L1937 UTC | Alldatasheet
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UTC L1937 LINEAR INTEGRATED CIRCUIT UTC UNISONIC TECHNOLOGI ES CO., LTD. 1 QW-R103-021,A WHITE LED STEP-UP CONVERTER
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 DŽF , saving space and cost versus alternative solutions. A low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency.
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 0.22DŽF Output Capacitor
APPLICATIONS
- Marking code: LTCG * Cellular Phones * PDAs, Handheld Computers * Digital Cameras * MP3 Players * GPS Receivers SOT-25 SOT-363 *Pb-free plating product number: L1937L PIN FUNCTION PIN NO. (SOT-25) PIN NO. (SOT-363). PIN NAME SYMBOL FUNCTION 1 Switch SW Connect inductor/diode here. Minimize trace area at this pin to reduce EMI. 2 Ground GND Connect directly to local ground plane.
3 Feedback FB
Reference voltage is 95mV. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: R FB = 95mV/ILED
4 Shutdown
Connect to 1.5V or higher to enable device;0.4V or less to disable device. 5 6 Input Supply VIN Input Supply Pin. Must be locally bypassed.
5 Ground GND Connect to Pin 2 and to local ground plane
UTC L1937 LINEAR INTEGRATED CIRCUIT UTC UNISONIC TECHNOLOGI ES CO., LTD. 2 QW-R103-021,A BLOCK DIAGRAM VREF 1.25V 3 1 SHDN SHUTDOWN 95mV VIN FB( PIN 6 FOR SOT-363 PACKAGE ) + A1 - Rc Cc Ʋ RAMP GENERATOR 1.2MHz OSCILIATOR R S Q DRIVER SW GND ( PINS 2 AND 5 FOR SOT-363 PACKAGE ) 0.2Ƹ COMPARATOR ABSOLUTE MAXIMUM RATINGS PARAMETER SYMBOL RATINGS UNIT Input Voltage V IN 10 V SW Voltage V SW 36 V FB Voltage V FB 10 V SHDN Voltage V SHDN 10 V Operating Temperature Topr -40 ~ +85 Ċ Storage Temperature Tstg -65 ~ +150 Ċ Maximum Junction Temperature T j 125 Ċ Lead Temperature (Soldering, 10 sec) T Lead 300 Ċ ELECTRICAL CHARACTERISTICS (Ta=25Ċ, VIN=3V, VSHDN=3V, unless otherwise noted.) PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT Operating Voltage V IN 10 V Feedback Voltage V FB I SW=100mA,Duty Cycle=66% 86 95 104 mV FB Pin Bias Current I FB 10 45 100 nA Supply Current Icc SHDN=0V 1.9 0.1 2.5 1.0 mA µA Switching Frequency f osc 0.8 1.2 1.6 MHz Maximum Duty Cycle DC 85 90 % Switch Current Limit I SW 320 mA Switch VCESAT V CESAT(SW) ISW=250mA 350 mV Switch Leakage Current I SW(OFF) VSW=5V 0.01 5 µA SHDN Voltage High V IH 1.5 V SHDN Voltage Low V IL 0.4 V SHDN Pin Bias Current I SHDN 65 µA
UTC L1937 LINEAR INTEGRATED CIRCUIT UTC UNISONIC TECHNOLOGI ES CO., LTD. 3 QW-R103-021,A TYPICAL APPLICATIONS Li-Ion Powered Driver for Three White LEDs LED CURRENT (mA) 1510 Conversion Efficiency EFFICIENCY(%) VIN=3V VIN=3.6V VIN SW SHDN FB GND LED 1 LED 2 LED 3 6.34Ƹ 15mA 0.22DŽF 1DŽF VIN 3V ~ 5V OFF ON 22DŽF D1 VIN SW SHDN FB GND R1 COUT 1DŽF CIN 1DŽF VIN 3V ~ 5V L 22DŽH D 90k VDC DIMMING Li-Ion to Two White LEDs LED CURRENT (mA) 100 3020 Two LED Efficiency EFFICIENCY(%) VIN=3V VIN=3.6V
UTC L1937 LINEAR INTEGRATED CIRCUIT UTC UNISONIC TECHNOLOGI ES CO., LTD. 4 QW-R103-021,A LOAD CURRENT (mA) 1210 Five LED Efficiency EFFICIENCY(%) VIN=3V 862 VIN=3.6V LED CURRENT (mA) 1510 Three LED Efficiency EFFICIENCY(%) VIN=3V VIN=3.6V VIN SW UTC LT1937 SHDN FB GND R1 COUT 0.22DŽF CIN 1DŽF VIN 3V ~ 5V L 22DŽH D 90k VDC DIMMING Li-Ion to Three White LEDs VIN SW SHDN FB GND R1 COUT 0.22DŽF CIN 1DŽF VIN 3V ~ 5V L 22DŽH D 90k VDC DIMMING Li-Ion to Five White LEDs
UTC L1937 LINEAR INTEGRATED CIRCUIT UTC UNISONIC TECHNOLOGI ES CO., LTD. 5 QW-R103-021,A VIN SW SHDN FB GND R1 COUT 0.22DŽF CIN 1DŽF VIN 3V ~ 5V L 22DŽH D 90k VDC DIMMING Li-Ion to Four White LEDs LOAD CURRENT (mA) Four LED Efficiency EFFICIENCY(%) VIN=3V VIN=3.6V LOAD CURRENT (mA) Seven LED Efficiency EFFICIENCY(%) VIN SW SHDN FB GND R1 COUT 0.22DŽF CIN 1DŽF VIN L 22DŽH D 90k VDC DIMMING 5V to Seven White LEDs
UTC L1937 LINEAR INTEGRATED CIRCUIT UTC UNISONIC TECHNOLOGI ES CO., LTD. 6 QW-R103-021,A TYPICAL PERFORMANCE CHARACTERISTICS 2.2 VIN (V) 0.8 0.4 1.2 1.6 2.0 Quiescent Current IQ (mA) 25Ċ 100Ċ -50Ċ 1.8 1.4 1.0 0.6 0.2 400 TEMPERATURE (Ċ) -25-50 250 150 250 350 300 200 100 SHDN Pin Bias Current 100 SHDN=3.6V SHDN=3V SHDN=2.7V SHDN=10V 1.4 -25-50 250 0.4 0.8 1.2 1.0 0.6 0.2 50 100 Switching Frequency TEMPERATURE (Ċ) SWITCHING FREQUENCY (MHz) -25-50 250 50 100 Feedback Bias Current TEMPERATURE (Ċ) FEEDBACK CURRENT (nA) -50 0 50 100 Efficiency vs Temperature TEMPERATURE (Ċ) Efficiency(%) 350 200 6040 100 200 300 250 150 80 100 Current Limit vs Duty Cycle DUTY CYCLE (%) CURRENT LIMIT (mA) ILED=20mA ILED=15mA ILED=10mA VIN=3.6V
3 LEDs
SHDN PIN BIAS CURRENT (DŽA)
UTC L1937 LINEAR INTEGRATED CIRCUIT UTC UNISONIC TECHNOLOGI ES CO., LTD. 7 QW-R103-021,A 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.