAu. The device used in the above example is a CAT4240TD−GT3 (TSOT−23, NiPdAu, Tape & Reel, 3,000/Reel). For additional package and temperature options, please contact your nearest ON Semiconductor Sales office. Switch current limit, typical values. For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD8011/D. ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. 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