CAV4201 350 mA High Efficiency Step Down LED Driver Description The CAV4201 is a high efficiency step−down converter optimized to drive high current LEDs. A patented switching control algorithm allows highly efficient and accurate LED current regulation. A single RSET resistor sets the full scale LED string current up to 350 mA from supplies as high as 36 V. The switching architecture of the CAV4201 results in extremely low internal power dissipation allowing the device to be housed in a tiny package without the need for dedicated heat sinking. The device is compatible with switching frequencies of up to 1 MHz, making it ideal for applications requiring small footprint and low value external inductors. Enable, analog dimming and LED shutdown control is provided via a single input pin, CTRL. Additional features include overload current protection and thermal shutdown. The device is available in the low profile 5−lead thin SOT23 package and is ideal for space constrained applications. http://onsemi.com 5 1 TSOT−23 TD SUFFIX CASE 419AE PIN CONNECTIONS 1 GND SW RSET Features • • • • • • • • • • • (Top View) LED Drive Current up to 350 mA Compatible with 12 V and 24 V Standard Systems Handles Transients up to 40 V Single Pin Control and Dimming Function Power Efficiency up to 94% Drives LED Strings of up to 32 V Open and Short LED Protection Parallel Configuration for Higher Output Current CAV Prefix for Automotive and Other Applications requiring Site and Change Control TSOT−23 5−lead Package These Devices are Pb−Free, Halogen Free/BFR Free and are RoHS Compliant MARKING DIAGRAMS TFYM TF = Device Code Y = Production Year (Last Digit) M = Production Month: 1−9, A, B, C ORDERING INFORMATION Device CAV4201TD−GT3 Applications • • • • VBAT CTRL Package Shipping TSOT−23 (Pb−Free) 3,000/ Tape & Reel * Plated Finish: NiPdAu 12 V and 24 V Lighting Systems Automotive and Aircraft Lighting General Lighting High Brightness 350 mA LEDs VBAT 9V C1 4.7 mF VBAT CAV4201 Enable / Analog Dimming R1 D C2 10 mF 350 mA CTRL L RSET SW GND 22 mH D: ON Semiconductor MBR0540 L: Sumida CDRH6D26−220 See Table 4 and Table 5 for external component selection. Figure 1. Typical Application Circuit © Semiconductor Components Industries, LLC, 2011 November, 2011 − Rev. 1 1 Publication Order Number: CAV4201/D CAV4201 Table 1. ABSOLUTE MAXIMUM RATINGS Parameters Ratings Units VBAT, SW, CTRL −0.3 to +40 V RSET −0.3 to +5 V 1 A Storage Temperature Range −65 to +160 _C Junction Temperature Range −40 to +150 _C 300 _C Switch SW peak current 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 VBAT voltage (Notes 1, 2) Ratings Units 6.5 to 36 (Note 1) V SW voltage 0 to 36 V −40 to +125 _C LED Current 50 to 350 mA Switching Frequency 50 to 1000 kHz Ambient Temperature Range 1. The VBAT pin voltage should be at least 3 V greater than the total sum of the LED forward voltages in order to operate at nominal LED current. 2. During power−up, the slew rate of the input supply should be greater than 1 ms for every 5 V increase of VBAT. Table 3. ELECTRICAL CHARACTERISTICS (VIN = 13 V, ambient temperature of 25°C (over recommended operating conditions unless otherwise specified)) Symbol Parameter Conditions Min Typ Max Units 0.4 1 mA IQ Operating Supply Current on VBAT pin ISD Idle Mode Supply Current on VBAT pin CTRL = GND VFB RSET Pin Voltage 2 LEDs with ILED = 300 mA 1.15 1.2 1.25 ILED Programmed LED Current R1 = 33 kW R1 = 10 kW R1 = 8.25 kW 270 100 300 350 330 2.6 3.1 V 0.9 1.2 V VCTRL−FULL 90 CTRL Voltage for 100% Brightness mA V mA VCTRL−EN CTRL Voltage to Enable LEDs LED enable voltage threshold VCTRL−SD CTRL Voltage to Shutdown LEDs LED disable voltage threshold ICTRL CTRL pin input bias VCTRL = 3 V VCTRL = 12 V 40 200 80 RSW Switch “On” Resistance ISW = 300 mA 0.9 1.5 TSD Thermal Shutdown 150 °C THYST Thermal Hysteresis 20 °C 86 % h Efficiency Typical Application Circuit http://onsemi.com 2 0.4 0.9 