CAT4137 CMOS Boost Converter White LED Driver Description The CAT4137 is a DC/DC step-up converter that delivers a regulated output current. Operation at a constant switching frequency of 1 MHz allows the device to be used with small value external ceramic capacitors and inductor. The device drives a string of white LEDs connected in series and provides the regulated current to control the LEDs with inherent uniform brightness and matching. An external resistor R1 sets the output current and allows up to 30 mA current to be supported over a wide range of input supply voltages from 2.2 V to 5.5 V, making the device ideal for battery-powered applications. LED dimming can be done by using a DC voltage, a logic signal, or a pulse width modulation (PWM) signal. The shutdown control 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. Drives up to 5 White LEDs from 3 V Power Efficiency up to 87% Low Quiescent Ground Current 0.1 mA Adjustable Output Current (up to 30 mA) High Frequency 1 MHz Operation “Zero” Current Shutdown Mode Operates Down to 2 V (from Two AA Batteries) Soft Start Power-up Open LED Low Power Mode Automatic Shutdown at 1.9 V (UVLO) Thermal Shutdown Protection Thin SOT23 5−lead (1 mm Max Height) These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS Compliant 1 TSOT−23 TD SUFFIX CASE 419AE PIN CONNECTIONS 1 VIN SW GND SHDN FB (Top View) LXYM UEYM LX = CAT4137TD−T3 UE = CAT4137TD−GT3 Y = Production Year (Last Digit) M = Production Month (1−9, A, B, C) ORDERING INFORMATION (Note 3) Package Shipping (Note 4) CAT4137TD−T3 (Note 1) TSOT−23 (Pb−Free) 3,000/ Tape & Reel CAT4137TD−GT3 (Note 2) TSOT−23 (Pb−Free) 3,000/ Tape & Reel Device 1. Matte−Tin Plated Finish (RoHS−compliant). 2. NiPdAu Plated Finish (RoHS−compliant) Applications • • • • 5 MARKING DIAGRAMS Features • • • • • • • • • • • • • http://onsemi.com LCD Backlighting Cellular Phones Handheld Devices Digital Cameras 3. For detailed information and a breakdown of device nomenclature and numbering systems, please see the ON Semiconductor Device Nomenclature document, TND310/D, available at www.onsemi.com 4. 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. © Semiconductor Components Industries, LLC, 2011 November, 2011 − Rev. 3 1 Publication Order Number: CAT4137/D CAT4137 L VIN D VOUT 22 mH 2.2 to 5.5 V C2 C1 1 mF SW VIN 0.22 mF CAT4137 OFF ON SHDN FB GND VFB = 300 mV R1 15 W L: Murata LQH32CN220 D: Central CMDSH2-3 (rated 30 V) Figure 1. Typical Application Circuit Table 1. ABSOLUTE MAXIMUM RATINGS Parameter Rating Unit VIN, FB voltage −0.3 to +7 V SHDN voltage −0.3 to +7 V SW voltage −0.3 to +40 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 Parameter VIN SW pin voltage Ambient Temperature Range LED Bias Current http://onsemi.com 2 Range Unit 2.2 to 5.5 V 0 to 24 V −40 to +85 _C 1 to 30 mA CAT4137 Table 3. ELECTRICAL OPERATING CHARACTERISTICS (VIN = 3.6 V, ambient temperature of 25°C (over recommended operating conditions unless otherwise specified)) Symbol Parameter Conditions Min Typ Max Unit IQ Operating Current VFB = 0.3 V VFB = 0.4 V (not switching) 0.4 0.1 1.5 0.3 mA ISD Shutdown Current VSHDN = 0 V 0.1 1 mA VFB FB Pin Voltage 3 LEDs with ILED = 20 mA 300 315 mV IFB FB pin input leakage 0.1 1 mA ILED Programmed LED Current 28.5 19 14.25 30 20 15 31.5 21 15.75 mA 0.4 0.8 0.7 1.5 V VIH VIL R1 = 10 W R1 = 15 W R1 = 20 W SHDN Logic High SHDN Logic Low Enable Threshold Level Shutdown Threshold Level 285 FSW Switching Frequency 0.7 1.0 1.3 MHz ILIM Switch Current Limit 250 300 400 mA RSW Switch “On” Resistance ISW = 100 mA 1.0 2.0 W ILEAK Switch Leakage Current Switch Off, VSW = 5 V 1 5 mA TSD Thermal Shutdown THYS Thermal Hysteresis h Efficiency Typical Application Circuit VUVLO Undervoltage Lockout (UVLO) Threshold VOV-SW Output Clamp Voltage “Open LED” fault http://onsemi.com 3 150 °C 20 °C 86 % 1.9 V 29 V CAT4137 TYPICAL CHARACTERISTICS (VIN = 3.6 V, CIN = 1.0 mF, COUT = 0.22 mF, L = 22 mH with 3 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.) 