CAT ma High Efficiency Step Down LED Driver

Transcription

1 CAT21 35 ma High Efficiency Step Down ED Driver Description The CAT21 is a high efficiency step down converter optimized to drive high current EDs. A patented switching control algorithm allows highly efficient and accurate ED current regulation. A single resistor sets the full scale ED string current up to 35 ma from supplies as high as 36 V. The switching architecture of the CAT21 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. Analog dimming and ED shutdown control is provided via a single input pin, CTR. Additional features include overload current protection and thermal shutdown. The device is available in the low profile 5 lead thin SOT23 package ideal for space constrained applications. Features ED Drive Current up to 35 ma Compatible with V and 2 V Standard Systems Handles Transients up to V Single Pin Control and Dimming Function Power Efficiency up to 9% Drives ED Strings of up to 32 V Open and Short ED Protection Parallel Configuration for Higher Output Current TSOT 23 5 lead Package These Devices are Pb Free, Halogen Free/BFR Free and are RoHS Compliant Applications V and 2 V ighting Systems Automotive and Aircraft ighting General ighting, High Brightness 35 ma EDs TSOT 23 TD SUFFIX CASE 19AE PIN CONNECTIONS AND MARKING DIAGRAMS (Top Views) CTR TFYM Device Package Shipping CAT21TD GT3 5 1 TF = Specific Device Code Y = Production Year (ast Digit) M = Production Month: (1 9, O, N, D) ORDERING INFORMATION * Plated Finish: NiPdAu 1 TSOT 23 TSOT 23 (Pb Free) SW 3,/ Tape & Reel 9 V C1.7 F CAT21 D C2 1 F 3 ma 1 k CTR SW 22 H D: ON Semiconductor MBR5 : Sumida CDRH6D26 22 See Table on page 6 for external component selection. Figure 1. Typical Application Circuit Semiconductor Components Industries, C, 215 September, 215 Rev. 9 1 Publication Order Number: CAT21/D

2 CAT21 Table 1. ABSOUTE MAXIMUM RATINGS Parameters Ratings Units, SW, CTR.3 to + V.3 to +5 V Switch SW peak current 1 A Storage Temperature Range 65 to + C Junction Temperature Range to +15 C ead Temperature 3 C Stresses exceeding those listed in the Maximum Ratings table may damage the device. If any of these limits are exceeded, device functionality should not be assumed, damage may occur and reliability may be affected. Table 2. RECOMMENDED OPERATING CONDITIONS Parameters Ratings Units voltage (Notes 1, 2) 6.5 to 36 (Note 1) V SW voltage to 36 V Ambient Temperature Range to +5 C ED Current 5 to 35 ma Switching Frequency 5 to 1 khz Functional operation above the stresses listed in the Recommended Operating Ranges is not implied. Extended exposure to stresses beyond the Recommended Operating Ranges limits may affect device reliability. 1. The pin voltage should be at least 3 V greater than the total sum of the ED forward voltages in order to operate at nominal ED current. 2. During power up, the slew rate of the input supply should be greater than 1 s for every 5 V increase of. Table 3. EECTRICA CHARACTERISTICS (V IN = 13 V, ambient temperature of 25 C (over recommended operating conditions unless otherwise specified)) Symbol Parameter Conditions Min Typ Max Units I Q Operating Supply Current on pin. 1 ma I SD Idle Mode Supply Current on pin CTR = 9 A V FB Pin Voltage 2 EDs with I ED = 3 ma V I ED Programmed ED Current = 33 k = 1 k =.25 k V CTR FU CTR Voltage for 1% Brightness V V CTR EN CTR Voltage to Enable EDs ED enable voltage threshold V V CTR SD CTR Voltage to Shutdown EDs ED disable voltage threshold..9 V I CTR CTR pin input bias V CTR = 3 V V CTR = V ma A R SW Switch On Resistance I SW = 3 ma T SD Thermal Shutdown 15 C T HYST Thermal Hysteresis 2 C Efficiency Typical Application Circuit 6 % Product parametric performance is indicated in the Electrical Characteristics for the listed test conditions, unless otherwise noted. Product performance may not be indicated by the Electrical Characteristics if operated under different conditions. 2