V mA W CAV4201 TYPICAL OPERATION CHARACTERISTICS (VIN = 13 V, ILED = 300 mA, L = 22 mH, C1 = 4.7 mF, C2 = 10 mF, TAMB = 25°C unless otherwise specified) 200 0.8 IDLE CURRENT (mA) QUIESCENT CURRENT (mA) 1.0 0.6 0.4 0.2 0 8 10 12 14 16 18 20 22 50 0 4 8 12 16 20 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Figure 2. Input Operating Supply Current Figure 3. Idle Mode Supply Current (CTRL = 0 V) 24 1.30 VIN = 13 V 200 RSET VOLTAGE (V) CTRL BIAS CURRENT (mA) 100 0 24 250 150 100 50 0 150 0 2 4 6 8 10 1.25 1.20 1.15 1.10 −40 12 0 40 80 120 CTRL VOLTAGE (V) TEMPERATURE (°C) Figure 4. CTRL Input Bias Current Figure 5. RSET Voltage vs. Temperature 400 1.4 LED CURRENT (mA) RSET VOLTAGE (V) 1.2 1.0 0.8 +25°C −40°C +85°C 0.6 0.4 300 200 100 0.2 0 0 1 2 3 0 4 5 10 15 20 25 30 CTRL VOLTAGE (V) RSET (kW) Figure 6. RSET Voltage vs. CTRL Voltage Figure 7. LED Current vs. RSET http://onsemi.com 3 35 CAV4201 TYPICAL OPERATION CHARACTERISTICS (VIN = 13 V, ILED = 300 mA, L = 22 mH, C1 = 4.7 mF, C2 = 10 mF, TAMB = 25°C unless otherwise specified) 700 SWITCHING FREQUENCY (kHz) SWITCHING FREQUENCY (kHz) 500 150 mA 400 300 300 mA 200 100 0 8 12 16 20 24 400 300 mA 300 200 100 8 12 16 20 24 28 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Figure 8. Switching Frequency vs. Input Voltage (1 LED) Figure 9. Switching Frequency vs. Input Voltage (2 LEDs) 2.0 VIN = 13 V SW RESISTANCE (W) 150 mA 400 300 300 mA 200 100 −40 0 40 80 1.6 1.2 0.8 0.4 0 120 14 16 18 20 22 Figure 11. Switch ON Resistance vs. Input Voltage 95 95 90 150 mA 300 mA 24 150 mA 90 300 mA 85 80 75 75 70 12 Figure 10. Switching Frequency vs. Temperature 100 80 10 INPUT VOLTAGE (V) 100 85 8 TEMPERATURE (°C) EFFICIENCY (%) SWITCHING FREQUENCY (kHz) 150 mA 500 0 28 500 EFFICIENCY (%) 600 8 10 12 14 16 18 20 22 70 24 8 10 12 14 16 18 20 22 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Figure 12. Efficiency vs. Input Voltage (1 LED) Figure 13. Efficiency vs. Input Voltage (2 LEDs) http://onsemi.com 4 24 CAV4201 TYPICAL OPERATION CHARACTERISTICS (VIN = 13 V, ILED = 300 mA, L = 22 mH, C1 = 4.7 mF, C2 = 10 mF, TAMB = 25°C unless otherwise specified) 10 LED CURRENT VARIATION (%) 100 EFFICIENCY (%) 95 2 LEDs 90 85 1 LED 80 75 70 100 150 200 250 300 350 6 4 2 0 −2 −4 −6 −8 −10 −40 0 40 80 120 TEMPERATURE (°C) Figure 14. Efficiency vs. LED Current Figure 15. LED Current Regulation vs. Temperature 350 VF = 3.3 V 300 300 mA 250 200 VF = 3.1 V 150 VF = 3.3 V 300 LED CURRENT (mA) LED CURRENT (mA) VIN = 13 V LED CURRENT (mA) 350 150 mA 100 50 0 8 300 mA 250 200 VF = 3.1 V 150 150 mA 100 50 0 4 8 12 16 20 24 0 28 0 4 8 12 16 20 24 INPUT VOLTAGE (V) INPUT VOLTAGE (V) Figure 16. LED Current vs. Input Voltage (1 LED) Figure 17. LED Current vs. Input Voltage (2 LEDs) SW 5V/div CTRL 5V/div Inductor Current 200mA/ div LED Current 200mA/ div 2 ms/div 40 ms/div Figure 18. Switching Waveforms Figure 19. CTRL Power−up http://onsemi.com 5 28 CAV4201 TYPICAL OPERATION CHARACTERISTICS (VIN = 13 V, ILED = 300 mA, L = 22 mH, C1 = 4.7 mF, C2 = 10 mF, TAMB = 25°C unless otherwise specified) Figure 20. RSET Transient Response Figure 21. Line Transient Response (10 V to 13 V) External Component Selection Table 4 provides the recommended external components L and C2 that offer the best performance relative to the LED current accuracy, LED ripple current, switching frequency and component size. Table 4. EXTERNAL COMPONENT SELECTION 1 LED 2 LEDs LED Current (mA) L Inductor (mH) C2 Capacitor (mF) L Inductor (mH) C2 Capacitor (mF) ≥150 22 4.7 22 4.7 < 150 33 4.7 47 2.2 47 10 NOTE: Larger C2 capacitor values allow to reduce further the LED ripple current if needed. Table 5. INDUCTOR SELECTION DEPENDING ON VBAT SUPPLY VOLTAGE VBAT Supply Voltage (V) Minimum Inductor L (mH) < 26 22 ≥ 26 33 http://onsemi.com 6 CAV4201 Table 6. PIN DESCRIPTION Pin Name 1 CTRL Enable and analog dimming control input pin. 2 GND Ground reference. 