120 1.00 100 SUPPLY CURRENT (mA) SUPPLY CURRENT (mA) VFB = 0.4 V 80 60 40 20 0 2.5 3.0 3.5 4.0 4.5 0.75 0.50 0.25 0 5.0 2.5 3.0 3.5 INPUT VOLTAGE (V) Figure 2. Quiescent Current vs. VIN (Not Switching) Figure 3. Quiescent Current vs. VIN (Switching) FB PIN VOLTAGE (mV) FB PIN VOLTAGE (mV) 3 LEDs 305 300 295 2.5 3.0 3.5 4.0 4.5 305 300 295 290 5.0 0 5 10 15 20 25 INPUT VOLTAGE (V) OUTPUT CURRENT (mA) Figure 4. FB Pin Voltage vs. Supply Voltage Figure 5. FB Pin Voltage vs. Output Current 30 2.0 1.10 3 LEDs at 20 mA SWITCH RESISTANCE (W) CLOCK FREQUENCY (MHz) 5.0 310 3 LEDs 1.05 1.00 0.95 0.90 4.5 INPUT VOLTAGE (V) 310 290 4.0 2.5 3.0 3.5 4.0 1.5 1.0 0.5 0 4.5 2.5 3.0 3.5 4.0 4.5 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Figure 6. Switching Frequency vs. Supply Voltage Figure 7. Switch ON Resistance vs. Input Voltage http://onsemi.com 4 5.0 CAT4137 TYPICAL CHARACTERISTICS (VIN = 3.6 V, CIN = 1.0 mF, COUT = 0.22 mF, L = 22 mH with 3 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.) 35 0.4 LED CURRENT (mA) 30 LED CURRENT VARIATION (%) RFB = 10 W 25 RFB = 15 W 20 RFB = 20 W 15 10 5 0 2.0 2.5 3.0 3.5 4.0 4.5 3.0 3.5 4.0 4.5 5.0 Figure 9. LED Current Regulation 5.5 100 90 EFFICIENCY (%) EFFICIENCY (%) 2.5 Figure 8. LED Current vs. Input Voltage (3 LEDs) 15 mA 20 mA VIN = 4.2 V VIN = 3.6 V 80 70 2.0 2.5 3.0 3.5 4.0 4.5 60 5.0 0 5 10 15 20 25 INPUT VOLTAGE (V) LED CURRENT (mA) Figure 10. Efficiency across Supply Voltage (3 LEDs) Figure 11. Efficiency across Load Current (3 LEDs) 100 90 90 EFFICIENCY (%) 100 15 mA 80 20 mA 30 VIN = 4.2 V VIN = 3.6 V 80 70 70 60 2.0 INPUT VOLTAGE (V) 70 EFFICIENCY (%) −0.2 INPUT VOLTAGE (V) 90 60 0 −0.4 5.0 100 80 0.2 2.0 2.5 3.0 3.5 4.0 4.5 60 5.0 0 5 10 15 20 25 INPUT VOLTAGE (V) LED CURRENT (mA) Figure 12. Efficiency across Supply Voltage (4 LEDs) Figure 13. Efficiency across Load Current (4 LEDs) http://onsemi.com 5 30 CAT4137 TYPICAL CHARACTERISTICS (VIN = 3.6 V, CIN = 1.0 mF, COUT = 0.22 mF, L = 22 mH with 3 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.) 1.0 SHUTDOWN VOLTAGE (V) FB PIN VOLTAGE (mV) 304 302 300 298 3 LEDs at 20 mA 296 294 −50 −25 0 25 50 75 0.4 3.0 3.5 4.0 5.0 4.5 INPUT VOLTAGE (V) Figure 14. FB Pin Voltage vs. Temperature Figure 15. Shutdown Voltage vs. Input Voltage 1.10 CLOCK FREQUENCY (MHz) 2.1 2.0 UVLO (V) 85°C 0.6 TEMPERATURE (°C) 2.2 1.9 1.8 1.7 1.6 −50 25°C 0.2 100 −40°C 0.8 −25 0 25 50 75 20 mA per LED 1.05 1.00 0.95 0.90 −50 100 −25 0 25 50 75 TEMPERATURE (°C) TEMPERATURE (°C) Figure 16. Under Voltage Lock Out vs. Temperature Figure 17. Switching Frequency vs. Temperature Figure 18. Switching Waveforms (3 LEDs in Series) Figure 19. Switching Waveforms (2 LEDs in Series) http://onsemi.com 6 100 CAT4137 TYPICAL CHARACTERISTICS (VIN = 3.6 V, CIN = 1.0 mF, COUT = 0.22 mF, L = 22 mH with 3 LEDs at 20 mA, TAMB = 25°C, unless otherwise specified.) Figure 20. Power−up with 3 LEDs at 20 mA Figure 21. Line Transient Response (3 V − 5.5 V) MAX OUTPUT CURRENT (mA) 140 120 VOUT = 10 V 100 80 60 VOUT = 17 V 40 20 0 2.0 2.5 3.0 3.5 4.0 4.5 5.0 INPUT VOLTAGE (V) Figure 22. Maximum Output Current vs. Input Voltage http://onsemi.com 7 5.5 CAT4137 Pin Description VIN is the supply input for the internal logic. The device is compatible with supply voltages down to 2.2 V and up to 5.5 V. A small bypass ceramic capacitor of 1 mF is recommended between the VIN and GND pins near the device. The under−voltage lockout (UVLO) circuitry will place the device into an idle mode (not switching) whenever the supply falls below 1.9 V. SHDN is the shutdown logic input. When the pin voltage is taken below 0.4 V, the device immediately enters shutdown mode, drawing nearly zero current. At voltages greater than 1.5 V, the device becomes fully enabled and operational. GND is the ground reference pin. This pin should be connected directly to the ground plane on the PCB. SW pin is the drain terminal of the internal low resistance power switch. 