RT9271 Preliminary White LED Step-Up Converter in Tiny Package General Description Features The RT9271 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive one to four LEDs in series from a Li-Ion cell. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The RT9271 switches at 1.1 MHz, allowing the use of tiny external components. The input and output capacitor can be as small as 1uF, saving space and cost versus alternative solutions. A low 0.25V feedback voltage minimizes power loss in the current setting resistor for better efficiency. The RT9271 is available in low profile SOT26 package. • • • • • • • • • Ordering Information RT9271 Package Type E : SOT-26 Operating Temperature Range C : Commercial Standard Marking Information Inherently Matched LED Current High Efficiency: 85% Typical Drives Up to Four LEDs from 2.8V Supply 20V Internal Switch Fast 1.1 MHz Switching Frequency Uses Tiny 1 mm Tall Inductors Requires Only 1uF Output Capacitor Low Profile SOT-26 Package Optional 15V Over Voltage Protection Applications • • • • • Mobile Phone Digital Still Camera PDAs, Handheld Computers MP3 Players GPS Receivers Pin Configurations Pin Configuration Part Number RT9271CE (Plastic SOT-26) LX 1 6 VCC GND 2 5 OVP FB 3 4 CE For marking information, contact our sales representative directly or through a RichTek distributor located in your area, otherwise visit our website for detail. Pin Assignment Pin Name 1 LX 2 GND 3 FB Feedback Pin. Reference voltage is 0.25V. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RFB = 0.25/ILED 4 CE Chip Enable Pin. Connect to 1.4V or higher to enable device, 0.4V or less to disable device. 5 OVP Over Voltage Protection Pin. Voltage sensing input to trigger the function of over voltage protection, the trip point is 15.5V. Leave it unconnected to disable this function. 6 VCC Input Voltage Pin. Must be locally bypass with 1uF capacitor to GND. DS9271-01 Function Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to reduce EMI Ground Pin. Connect directly to local ground plane. July 2003 www.richtek.com 1 RT9271 Preliminary Typical Application Circuit Vin 2.4 to 3.2V C1 1uF LX 10uH VCC C3 1uF LX D2 OVP CE Dimming Control D1 SS12 GND FB R2 12Ω Fig. 1 RT9271 Drivers 1 WLED Application Circuit Vin 2.4 to 5V C1 1uF LX 4.7uH Dimming Control D2 C3 1uF LX VCC CE D1 SS12 D3 OVP GND FB R2 12Ω Fig. 2 RT9271 Drivers 2 Series WLEDs Application Circuit Vin 2.4 to 6V C1 1uF LX 6.8uH D1 SS12 D2 VCC CE Dimming Control GND LX D3 C3 1uF D4 OVP FB R2 12Ω Fig. 3 RT9271 Drivers 3 Series WLEDs Application Circuit www.richtek.com 2 DS9271-01 July 2003 RT9271 Preliminary C1 1uF Vin 2.8 to 6V LX 4.7uH D1 SS12 D2 VCC D4 OVP CE Dimming Control D3 C3 1uF LX GND D5 FB R2 12Ω Fig. 4 RT9271 Drivers 4 Series WLEDs Application Circuit Note : 1. D1 is Schottky diode (SS12). 2. D2 ~ D5 are the WLED (HT-S91CW-DT) of HARVATEK. 