3 RSET RSET pin. A resistor connected between the pin and ground sets the average LED current. 4 SW 5 VBAT Function Interface to the inductor. Supply voltage for the device. Pin Function VBAT is the supply input to the device. Typical current conduction into this pin is less than 1 mA and voltage transients of up to 40 V can be applied. To ensure accurate LED current regulation, the VBAT voltage should be 3 V higher than the total forward voltage of the LED string. A bypass capacitor of 4.7 mF or larger is recommended between VBAT and GND. CTRL is the enable and analog dimming control input. An internal pull−down current of 20 mA allows the LEDs to shutdown if CTRL is left floating. Voltages of up to 40 V can be safely handled by the CTRL input pin. When the CTRL voltage is less than 0.9 V (typ), the LEDs will shutdown to zero current. When the CTRL voltage is greater than about 2.6 V, the device is enabled and full scale brightness is applied to the LED output. At voltages of less than around 2.6 V, the LED current is progressively dimmed until shutdown. For lamp replacement applications, or applications where operation in dropout mode is expected, it is recommended that the CTRL pin voltage be derived from the LED cathode terminal. 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 high−voltage power MOSFET. The inductor and the Schottky diode anode should be connected to the SW pin. Voltages of up to 40 V can be safely handled on the SW pin. Traces going to the SW pin should be as short as possible with minimum loop area. The device can handle safely “open−LED” or “shorted−LED” fault conditions. RSET pin is regulated at 1.2 V. A resistor connected between the RSET pin and ground sets the LED full−scale brightness current. The external resistance value and the CTRL pin voltage determine the LED current during analog dimming. The RSET pin must not be left floating. The highest recommended resistor value between RSET and ground is 90 kW. http://onsemi.com 7 CAV4201 Simplified Block Diagram 12 V/24 V VBAT 30 kW CTRL 7V 20 mA OFF−Time Control SW EN PWM Controller 1.2 V Reference + ON−Time Control EN – R2 1W 1.2 V RSET GND Figure 22. CAV4201 Simplified Block Diagram Basic Operation The CAV4201 is a high efficiency step−down regulator designed to drive series connected high−power LEDs. LED strings with total forward voltages of up to 32 V can be driven with bias currents of up to 350 mA. During the first switching phase, an integrated high voltage power MOSFET allows the inductor current to charge linearly until the peak maximum level is reached, at which point the MOSFET is switched off and the second phase commences, allowing the inductor current to then flow through the Schottky diode circuit and discharge linearly back to zero current. The switching architecture ensures the device will always operate at the cross−over point between Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM). This operating mode results in an average LED current which is equal to half of the peak switching current. LED Pin Current The LED current is set by the external RSET resistor connected to the regulated output of the RSET pin. An overall current gain ratio of approximately 2.5 A/mA exists between the average LED current and the RSET current, hence the following equation can be used to calculate the LED current. LED Current (A) ^ 2.5 V RSET (V) R SET (kW) Table 7 lists the various LED currents and the associated RSET resistors. Table 7. RSET RESISTOR SELECTION http://onsemi.com 8 LED Current (A) RSET (kW) 0.10 33 0.15 21 0.20 15 0.25 12 0.30 10 0.35 8.25 CAV4201 APPLICATION INFORMATION Capacitor Selection A 10 mF ceramic capacitor C2 across the LED(s) keeps the LED ripple current within ±15% of nominal for most applications. If needed, a larger capacitor can be used to further reduce the LED current ripple. Any resistance in series with the LED (0.5 W or more) contributes to reduce the ripple