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. This pin contains over-voltage circuitry which becomes active above 24 V. In the event of an “Open−Led” fault condition, the device will enter a low power mode and the SW pin will be clamped to approximately 30 V. 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. http://onsemi.com 8 CAT4137 Device Operation The CAT4137 is a fixed frequency (1 MHz), low noise, inductive boost converter providing constant current to the load. A high voltage internal CMOS power switch is used to energize the external inductor. When the power switch is then turned off, the stored energy inductor is released into the load via the external 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 external feedback resistor connected to the feedback pin (FB). The value of external resistor will accurately set the LED bias 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. While in normal operation, the device will comfortably deliver up to 30 mA of bias current into a string of up to 5 white LEDs. In the event of a “Open-Led” fault condition, where the feedback control loop becomes open, the output voltage will continue to increase. Once this voltage exceeds 24 V, an internal protection circuit will become active and place the device into a very low power safe operating mode. In addition, an internal clamping circuit will limit the peak output voltage to 29 V. If this fault condition is repaired, the device will automatically resume normal operation. 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. VIN VOUT SW C2 C1 1 MHz Oscillator 300 mV – + Enable SHDN Thermal Shutdown & UVLO A1 Driver + RC – ILED PWM & Logic A2 N1 CC Current Sense RS GND – VREF + VIN Over Voltage Protection FB Figure 23. Block Diagram http://onsemi.com 9 R1 15 W CAT4137 Application Information External Component Selection 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 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 CMDSH2−3 (200 mA rated) or the CMDSH−3 (100 mA rated) is recommended for most applications. Capacitors The CAT4137 only requires small ceramic capacitors of 1 mF on the input and 0.22 mF on the output. The output capacitor should be rated at 30 V or greater. Under normal conditions, a 1 mF input capacitor is sufficient. For applications with higher output power, a larger input capacitor of 2.2 mF or 4.7 mF may be appropriate. X5R and X7R capacitor types are ideal due to their stability across temperature range. LED Current Setting Inductor The LED current is set by the external resistor between the feedback pin (FB) and ground. The formula below gives the relationship between the resistor and the current: A 22 mH inductor is recommended for most of the CAT4137 applications. In cases where the efficiency is critical, inductances with lower series resistance are preferred. Several inductor types from various vendors can be used. Figure 24 shows how different inductor types affect the efficiency across the load range. R1 + Table 5. RESISTOR R1 AND LED CURRENT 100 3 LEDs VIN = 3.6 V LED Current (mA) R1 (W) 5 60 10 30 15 20 20 15 25 12 30 10 EFFICIENCY (%) 90 80 SUMIDA CDRH3D16−220 MURATA LQH32CN220 PANASONIC ELJ−EA220 PANASONIC ELJ−PC220 70 60 0.3 V LED current 5 10 15 20 25 30 LED CURRENT (mA) Figure 24. Efficiency for Various Inductors http://onsemi.com 10 CAT4137 Typical Applications L VIN C1 1 mF 33 mH C2 SW VIN SHDN FB 100 1 mF CAT4137 OFF ON For best performance, a 33 mH inductor and a 1 mF output capacitor are recommended for 2−LED applications. In 2−LED configuration, the