3 CAT21 TYPICA OPERATION CHARACTERISTICS (V IN = 13 V, I ED = 3 ma, = 22 H, C 1 =.7 F, C 2 = 1 F, T AMB = 25 C unless otherwise specified) 1. 2 QUIESCENT CURRENT (ma) IDE CURRENT ( A) Figure 2. Input Operating Supply Current Figure 3. Idle Mode Supply Current (CTR = V) CTR BIAS CURRENT ( A) VOTAGE (V) V IN = 13 V CTR VOTAGE (V) TEMPERATURE ( C) Figure. CTR Input Bias Current Figure 5. Voltage vs. Temperature VOTAGE (V) C C +5 C ED CURRENT (ma) CTR VOTAGE (V) (k ) Figure 6. Voltage vs. CTR Voltage Figure 7. ED Current vs. 3

4 CAT21 TYPICA OPERATION CHARACTERISTICS (V IN = 13 V, I ED = 3 ma, = 22 H, C 1 =.7 F, C 2 = 1 F, T AMB = 25 C unless otherwise specified) SWITCHING FREQUENCY (khz) ma ma 5 3 ma 3 ma 3 SWITCHING FREQUENCY (khz) Figure. Switching Frequency vs. Input Voltage (1 ED) Figure 9. Switching Frequency vs. Input Voltage (2 EDs) SWITCHING FREQUENCY (khz) ma 3 ma VIN = 13 V SW RESISTANCE ( ) TEMPERATURE ( C) Figure 1. Switching Frequency vs. Temperature Figure 11. Switch ON Resistance vs. Input Voltage ma EFFICIENCY (%) ma 3 ma EFFICIENCY (%) ma Figure. Efficiency vs. Input Voltage (1 ED) Figure 13. Efficiency vs. Input Voltage (2 EDs)

5 CAT21 TYPICA OPERATION CHARACTERISTICS (V IN = 13 V, I ED = 3 ma, = 22 H, C 1 =.7 F, C 2 = 1 F, T AMB = 25 C unless otherwise specified) 1 1 EFFICIENCY (%) EDs 1 ED ED CURRENT VARIATION (%) VIN = 13 V ED CURRENT (ma) TEMPERATURE ( C) Figure 1. Efficiency vs. ED Current Figure 15. ED Current Regulation vs. Temperature 35 3 V F = 3.3 V 3 ma 35 3 V F = 3.3 V 3 ma ED CURRENT (ma) V F = 3.1 V 15 ma ED CURRENT (ma) V F = 3.1 V 15 ma Figure. ED Current vs. Input Voltage (1 ED) Figure 17. ED Current vs. Input Voltage (2 EDs) SW 5V/div CTR 5V/div Inductor Current 2mA/ div ED Current 2mA/ div 2 s/div s/div Figure 1. Switching Waveforms Figure 19. CTR Power up 5

6 CAT21 TYPICA OPERATION CHARACTERISTICS (V IN = 13 V, I ED = 3 ma, = 22 H, C 1 =.7 F, C 2 = 1 F, T AMB = 25 C unless otherwise specified) Figure 2. Transient Response Figure 21. ine Transient Response (1 V to 13 V) External Component Selection Table provides the recommended external components and C2 that offer the best performance relative to the ED current accuracy, ED ripple current, switching frequency and component size. Table. EXTERNA COMPONENT SEECTION NOTE: 1 ED 2 EDs ED Current (ma) Inductor ( H) C2 Capacitor ( F) Inductor ( H) C2 Capacitor ( F) < arger C2 capacitor values allow to reduce further the ED ripple current if needed. Table 5. INDUCTOR SEECTION DEPENDING ON SUPPY VOTAGE Supply Voltage (V) Minimum Inductor ( H) <

7 CAT21 Table 6. PIN DESCRIPTION Pin Name Function 1 CTR Analog dimming control and shutdown pin. 2 Ground reference. 3 pin. A resistor connected between the pin and ground sets the average ED current. SW Interface to the inductor. 5 Supply voltage for the device. Pin Function is the supply input to the device. Typical current conduction into this pin is less than 1 ma and voltage transients of up to V can be applied. To ensure accurate ED current regulation, the voltage should be 3 V higher than the total forward voltage of the ED string. A bypass capacitor of.7 F or larger is recommended between and. CTR is the analog dimming and control input. An internal pull down current of 2 A allows the EDs to shutdown if CTR is left floating. Voltages of up to V can be safely handled by the CTR input pin. When the CTR voltage is less than.9 V (typ), the EDs will shutdown to zero current. When the CTR voltage is greater than about 2.6 V, full scale brightness is applied to the ED output. At voltages of less than around 2.6 V, the ED current is progressively dimmed until shutdown. For lamp replacement applications, or applications where operation in dropout mode is expected, it is recommended that the CTR pin voltage be derived from the ED cathode terminal. 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 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 ED or shorted ED fault conditions. pin is regulated at 1.2 V. A resistor connected between the pin and ground sets the ED full scale brightness current. The external resistance value and the CTR pin voltage determine the ED current during analog dimming. The pin must not be left floating. The highest recommended resistor value between and ground is 9 k. 7