current. The capacitor voltage rating should be equivalent to the maximum expected supply voltage so as to allow for “Open−LED” fault conditions. The capacitor value is independent of the switching frequency or the overall efficiency. A 4.7 mF ceramic input capacitor C1 is recommended to minimize the input current ripple generated on the supply. Using a larger capacitor value further reduces the ripple noise appearing on the supply rail. If a constant capacitance is needed across temperature and voltage, X5R or X7R dielectric capacitors are recommended. Input Voltage Range The minimum supply voltage required to maintain adequate regulation is set by the cathode terminal voltage of the LED string (i.e., the VBAT voltage minus the LED string voltage). When the LED cathode terminal falls below 3 V, a loss of regulation occurs. For applications which may occasionally need to experience supply “dropout” conditions, it is recommended that the CTRL input be used to sense the LED cathode voltage. The CTRL pin can either be tied directly to the cathode terminal (for Lamp Replacement) or connected via a pass−transistor for PWM lighting applications. Figure 23 shows the regulation performance obtained in dropout, when the CTRL pin is configured to sense the LED cathode voltage. 400 LED CURRENT [mA] Schottky Diode 300 The peak repetitive current rating of the Schottky diode must be greater than the peak current flowing through the inductor. Also the continuous current rating of the Schottky must be greater than the average LED current. The voltage rating of the diode should be greater than the peak supply voltage transient preventing any breakdown or leakage. ON Semiconductor Schottky diode MBR0540 (40 V, 500 mA rated) is recommended. Schottky diodes rated at 400 mA (or higher) continuous current are fine for most applications. 300 mA 200 150 mA 100 0 0 1 2 3 4 5 NOTE: 6 CTRL VOLTAGE [V] Figure 23. “Dropout” Configured LED Current Schottky diodes with extremely low forward voltages (VF) are not recommended, as they may cause an increase in the LED current. Dimming Methods (as shown in Typical Application on page 1) Two methods for PWM dimming control on the LEDs are described below. The first method is to PWM on the control pin, the other method is to turn on and off a second resistor connected to the RSET pin and connected in parallel with R1. Inductor Selection A 22 mH minimum inductor value is required to provide suitable switching frequency across a wide range of input supply values. For LED current of 150 mA or less, a 33 mH or 47 mH inductor is more suitable. Inductor values below 22 mH should not be used. An inductor with at least 700 mA current rating must be used. Minor improvements in efficiency can be achieved by selecting inductors with lower series resistance. PWM on CTRL Pin A PWM signal from a microprocessor can be used for dimming the LEDs when tied to the CTRL pin. The duty cycle which is the ratio between the On time and the total cycle time sets the dimming factor. The recommended PWM frequency on the CTRL pin is between 100 Hz and 2 kHz. Table 8. SUMIDA INDUCTORS Part Number L (mH) I Rated (A) LED Current (A) CDRH6D26−220 22 1.0 0.35 CDRH6D28−330 33 0.92 0.35 CDRH6D28−470 47 0.8 0.35 CDRH6D28−560 56 0.73 0.35 Figure 24. PWM at 1 kHz on CTRL Pin http://onsemi.com 9 CAV4201 Operation from High Supply Voltage Above 14 V 300 For operation from a supply voltage above 14 V, it is recommended to have a slew rate of 1 ms or more for every 5 V increase in VBAT supply. When using a high supply voltage of 24 V, a 1 W or 2 W resistor in series with the supply, as shown on Figure 28, is recommended to limit the slew rate of the supply voltage. A 4.7 mF minimum ceramic capacitor is placed between the VBAT pin and ground. The combination of the series resistor R3 and input capacitor C1 acts as a low pass filter limiting the excessive in−rush currents and overvoltage transients which would otherwise occur during “hot−plug” conditions, thereby protecting the CAV4201 driver. LED CURRENT [mA] 250 200 150 100 50 0 100 80 60 40 DUTY CYCLE [%] 20 0 VBAT R3 Figure 25. LED Current vs. Duty Cycle 24 V 1 W C1 4.7 mF VBAT 12 V C1 4.7 mF VBAT CAV4201 RSET R1 10 kW 5V 0V PWM control D 10 mF 4.7 mF L 33 mH 300 mA R2 1 kW Figure 28. 