CAT4137 can be powered from two AA alkaline cells or from a Li−ion battery. VOUT 20 mA 95 VFB = 300 mV GND EFFICIENCY (%) 2.2 V to 5.0 V D R1 15 W L: Sumida CDRH3D16−330 D: Central CMDSH2-3 (rated 30 V) C2: Taiyo Yuden GMK212BJ105KG-T (rated 35 V) 90 VIN = 3.6 V 85 VIN = 3.0 V 80 75 Figure 25. CAT4137 Driving Two LEDs 70 0 10 20 30 LED CURRENT (mA) Figure 26. Efficiency vs. LED Current, Two LEDs http://onsemi.com 11 40 CAT4137 Dimming Control There are several methods available to control the LED brightness. Filtered PWM Signal A filtered PWM signal can be used as a variable DC voltage that can be used to control the LED current. Figure 29 shows the PWM control circuitry connected to the CAT4137 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 to 22 mA. The PWM signal frequency can vary from very low frequency up to 100 kHz. 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. Figures 27 and 28 show 1 kHz and 4 kHz signals with a 50% duty cycle applied to the SHDN pin. The PWM frequency range is from 100 Hz to 10 kHz. The recommended PWM frequency range is from 100 Hz to 4 kHz. VIN SW CAT4137 Switching Waveforms PWM on SHDN 2.5 V PWM Signal SHDN GND RA 4.02 kW FB RB 0V VFB = 300 mV R2 1 kW 3.3 kW C1 0.22 μF LED Current R1 15 W Figure 29. 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 100% duty cycle results in an LED current of 0 mA. LED CURRENT (mA) 25 Figure 27. PWM at 1 kHz 20 15 10 5 0 0 20 40 60 80 DUTY CYCLE (%) Figure 30. LED Current vs. Duty Cycle Figure 28. PWM at 4 kHz http://onsemi.com 12 100 CAT4137 Open LED Protection In the event of an “Open LED” fault condition, the CAT4137 will continue to boost the output voltage with maximum power until the output voltage reaches approximately 24 V. Once the output exceeds this level, internal circuitry immediately places the device into a very low power mode where the total input power consumed is less than 10 mW. L VIN In low power mode, the input supply current will typically drop to 2 mA. An internal clamping circuit will limit the subsequent output voltage to approximately 29 V. This operating mode eliminates the need for any external protection zener diode. This protection scheme also fully protects the device against any malfunction in the external Schottky diode (open-circuit). (Central CMDSH2−3) D V OUT 22 μH C1 1 μF C2 0.22 μF SW VIN CAT4137 OFF ON SHDN FB VFB = 300 mV GND R1 15 W Figure 31. Open LED Protection Figure 32. Open LED Power−up Waveforms SUPPLY CURRENT (mA) 2.5 2.0 1.5 1.0 2.5 3.0 4.0 3.5 4.5 INPUT VOLTAGE (V) Figure 33. Open LED Supply Current vs. VIN http://onsemi.com 13 5.0 CAT4137 Board Layout The CAT4137 is a high-frequency switching regulator. Traces carrying high-frequency switching current have to be carefully layout on the board in order to minimize EMI, ripple and noise in general. The thicker lines shown on Figure 34 indicate 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 34 corresponds to the current path when the CAT4137 internal switch is closed. On Figure 35 is shown L D VIN VOUT the current loop when the CAT4137 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 CAT4137 allows for direct connection of the capacitors to ground. The resistor R1 must be connected directly to the GND pin of the CAT4137 and not shared with the switching current loops and any other components. L D VOUT VIN SW SW VIN VIN CAT4137 SHDN C1 Switch Closed CAT4137 FB SHDN C2 R1 C1 GND GND Figure 34. Closed−switch Current Loop Switch Open FB C2 Figure 35. Open−switch Current Loop http://onsemi.com 14 R1 CAT4137 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 L2 L1 SIDE VIEW END VIEW Notes: (1) All dimensions are in millimeters. Angles in degrees. (2) Complies with JEDEC MO-193. 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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