3. LX is the SH4018 series of ABC TAIWAN ELECTRONICS CORP. Function Block Diagram OVP SW 15V A1 + FB - COMPARATOR A2 R + S V REF 0.25V CHIP ENABLE Q M1 + CE VCC DRIVER GND RAMP GENERATOR 1.1MHz OSCILLATOR DS9271-01 July 2003 www.richtek.com 3 RT9271 Preliminary Absolute Maximum Ratings −0.3V to 7V −0.3V to 21V −0.3V to 21V 0°C to 70°C 0°C to 125°C −65°C to 150°C Input Supply Voltage SW The Other Pins Operating Temperature Range Junction Temperature Range Storage Temperature Range Electrical Characteristics (VCC = 3.6V, TA = 25°C, Unless Otherwise specification) Parameter Symbol Test Condition Min Typ Max Units 6 V System Supply Input Operation Voltage Range VCC Under Voltage Lock Out UVLO 2.4 2.2 Maximum Output Voltage Supply Current ICC1 VCC=6V, Continuously Switching Quiescent Current ICC2 VCC=6V, FB=1.3V, No Switching Shut Down Current ICC3 VCC=6V, VCE<0.4V V 20 V 2 mA 90 µA 1 µA 1.3 MHz Oscillator Operation Frequency FOSC 0.9 1.1 Maximum Duty Cycle Dmax 85 90 0.237 0.25 % Reference Voltage Feedback Voltage VFB 0.263 V MOSFET On Resistance of MOSFET Rds(on) Current Limitation Imax1 Current Limit Imax2 0.75 Ω Normal Operation 800 mA Start up Condition 500 mA 0.8 V Control and Protection Shut Down Voltage VCE1 Enable Voltage VCE2 CE Pin Pull Low Current ICE OVP Threshold OVP 0.4 0.8 1.4 4 14.5 15.5 V µA 20.0 V Note: Floating the OVP pin to disable OVP function www.richtek.com 4 DS9271-01 July 2003 RT9271 Preliminary Typical Operating Characteristics Efficiency vs. Vin (Driving 1 WLED) 88 87 IO = 20mA 86 IO = 15mA 85 84 83 TA = 25°C 88 87 IO = 20mA 86 85 84 83 IO = 15mA 82 81 80 82 2 2.5 3 3.5 2 4 3 4 87 86 85 IO = 20mA 84 83 IO = 15mA 82 81 86 85 TA = 25°C IO = 20mA 84 Efficiency (%) Efficiency (%) 88 Refer to Application Circuit Fig. 3 TA = 25°C 89 6 Efficiency vs. Vin (Driving 4 WLEDs) Efficiency vs. Vin (Driving 3 WLEDs) 90 5 Vin (V) Vin (V) 83 IO = 15mA 82 81 80 79 78 77 76 80 2 3 4 5 6 6.5 2 3 4 Frequency vs. Vin 1.3 6 6.5 VFB vs. Temperature 260 Driving 3 WLEDs TA = 25°C 1.2 5 Vin (V) Vin (V) Driving 3 WLEDs VIN = 3.6V 255 1.1 250 VFB (mV) Frequency (MHz)1 Refer to Application Circuit Fig. 2 89 89 Refer to Application Circuit Fig. 4 Efficiency (%) 90 90 Efficiency (%) TA = 25°C 91 Efficiency vs. Vin (Driving 2 WLEDs) Refer to Application Circuit Fig. 1 92 1 0.9 0.8 245 240 235 0.7 230 2 3 4 Vin (V) DS9271-01 July 2003 5 6 6.5 0 10 20 30 40 50 60 70 Temperature(°C) www.richtek.com 5 RT9271 Preliminary VIN vs. Temperature VIN =2.4V 4 WLEDs VIN (V) 2.8 VOUT (AC) 2.6 2.4 VLX 3 WLEDs 2.2 IIN Minimum Input Voltage vs. Temperature for Delivering Full Brightness 2 20 30 40 50 60 70 100mA/Div Refer to Application Circuit Fig. 1 Stability for Driving 1 WLED 3 Time (500 ns/Div) Temperature(˚C) Stability for Driving 1 WLED VLX IIN VIN =2.4V VOUT (AC) VLX IIN 100mA/Div 100mA/Div Stability for Driving 2 WLEDs Stability for Driving 2 WLEDs VIN =3.6V VOUT (AC) VLX IIN 100mA/Div Time (500 ns/Div) www.richtek.com Refer to Application Circuit Fig. 2 Time (500 ns/Div) Refer to Application Circuit Fig. 2 Time (500 ns/Div) Refer to Application Circuit Fig. 2 Refer to Application Circuit Fig. 1 VIN =3.2V VOUT (AC) 6 Stability for Driving 2 WLEDs VIN =5.2V VOUT (AC) VLX IIN 100mA/Div Time (500 ns/Div) DS9271-01 July 2003 Preliminary IIN 100mA/Div VIN =3.6V VOUT (AC) VLX IIN 100mA/Div Time (500 ns/Div) Stability for Driving 3 WLEDs Stability for Driving 4 WLEDs Refer to Application Circuit Fig. 3 Time (500 ns/Div) VIN =6V VOUT (AC) VLX IIN VIN =2.4V VOUT (AC) VLX IIN 100mA/Div Refer to