24 V Application with 5 LEDs Q1 NPN Operation from High Supply Voltage of 36 V 1 kW When powering from a high supply voltage of 36 V, a 2 W resistor in series with the supply is recommended, as shown on Figure 29, to limit the slew rate of the supply voltage. Inductor value should be 33 mH or higher. R5 47 kW Figure 26. Circuit for PWM on CTRL VBAT R3 PWM on RSET Pin 36 V 2 W C1 Another dimming method is to place in parallel to R1 another resistor with a FET in series, as shown on Figure 27. R1 sets the minimum LED current corresponding to 0% duty cycle. The combined resistor of R1 and Rmax sets the maximum LED current corresponding to 100% duty cycle. 4.7 mF R1 10 kW VBAT 13 V C1 VBAT CAV4201 RSET D1 C2 2.2 mF L CTRL SW GND 47 mH 300 mA R2 4.7 mF Rmax C2 R1 22 mH R4 D1 CTRL SW GND L CTRL SW GND 1 kW R1 10 kW C2 VBAT CAV4201 RSET VBAT CAV4201 RSET R1 CTRL SW GND D OFF ON Figure 29. 36 V Application with 6 LEDs 10 mF Parallel Configuration for Driving LEDs Beyond 350 mA L 22 mH R2 PWM control 1 kW C2 Several CAV4201 devices can be connected in parallel for driving LEDs with current in excess of 350 mA. The CAV4201 driver circuits are connected to the same LED cathode. Figure 30 shows the application schematic for driving 1 A into one LED with three CAV4201 connected in parallel. Each CAV4201 is driving the LED with a current set by its RSET resistor. The resulting LED current is equal to the sum of each driver current. Q1 NPN 1 kW Figure 27. Circuit for PWM on RSET A resistor value for R1 of less than 90 kW is recommended to provide better accuracy. http://onsemi.com 10 CAV4201 VIN R5 C1 1W 4.7 μF R1 8.3 kΩ U1 VBAT CAV4201 RSET CTRL SW GND C4 D1 10 μF 1A L1 22 μH R4 1 kΩ C2 4.7 μF R2 8.3 kΩ U2 VBAT CAV4201 RSET CTRL SW GND D2 Figure 31. Open LED Mode Board Layout L2 In order to minimize EMI and switching noise, the Schottky diode, the inductor and the output capacitor C2 should all be located close to the driver IC. The input capacitor C1 should be located close to the VBAT pin and the Schottky diode cathode. The CAV4201 ground pin should be connected directly to the ground plane on the PCB. A recommended PCB layout with component location is shown on Figure 32. The LEDs are connected by two wires tied to both sides of the output capacitor C2. The LEDs can be located away from the driver if needed. 22 μH C3 4.7 μF R3 8.3 kΩ U3 VBAT CAV4201 RSET CTRL SW GND D3 L3 22 μH Figure 30. Three CAV4201 in Parallel for 1 A LED Open LED Behavior If the LEDs are not connected, the CAV4201 stops switching and draws very little current. At power−up with no load connected, the capacitor C2 is charged−up by the CAV4201. As soon as the bottom side of the capacitor (C2−) reaches 0 volt, as shown on Figure 31, the CAV4201 stops switching and remains in the idle mode only drawing about 0.4 mA current from the supply. Figure 32. Recommended PCB Layout In order to further reduce the ripple on the supply rail, an optional Pi style filter (C−L−C) can be used. A 10 mH inductor rated to the maximum supply current can be used. http://onsemi.com 11 CAV4201 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. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. “Typical” parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including “Typicals” must be validated for each customer application by customer’s technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC 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 SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer. 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