 |
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
|
| If you can't view the Datasheet, Please click here to try to view without PDF Reader . |
|
|
| Datasheet File OCR Text: |
| UTC L1937 WHITE LED STEP-UP CONVERTER LINEAR INTEGRATED CIRCUIT 2 1 DESCRIPTION The UTC L1937 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive two, three or 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 UTC LT1937 switches at 1.2MHz, allowing the use of tiny external components. The output capacitor can be as small as 0.22 F, saving space and cost versus alternative solutions. A low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. 3 5 4 SOT-25 1 FEATURES * Inherently Matched LED Current * High Efficiency: 84% Typical * Drives Up to Four LEDs from a 3.2V Supply * Drives Up to Six LEDs from a 5V Supply * 36V Rugged Bipolar Switch * Fast 1.2MHz Switching Frequency * Uses Tiny 1mm Tall Inductors * Requires Only 0.22 F Output Capacitor SOT-363 *Pb-free plating product number: L1937L APPLICATIONS * Marking code: LTCG * Cellular Phones * PDAs, Handheld Computers * Digital Cameras * MP3 Players * GPS Receivers PIN FUNCTION PIN NO. PIN NO. PIN NAME (SOT-25) (SOT-363). 1 2 3 4 5 6 5 Switch Ground Feedback Shutdown Input Supply Ground SYMBOL SW GND FB FUNCTION Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. Connect directly to local ground plane. Reference voltage is 95mV. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: RFB = 95mV/ILED Connect to 1.5V or higher to enable device;0.4V or less to disable device. Input Supply Pin. Must be locally bypassed. Connect to Pin 2 and to local ground plane SHDN VIN GND UTC UNISONIC TECHNOLOGIES CO., LTD. 1 QW-R103-021,A UTC L1937 BLOCK DIAGRAM VIN 5 LINEAR INTEGRATED CIRCUIT FB 3 COMPARATOR VREF 1.25V 95mV SW 1 ( PIN 6 FOR SOT-363 PACKAGE ) A1 + Rc Cc A2 + DRIVER R S Q Q1 + RAMP GENERATOR 0.2 SHDN 4 SHUTDOWN 2 1.2MHz OSCILIATOR GND ( PINS 2 AND 5 FOR SOT-363 PACKAGE ) ABSOLUTE MAXIMUM RATINGS PARAMETER Input Voltage SW Voltage FB Voltage SHDN Voltage Operating Temperature Storage Temperature Maximum Junction Temperature Lead Temperature (Soldering, 10 sec) SYMBOL VIN VSW VFB VSHDN Topr Tstg Tj TLead RATINGS 10 36 10 10 -40 ~ +85 -65 ~ +150 125 300 UNIT V V V V ELECTRICAL CHARACTERISTICS (Ta=25 PARAMETER Operating Voltage Feedback Voltage FB Pin Bias Current Supply Current Switching Frequency Maximum Duty Cycle Switch Current Limit Switch VCESAT Switch Leakage Current SHDN Voltage High SHDN Voltage Low SHDN Pin Bias Current , VIN=3V, VSHDN=3V, unless otherwise noted.) SYMBOL VIN VFB IFB Icc TEST CONDITIONS ISW=100mA,Duty Cycle=66% MIN 86 10 TYP MAX UNIT 95 45 1.9 0.1 1.2 90 320 350 0.01 10 104 100 2.5 1.0 1.6 V mV nA mA A MHz % mA mV A V V A SHDN=0V fosc DC ISW VCESAT(SW) ISW=250mA ISW(OFF) VSW=5V VIH VIL ISHDN 0.8 85 5 0.4 1.5 65 UTC UNISONIC TECHNOLOGIES CO., LTD. 2 QW-R103-021,A UTC L1937 TYPICAL APPLICATIONS LINEAR INTEGRATED CIRCUIT