WHITE LED STEP-UP CONVERTER General Description. Features. Applications

Transcription

1 General Description The is an inductor-based DC/DC converter designed to drive up to six white LEDs in series for backlight. Only one feedback resistor is needed to control the LED current and obtain satisfied brightness. A constant frequency 1.2MHz PWM control scheme is employed in this IC, which means the tiny external components can be used. In fact, 1mm tall inductor and 0.22µF output capacitor for the typical application is very appropriate. Additionally, the schottky diode in boost circuit is integrated in this chip. also provide a disable port to ease its use for different systems. The over output voltage protection is equipped in. When any LED is broken or in other abnormal conditions, the output voltage will be clamped to 30V. The is available in standard SOT-23-6 package. Features Inherently Uniform LED Current High Efficiency: 83% Typical No Need for Extra Schottky Diode Over Output Voltage Protection Drives 2 to 6 LEDs Fast 1.2MHz Switching Frequency Uses Tiny 1mm Tall Inductor Requires Only 0.22µF Output Capacitor Applications Cellular Phones Digital Cameras LCD modules GPS Receivers PDAs, Handheld Computers SOT-23-6 Figure 1. Package Type of 1

2 Pin Configuration K Package (SOT-23-6) Pin 1 Mark V OUT 1 6 SW GND 2 FB 3 4 CTRL Figure 2. Pin Configuration of (Top View) Pin Description Pin Number Pin Name Function 1 V OUT Output Pin. Connected to the cathode of internal schottky diode 2 GND Ground Pin 3 FB Voltage Feedback. Reference voltage is 200mV 4 CTRL Shutdown and Dimming Pin. Connect to 1.8V or higher to enable device; Connect to 0mV or less to disable device; Connect to a voltage between 1.8V and 0mV to achieve linear dimming Input Supply Pin. Must be locally bypassed 6 SW Switch Pin. Connect external inductor 2

3 Functional Block Diagram FB SW V OUT V REF 1.2 V 200 mv A1 A2 R S Q DRIVER Q1 OVP COMPARATOR CTRL 4 Σ RAMP GENERATOR 2 GND 1.2 MHz OSCILLATOR Figure 3. Functional Block Diagram of Ordering Information - Circuit Type E1: RoHS Package K: SOT-23-6 TR: Tape and Reel Package Temperature Range Part Number Marking ID Packing Type SOT to 8 o C KTR-E1 E9T Tape & Reel BCD Semiconductor's products as designated with "E1" suffix in the part number are RoHS compliant. 3

4 Absolute Maximum Ratings (Note 1) Parameter Symbol Value Unit Input Voltage 20 V SW Voltage 38 V FB Voltage 20 V CTRL Voltage 20 V Thermal Resistance (Junction to Atmosphere, no Heat sink) θ JA 26 o C/W Operating Junction Temperature 10 o C Storage Temperature Range T STG -6 to 10 o C Lead Temperature (Soldering, 10sec) T LEAD 260 o C ESD (Machine Model) 20 V ESD (Human Body Model) 2000 V Note 1: Stresses greater than those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated under "Recommended Operating Conditions" is not implied. Exposure to "Absolute Maximum Ratings" for extended periods may affect device reliability. Recommended Operating Conditions Parameter Symbol Min Max Unit Operating Temperature Range T OP o C Input Voltage V CTRL Voltage V CTRL 16 V 4

5 Electrical Characteristics ( =3V, V CTRL =3V, T A =2 o C, unless otherwise specified.) Parameter Symbol Conditions Min Typ Max Unit Minimum Operating Voltage (min) 2. Maximum Operating Voltage (max) 16 V Feedback Voltage V FB I OUT =20mA, 4 LEDs, T A =-40 o C to 8 o C mv FB Pin Bias Current I FB na Supply Current I CC V FB =, Not Switching ma Supply Current I Q V CTRL =0V µa Switching Frequency f MHz Maximum Duty Cycle D MAX % Switch Current Limit (Note 2) I LIMIT T A =2 o C, D=40% 60 ma T A =2 o C, D=80% 46 Switch V CE Saturation Voltage V CESAT I SW =20mA 300 mv Switch Leakage Current V SW =V 0.01 µa CTRL Pin Voltage V CTRL High 1.8 Low 0.0 V CTRL Pin Bias Current I CTRL T A =8 o C µa T A =-40 o C Schottky Forward Drop V DROP I D =10mA 0.7 V Schottky Leakage Current V R =2V 4 V R =30V 90 µa Thermal Resistance (Junction to Case) θ JC o C/W Note 2: The Switch Current Limit is related to Duty Cycle. Please refer to Figure 16 for detail.