Application Circuit Fig. 4 VLX Refer to Application Circuit Fig. 3 VOUT (AC) Refer to Application Circuit Fig. 3 Stability for Driving 3 WLEDs Stability for Driving 3 WLEDs VIN =2.4V RT9271 Time (500 ns/Div) Stability for Driving 4 WLEDs Stability for Driving 4 WLEDs VIN =3.6V VOUT (AC) VLX IIN 100mA/Div Time (500 ns/Div) DS9271-01 July 2003 Refer to Application Circuit Fig. 4 Time (500 ns/Div) VIN =6V VOUT (AC) VLX IIN 100mA/Div Refer to Application Circuit Fig. 4 100mA/Div Time (500 ns/Div) www.richtek.com 7 RT9271 Preliminary Inrush Current for Driving 1 WLED VOUT IIN(max) = 730mA IIN VCE =2V VIN =3.6V IIN(max) = 630mA IIN VOUT Time (10 us/Div) Inrush Current for Driving 3 WLEDs Inrush Current for Driving 4 WLEDs Frequency = 200Hz VCE =2V VIN =3.6V IIN(max) = 650mA IIN VOUT Refer to Application Circuit Fig. 3 Time (20 us/Div) Time (20 us/Div) Frequency = 200Hz VCE =2V VIN =3.6V IIN IIN(max) = 750mA VOUT Refer to Application Circuit Fig. 2 VIN =3V Frequency = 200Hz Refer to Application Circuit Fig. 4 VCE =2V Refer to Application Circuit Fig. 1 Frequency = 200Hz Inrush Current for Driving 2 WLEDs Time (20 us/Div) Refer to Application Circuit Fig. 4 Dimming Control for Driving 4 WLEDs VCE VLX VOUT VIN =3.6V Time (500 ns/Div) www.richtek.com 8 DS9271-01 July 2003 RT9271 Preliminary Application Note LED Current Control The LED current is controlled by the feedback resistor (R2 in Application Circuit). The feedback reference is 0.25V. The LED current is 0.25V/R2. In order to have accurate LED current, precision resistors are preferred (1% is recommended). The formula and table for R2 selection are shown below. Board Layout Example (2-Layer EVB Board) (Refer to EVB Circuit) R2 = 0.25V/ILED R2 Resistor Value Selection ILED (mA) R2 (Ω) 5 49.9 10 24.9 12 21 15 16.5 20 12.4 - Top Layer – Recommended Inductance (for Li-Ion cell) Condition Inductance (µH) 1 WLED 10 2 WLEDs 4.7 3 WLEDs 6.8 4 WLEDs 4.7 - Bottom Layer - Layout Guide • • S1 Vin + A full GND plane without gap break. VCC to GND noise bypass – Short and wide connection for the 1µF MLCC capacitor between Pin6 and Pin2. • Minimized LX node copper area to reduce EMI. • Minimized FB node copper area and keep far away from noise sources. R1 C5 C1 D1 VCC LX OVP CE S3 D2 L1 C2 RT9271 GND C3 D3 D4 C4 D5 S2 FB R2 EVB Circuit DS9271-01 July 2003 www.richtek.com 9 RT9271 Preliminary Package Information H D L C B b A A1 e Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 0.889 1.295 0.035 0.051 A1 -- 0.152 -- 0.006 B 1.397 1.803 0.055 0.071 b 0.356 0.559 0.014 0.022 C 2.591 2.997 0.102 0.118 D 2.692 3.099 0.106 0.122 e 0.838 1.041 0.033 0.041 H 0.102 0.254 0.004 0.010 L 0.356 0.610 0.014 0.024 SOT- 26 Surface Mount Package www.richtek.com 10 DS9271-01 July 2003 RT9271 DS9271-01 July 2003 Preliminary www.richtek.com 11 RT9271 Preliminary RICHTEK TECHNOLOGY CORP. RICHTEK TECHNOLOGY CORP. Headquarter Taipei Office (Marketing) 5F, No. 20, Tai Yuan Road, Chupei City 8F-1, No. 137, Lane 235, Paochiao Road, Hsintien City Hsinchu, Taiwan, R.O.C. Taipei County, Taiwan, R.O.C. Tel: (8863)5526789 Fax: (8863)5526611 Tel: (8862)89191466 Fax: (8862)89191465 Email: [email protected] www.richtek.com 12 DS9271-01 July 2003