8 CAT21 Simplified Block Diagram V/2 V CTR 3 k 2 A 7 V EN PWM Controller OFF Time Control SW 1.2 V Reference + EN ON Time Control 1.2 V R 2 1 Figure 22. CAT21 Simplified Block Diagram Basic Operation The CAT21 is a high efficiency step down regulator designed to drive series connected high power EDs. ED strings with total forward voltages of up to 32 V can be driven with bias currents of up to 35 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 ED current which is equal to half of the peak switching current. ED Pin Current The ED current is set by the external resistor connected to the regulated output of the pin. An overall current gain ratio of approximately 2.5 A/mA exists between the average ED current and the current, hence the following equation can be used to calculate the ED current. ED Current (A) 2.5 V (V) R SET (k ) Table 7 lists the various ED currents and the associated resistors. Table 7. RESISTOR SEECTION ED Current (A) (k )

9 CAT21 APPICATION INFORMATION Input Voltage Range The minimum supply voltage required to maintain adequate regulation is set by the cathode terminal voltage of the ED string (i.e., the voltage minus the ED string voltage). When the ED 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 CTR input be used to sense the ED cathode voltage. The CTR pin can either be tied directly to the cathode terminal (for amp Replacement) or connected via a pass transistor for PWM lighting applications. Figure 23 shows the regulation performance obtained in dropout, when the CTR pin is configured to sense the ED cathode voltage. ED CURRENT [ma] ma 15 ma CTR VOTAGE [V] Figure 23. Dropout Configured ED Current (as shown in Typical Application on page 1) Inductor Selection A 22 H minimum inductor value is required to provide suitable switching frequency across a wide range of input supply values. For ED current of 15 ma or less, a 33 H or 7 H inductor is more suitable. Inductor values below 22 H should not be used. An inductor with at least 7 ma current rating must be used. Minor improvements in efficiency can be achieved by selecting inductors with lower series resistance. Table. SUMIDA INDUCTORS Part Number ( H) I Rated (A) ED Current (A) Capacitor Selection A 1 F ceramic capacitor C2 across the ED(s) keeps the ED ripple current within ±15% of nominal for most applications. If needed, a larger capacitor can be used to further reduce the ED current ripple. Any resistance in series with the ED (.5 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 ED fault conditions. The capacitor value is independent of the switching frequency or the overall efficiency. A.7 F 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. Schottky Diode 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 ED 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 MBR5 ( V, 5 ma rated) is recommended. Schottky diodes rated at ma (or higher) continuous current are fine for most applications. NOTE: Schottky diodes with extremely low forward voltages (V F ) are not recommended, as they may cause an increase in the ED current. Dimming Methods Two methods for PWM dimming control on the EDs 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 pin and connected in parallel with. PWM on CTR Pin A PWM signal from a microprocessor can be used for dimming the EDs when tied to the CTR 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 CTR pin is between 1 Hz and 2 khz. CDRH6D CDRH6D CDRH6D CDRH6D Figure 2. PWM at 1 khz on CTR Pin 9