6 Typical Performance Characteristics (V F of WLED is I F =20mA, unless otherwise noted ) Efficiency (%) Efficiency (%) =3.6V, I OUT =20mA, 4 LEDs C IN =1µF, C OUT =0.22µF, L=22µH 81 4 LEDs, I OUT =20mA, T A =2 o C C IN =1µF, C OUT =0.22µF, L=22µH Junction Temperature ( o C) Input Voltage (V) Figure 4. Efficiency vs. Junction Temperature Figure. Efficiency vs. Input Voltage Efficiency (%) =3.6V, I OUT =20mA, T A =2 o C C IN =1µF, C OUT =0.22µF, L=22µH Schottky Forward Current (ma) LEDs (pcs) Schottky Forward Drop (mv) Figure 6. Efficiency vs. LED's Number Figure 7. Schottky Forward Current vs. Schorttky Forward Drop 6

7 Typical Performance Characteristics (Continued) (V F of WLED is I F =20mA, unless otherwise noted ) Shutdown Quiescent Current (µa) Supply Current (ma) o C 100 o C -0 o C Input Voltage (V) Input Voltage (V) Figure 8. Shutdown Quiescent Current vs. Input Voltage Figure 9. Supply Current vs. Input Voltage Output Clamp Voltage (V) Input Current in Ouput Open Circuit (ma) Input Voltage (V) Input Voltage (V) Figure 10. Output Clamp Voltage vs. Input Voltage Figure 11. Input Current in Output Open Circuit vs. Input Voltage 7

8 Typical Performance Characteristics (Continued) (V F of WLED is I F =20mA, unless otherwise noted ) Switching Frequency (MHz) Feedback Voltage (mv) Junction Temperature ( o C) Junction Temperature ( o C) Figure 12. Switching Frequency Figure 13. Feedback Voltage vs. Junction Temperature vs. Junction Temperature Schottky Forward Drop (V) Schottky Leakage Current (ua) V R =10V V R =16V V R =2V 0.62 I D =10mA Junction Temperature ( o C) Junction Temperature ( o C) Figure 14. Schottky Forward Drop vs. Junction Temperature Figure 1. Schottky Leackage Current vs. Junction Temperature 8

9 Typical Performance Characteristics (Continued) (V F of WLED is I F =20mA, unless otherwise noted ) Switching Current Limit (ma) o C 2 o C 100 o C Switch Saturation Voltage (mv) Duty Cycle (%) Switch Current (ma) Figure 16. Switch Current Limit vs. Duty Cycle Figure 17. Switch Saturation Voltage vs. Switch Current Feedback Voltage (mv) CTRL Pin Voltage (V) Figure 18. Feedback Voltage vs. CTRL Pin Voltage 9

10 Typical Application 3V 22µΗ 6 1 Control Signal 1µF 4 SW V OUT CTRL GND 2 FB 3 10Ω 0.22µF a. Four White LEDs Driver 3V 22µΗ 6 1 Control Signal 1µF 4 SW V OUT CTRL GND 2 FB 3 10Ω 0.22µF b. Five White LEDs Driver 10

11 Typical Application (Continued) 3V 22µΗ 6 1 Control Signal 1µF 4 SW V OUT CTRL GND 2 FB 3 10Ω 0.22µF c. Six White LEDs Driver C: XR or X7R Dielectric L: SUMIDA CDRHD28R-220NC or Equivalent All these circuits can work in full temperature Figure 19. Typical White LED Drivers 11

12 Mechanical Dimensions SOT-23-6 Unit: mm(inch) 0.300(0.012) 0.00(0.020) 2.820(0.111) 3.100(0.122) (0.008) (0.012) 0.600(0.024) 2.60(0.104) 3.000(0.118) Pin 1 Mark 1.00(0.09) 1.700(0.067) (0.028)REF 0.90(0.037)TYP 1.800(0.071) 2.000(0.079) 0.000(0.000) 0.10(0.006) 0.100(0.004) 0.200(0.008) 0.900(0.03) 1.300(0.01) 1.40(0.07) MAX 12

13 Mounting Pad Layout SOT-23-6 E E Y G Z X Dimensions Z (mm)/(inch) G (mm)/(inch) X (mm)/(inch) Y (mm)/(inch) E (mm)/(inch) Value 3.600/ / / / /

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