Conversion Efficiency VIN 3V ~ 5V L1 22 F C1 1F VIN SW 90 D1 C2 0.22 F EFFICIENCY(%) 15mA 85 LED 1 LED 2 LED 3 80 VIN=3V 75 VIN=3.6V OFF ON SHDN GND FB R1 6.34 70 Li-Ion Powered Driver for Three White LEDs 65 60 0 5 10 LED CURRENT (mA) 15 20 Two LED Efficiency 86 L 22 H VIN 3V ~ 5V CIN 1F VIN 84 82 VIN=3V EFFICIENCY(%) 80 78 76 74 72 VIN=3.6V D VDC DIMMING SW 90k 5k COUT 1F SHDN GND FB R1 2 Li-Ion to Two White LEDs 70 0 10 20 LED CURRENT (mA) 30 40 UTC UNISONIC TECHNOLOGIES CO., LTD. 3 QW-R103-021,A UTC L1937 LINEAR INTEGRATED CIRCUIT Three LED Efficiency 90 L 22 H VIN 3V ~ 5V D VDC DIMMING COUT 0.22 F EFFICIENCY(%) 85 CIN 1F VIN 80 VIN=3V 75 VIN=3.6V SW 90k 5k R1 4 UTC LT1937 SHDN GND FB 70 65 Li-Ion to Three White LEDs 60 0 5 10 LED CURRENT (mA) 15 20 Five LED Efficiency L 22 H VIN 3V ~ 5V CIN 1F VIN SW 90k 5k SHDN GND FB R1 4 85 D COUT 0.22 F EFFICIENCY(%) VDC DIMMING 80 VIN=3V 75 VIN=3.6V 70 Li-Ion to Five White LEDs 65 0 2 4 6 8 10 12 LOAD CURRENT (mA) UTC UNISONIC TECHNOLOGIES CO., LTD. 4 QW-R103-021,A UTC L1937 L 22 H CIN 1F VIN LINEAR INTEGRATED CIRCUIT Seven LED Efficiency 85 D COUT 0.22 F EFFICIENCY(%) 80 VIN 5V VDC DIMMING SW 90k SHDN GND FB 5k R1 4 75 70 5V to Seven White LEDs 65 0 5 10 15 LOAD CURRENT (mA) Four LED Efficiency 85 L 22 H VIN 3V ~ 5V CIN 1F VIN SW 90k 5k R1 4 D VDC DIMMING COUT 0.22 F EFFICIENCY(%) 80 VIN=3V VIN=3.6V 75 SHDN GND FB 70 Li-Ion to Four White LEDs 65 0 5 10 LOAD CURRENT (mA) 15 20 UTC UNISONIC TECHNOLOGIES CO., LTD. 5 QW-R103-021,A UTC L1937 2.2 2.0 100 LINEAR INTEGRATED CIRCUIT Quiescent Current -50 350 SHDN PIN BIAS CURRENT ( A) 25 300 SHDN=10V 250 200 150 SHDN=3.6V 100 50 SHDN=2.7V 0 -50 SHDN=3V 400 TYPICAL PERFORMANCE CHARACTERISTICS SHDN Pin Bias Current 1.8 1.6 1.4 IQ (mA) 1.2 1.0 0.8 0.6 0.4 0.2 0 0 2 4 VIN (V) 6 8 10 -25 0 25 50 ) 75 100 TEMPERATURE ( Switching Frequency 1.4 1.2 SWITCHING FREQUENCY (MHz) FEEDBACK CURRENT (nA) 60 Feedback Bias Current 50 1.0 40 0.8 0.6 0.4 30 20 0.2 10 0 -50 -25 0 25 50 ) 75 100 0 -50 -25 0 25 50 ) 75 100 TEMPERATURE ( TEMPERATURE ( Efficiency vs Temperature 85 VIN=3.6V 3 LEDs ILED=20mA 84 CURRENT LIMIT (mA) 250 300 350 Current Limit vs Duty Cycle Efficiency(%) 83 ILED=15mA 200 150 82 ILED=10mA 100 50 81 80 -50 0 0 TEMPERATURE ( 50 ) 100 0 20 40 60 80 DUTY CYCLE (%) 100 UTC UNISONIC TECHNOLOGIES CO., LTD. 6 QW-R103-021,A UTC L1937 LINEAR INTEGRATED CIRCUIT UTC assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all UTC products described or contained herein. UTC products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. UTC UNISONIC TECHNOLOGIES CO., LTD. 7 QW-R103-021,A |
Price & Availability of L1937
 |
|
|
|
|
All Rights Reserved © IC-ON-LINE 2003 - 2022 |
| [Add Bookmark] [Contact Us] [Link exchange] [Privacy policy] |
|
Mirror Sites : [www.datasheet.hk]
[www.maxim4u.com] [www.ic-on-line.cn]
[www.ic-on-line.com] [www.ic-on-line.net]
[www.alldatasheet.com.cn]
[www.gdcy.com]
[www.gdcy.net] |