10 CAT21 ED CURRENT [ma] V 5 V V 1.7 F PWM control 6 DUTY CYCE [%] 2 Figure 25. ED Current vs. Duty Cycle C1 1 k CAT21 R 1 k CTR SW R5 7 k C2 1 F Figure 26. Circuit for PWM on CTR D 22 H R2 1 k Q1 NPN PWM on Pin Another dimming method is to place in parallel to another resistor with a FET in series, as shown on Figure 27. sets the minimum ED current corresponding to % duty cycle. The combined resistor of and Rmax sets the maximum ED current corresponding to 1% duty cycle. 13 V Rmax PWM control C1.7 F OFF ON CAT21 CTR SW C2 1 F Figure 27. Circuit for PWM on D 22 H R2 1 k Q1 NPN A resistor value for of less than 9 k is recommended to provide better accuracy. Operation from High Supply Voltage Above 1 V For operation from a supply voltage above 1 V, it is recommended to have a slew rate of 1 s or more for every 5 V increase in supply. When using a high supply voltage of 2 V, a 1 or 2 resistor in series with the supply, as shown on Figure 2, is recommended to limit the slew rate of the supply voltage. A.7 F minimum ceramic capacitor is placed between the 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 CAT21 driver. 2 V R3 1 C1.7 F 1 k CAT21 CTR SW D1 C2.7 F 1 k Figure 2. 2 V Application with 5 EDs 33 H 3 ma Operation from High Supply Voltage of 36 V When powering from a high supply voltage of 36 V, a 2 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 H or higher. 36 V R3 2 C1.7 F 1 k CAT21 CTR SW R2 D1 C2 2.2 F 1 k Figure V Application with 6 EDs 7 H 3 ma Parallel Configuration for Driving EDs Beyond 35 ma Several CAT21 devices can be connected in parallel for driving EDs with current in excess of 35 ma. The CAT21 driver circuits are connected to the same ED cathode. Figure 3 shows the application schematic for driving 1 A into one ED with three CAT21 connected in parallel. Each CAT21 is driving the ED with a current set by its resistor. The resulting ED current is equal to the sum of each driver current. 1

11 CAT21 VIN R5 1 C1.7 μf.3 kω U1 CAT21 CTR SW D μh C 1 μf 1 A R 1 kω C2.7 μf U2 D2 CAT21 R2.3 kω 2 CTR SW 22 μh C3.7 μf R3.3 kω U3 CAT21 CTR SW D μh Figure 31. Open ED Mode Board ayout 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 pin and the Schottky diode cathode. The CAT21 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 EDs are connected by two wires tied to both sides of the output capacitor C2. The EDs can be located away from the driver if needed. Figure 3. Three CAT21 in Parallel for 1 A ED Open ED Behavior If the EDs are not connected, the CAT21 stops switching and draws very little current. At power up with no load connected, the capacitor C2 is charged up by the CAT21. As soon as the bottom side of the capacitor (C2 ) reaches volt, as shown on Figure 31, the CAT21 stops switching and remains in the idle mode only drawing about. ma current from the supply. Figure 32. Recommended PCB ayout In order to further reduce the ripple on the supply rail, an optional Pi style filter (C C) can be used. A 1 H inductor rated to the maximum supply current can be used. 11

12 CAT21 PACKAGE DIMENSIONS TSOT 23, 5 EAD CASE 19AE 1 ISSUE O e D SYMBO A A1 MIN NOM MAX A b.3.5 c E1 E D E 2.9 BSC 2. BSC E1 1.6 BSC e.95 TYP REF 2.25 BSC TOP VIEW θ º º A2 A b A1 1 c 2 SIDE VIEW END VIEW Notes: (1) All dimensions are in millimeters. Angles in degrees. (2) Complies with JEDEC MO All packages are RoHS compliant (ead free, Halogen free).. The standard plated finish is NiPdAu on all pins. 5. For additional package and temperature options, please contact your nearest ON Semiconductor Sales office. 6. For information on tape and reel specifications, including part orientation and tape sizes, please refer to our Tape and Reel Packaging Specifications Brochure, BRD11/D. ON Semiconductor and the are registered trademarks of Semiconductor Components Industries, C (SCIC) or its subsidiaries in the United States and/or other countries. SCIC owns the rights to a number of patents, trademarks, copyrights, trade secrets, and other intellectual property. A listing of SCIC s product/patent coverage may be accessed at /site/pdf/patent Marking.pdf. SCIC reserves the right to make changes without further notice to any products herein. SCIC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCIC 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 SCIC 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. SCIC does not convey any license under its patent rights nor the rights of others. SCIC 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 SCIC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCIC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCIC 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 SCIC was negligent regarding the design or manufacture of the part. SCIC is an Equal Opportunity/Affirmative Action Employer. This literature is subject to all applicable copyright laws and is not for resale in any manner. PUBICATION ORDERING INFORMATION ITERATURE FUFIMENT: iterature Distribution Center for ON Semiconductor E. 32nd Pkwy, Aurora, Colorado 11 USA Phone: or 3 36 Toll Free USA/Canada Fax: or Toll Free USA/Canada orderlit@onsemi.com N. American Technical Support: Toll Free USA/Canada Europe, Middle East and Africa Technical Support: Phone: Japan Customer Focus Center Phone: ON Semiconductor Website: Order iterature: For additional information, please contact your local Sales Representative CAT21/D