TECHNICAL DATA White LED Step-Up Converter IL1937 Description The IL1937 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 battery. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The IL1937 operates at 1. 2MHz, allowing the use of tiny external components. The output capacitor can be as small as 0.22uF, saving space and cost versus alternative solutions. A low 95mV feedback voltage minimizes power loss in the current setting resistor for better efficiency. The device can used in mobile phones, PDAs, Handheld Computers, calculators, digital cameras, MP3-players, GPS-receivers Features Internally determined LED current High Efficiency: 84% Typical Drives Up to 4 LEDs from a 3.2V Supply Drives Up to 6 LEDs from a 5V Supply 36V rugged bipolar switch Fast 1.2MHz switching frequency Uses tiny 1mm Tall Inductors Requires only 0.22uF output capacitor Applications Cellular Phones PDAs, Handheld Computers Digital Cameras MP3 Players GPS Receivers Pin Description 1 2011, April, Ver. 01 IL1937 Block diagram VIN FB SW 03 06 01 A1 A3 Reference voltage source R1 + R3 A5 RS -flip-flops VT1 + R2 A2 C1 A4 + R4 _ Sawtooth voltage generator 02,05 GND SHDN 04 Oscilator A1 – error amplifier; A2 – addrer; A3 – PWM – comprator; A4 – comparator; A5 –driver; C1 – capacitor; R1 – R4 – resistor; VT1 – transistor Te device contain, switch on/off circuit; output current overrising protection unit, driver-buffer, output switch. 2 2011, April, Ver. 01 IL1937 Absolute maximum ratings Symbol VIN VSW VFB V SHDN TJ Тstg Absolute maximum ratings Min. Max. 10 36 10 10 150 -60 150 Parameter Input voltage SW pin Voltage FB pin Voltage SHDN pin Voltage Junction Temperature Storage Temperature Unit V V V V o C o C * Stresses beyond 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-rated conditions for extended periods may affect device reliability. Recommended operating mode Symbol VIN TJ Recommended operating mode Min. Max. 2,5 10 125 Parameter Input voltage Junction Temperature Unit V C o Electric Parameters Parameter, unit Minimum input voltage, V Maximum input voltage, V Symbol VIN MIN VIN MAX VFB Feedback Voltage, mV FB pad Bias Current, nA IFB Value Min. Max. 2,5 2,5 10 10 86 104 76 114 Testing mode Ambient temperature, C V SHDN = 3,0 V 10 10 100 150 VIN = 3,0 V, V SHDN = 3,0 V, ISW = 100 mA Duty Cycle 66 % VIN = 3,0 V, V SHDN = 3,0 V - 2,5 3,75 1,0 2,0 1,6 1,8 VIN = 3,0 V, V SHDN = 3,0 V VIN = 3,0 V, V SHDN = 0 V VIN = 3,0 V, V SHDN = 3,0 V - VIN = 3,0 V, V SHDN = 3,0 V VIN = 3,0 V, V SHDN =3,0V, VSW = 5,0 V 25 10 -40 … +125 Supply Current, mA IQ - ua Switching Frequency, Mhz Maximum Duty Cycle, % Switch Leakage Current, uA fS 0,8 0,6 DCMAX 85 80 - ILSW 5,0 7,5 3 2011, April, Ver. 01 IL1937 Symbol Parameter, unit VIH SHDN Voltage High, V VIL SHDN Voltage Low , V Value Min. Max. 1,5 1,5 0,4 0,4 Testing mode Ambient temperature, C VIN = 3,0 V Note 1 VIN = 3,0 V Note 1 25 10 -40 … +125 Notes 1 During VIH & VIL measurements threth hold voltage is tested, which has to be within range from 0,4 to 1,5 V 2 Symbol descriptions : - V SHDN - Shutdown pad voltage - VFB – Feedback Voltage pad voltage - VSW – Switch pad voltage - ISW – Switch pad current VI, V IC is switched on IC is switched off VIL=0,4V VIH=1,5V VSHDN, V Typical Electric Parameters Symbol ICL VCESAT ISHDN Parameter, unit Testing mode Output transistor current limit VIN = 3,0 V, V SHDN = 3,0 V Output transistor saturation VIN = 3,0 V, V SHDN = voltage 3,0 V, ISW = 250 мА VIN = 3,0 V, V SHDN = SHDN pad (pin) bias current 3,0 V 4 Typ.value Unit 320 mA 350 mV 65 uA 2011, April, Ver. 01 IL1937 OPERATION DESCRIPTION The IL1937 consist of following units: voltage switch on/off circuit, sawtooth generator, rectangular pulse generator PWM –comparator RS-latch, error amplifier, output buffer, output switch, currentlimit circuit for output switch. The IL1937 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. At the start of each oscillator cycle, signal from oscillator applied to S-pin of the RS-latch, the latch output high level voltage is set. This voltage through buffer turns on the power switch (transistor VT1). A voltage proportional to the switch current is added to a stabilizing sawtooth voltage and the resulting sum is applied to the positive terminal of the PWM comparator A3. When this voltage exceeds the level at the negative input of A3, the SR latch is reset turning off the power switch VT1. The level at the negative input of A3 is set by the error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 95mV. In this way, the error amplifier A1 contols the peak current level to keep the output in regulation. If the error amplifier’s output increases, more current is delivered to the output; if it decreases, less current is delivered. Typical application diagramm (3 white LED driver supplied by Li-ion battery) L1 22uHn VIN 3 to 5 V VD1 C1 1мк C2 0,22uF VD2 VIN SW VD3 15 mA IL1937 OFF ON VD4 FB SHDN GND 5 R1 6,34Ohm 2011, April, Ver. 01 IL1937 PACKAGE DIMENSION SOT-23-6 Symbol A A1 A2 b c D E E1 e e1 L L1 θ Dimensions In Millimeters Min 1.050 0.000 1.050 0.300 0.100 2.820 1.500 2.650 Dimensions In Inches Max 1.250 0.100 1.150 0.500 0.200 3.020 1.700 2.950 Min 0.041 0.000 0.041 0.012 0.004 0.111 0.059 0.104 2.000 0.071 0.600 8° 0.012 0° 0.950TYP 1.800 0.037TYP 0.600REF 0.300 0° Max 0.049 0.004 0.045 0.020 0.008 0.119 0.067 0.116 0.079 0.024REF 6 0.024 8° 2011, April, Ver. 01