IS31LT3135V1, IS31LT3135V2 Dual Ch. (Main/Sub) LED Driver Evaluation Board Guide Description Quick Start The IS31LT3135 is a dual‐channel LED driver that has two modes of operation; it can function as the main‐channel driver or as a sub‐channel source. When operating in main mode, the device functions as a constant current source that outputs an adjustable current, via an external resistor, through the main LED. The device is operable with a dropout voltage of 0.1V while driving a 200mA current. When operating as a sub‐channel driver, the IC grounds the LED’s cathode. The device normally operates with a single channel powered on, allowing for quick switching between the main and sub channel modes. A sweeping power supply that operates between high and low voltages, allows for simple switching between sub/main‐channel modes, even during conditions where the UV pin is below the 1.17V (typical) UV threshold IS31LT3135‐V1; or 1.23V (typical) UV threshold for IS31LT3135‐V2. The sweeping power supply allows sub‐channel to main channel switching during conditions where the UV pin is ≥80mV than the UV threshold. In addition, the main channel features short protection via switching to sub‐channel if any abnormal behaviors occur in the main‐channel LED circuitry. Features Power supply under‐voltage detection Main‐channel LED short protection Over‐temperature protection Input voltage range: 2.7V to 5.5V Main/sub‐channel adjustable output current (Set via user‐configurable external resistors) Main‐channel dropout VDP=0.1V Ultra‐low quiescent current SOP‐8 Package, small PCB footprint size Figure 1: Photo of IS31LT3135V1/V2 evaluation board Recommended Equipment 5VDC Power supply 1W LED Multi‐meter Recommended I/O Ratings Power supply voltage: 3.8VDC Output of IMAIN: 320mA per LED Output of ISUB: 20mA per LED Note: When the power supply voltage ≥ LED voltage rating, extra voltage is dissipated through the main‐channel, causing a drop in system efficiency and an increase in wasted energy. Absolute Maximum Ratings Input voltage ≤ 5VDC Caution: Do not exceed the input voltage conditions listed above to avoid risking permanent damage to the board. Ordering Information Part Number Temperature Range IS31LT3135‐V1GRLS2‐EB IS31LT3135‐V2GRLS2‐EB −40°C to +85°C (Industrial Grade) IC Package SOP‐8 (5mm x 4mm) Table 1: Ordering Information for IS31LT3135‐V1/V2 evaluation board. Customers with inquiries regarding pricing, delivery, part availability, and related information, can reach ISSI Analog marketing via either of the following methods: Email: [email protected] / Phone: +1 (408) 969‐6600 Integrated Silicon Solution, Inc. – http://www.issi.com V2, 4/23/2012 1 IS31LT3135V1, IS31LT3135V2 Dual Ch. (Main/Sub) LED Driver Evaluation Board Guide Procedure The IS31LT3135 evaluation board comes assembled and equipped with the purpose of allowing the user to easily demonstrate, or evaluate, functions of the IC driver. In order to verify device operation, please follow the listed directions carefully. Caution: When powering on the circuit; ensure that all connections are properly linked to complete the board circuitry. 1. 2. 3. 4. 5. Connect the negative terminal of the power supply to the GND pin. Connect the positive terminal of supply to the VCC pin. Connect the negative end of the LED panel (LED arrays) to the LED− terminal. Connect the positive end of the LED panel (LED arrays) to the LED+ terminal. After ensuring connections are sound and that the circuit is complete, turn on the power supply to drive current through the LED panel (LED arrays) and perform evaluation. Figure 2: IS31LT3135 evaluation board circuit schematic. Bill of Materials Name Capacitor Resistor Diode HBLED Driver IC Description Symbol Quantity 10uF±20%,16V, Surface‐mount, 0805 100nF±20%,50V, Surface‐mount, 0603 51K±1%, Surface‐mount, 0805 (V1) 47K±1%, Surface‐mount, 0805 (V2) 30K±1%, Surface‐mount, 0805 30K±1%, Surface‐mount, 0805 33±1%, Surface‐mount, 0805 Schottky type, SS16,1A, 60V, SMA IS31LT3135, SOP‐8 Package C1 C2 1 1 R1 1 R2 R3 R4 D1 U1 1 1 1 1 1 Table 2: IS31LT3135 Bill of Materials. Refer to Figure 2 for specific component locations Integrated Silicon Solution, Inc. – http://www.issi.com V2, 4/23/2012 2 IS31LT3135V1, IS31LT3135V2 Dual Ch. (Main/Sub) LED Driver Evaluation Board Guide Device Operation MainChannel LED Output Current The main‐channel LED current is adjusted by using a resistor connected to Iset pin. The voltage of Iset pin will remain at 1.2V, independent of external factors including transient temperature and source voltage fluctuations. The through the main‐channel LED is calculated by using the following equation: I MAIN 8000 VSET R SET The main‐channel current will continue through the LED to the GND pin. 0.1V dropout voltage occurs when the main‐channel current is ≤ 200mA. Sub‐channel LED current originates from the SUB terminal to ground, and likewise its corresponding LED current can be set via an external resistor. ISUB VCC VF2 VD2 R 4 R SUB VCC is the power supply voltage. VF2 is the sub‐LED voltage. VD2 denotes the diode voltage and its value should be minimized. UV Threshold Configuration The UV pin detects any voltage swings and compensates by utilizing 0.8v hysteresis. This form of error correction mechanism will ensure reliable device operation, even when the power supply experiences an unwanted ripple effect. Sweeping power supply from a high to low voltage, results in main channel switch to sub‐channel while UV pin is below the UV threshold of 1.17V (IS31LT3135‐V1 typical) or 1.23V (IS31LT3135‐V2 typical.) Sweeping power supply from a low to high voltage, will cause the sub‐channel mode to switch back to main‐channel operation, under conditions where UV pin is 80mV higher than the UV threshold. Uuv is set by the ratio of resistor R1 over resistor R2. R2 VCC 1.17 V (V1) or 1.23V(V2) ; an immediate switch from main to sub‐channel operation R1 R 2 When occurs. Lithium‐ion batteries typically maintain a voltage level of 3.7V during discharge, so the recommended UV threshold is 3.4V. Typically resistors R1 and R2 are set to 10K magnitude（i.e.51k）Small resistance values for R1 and R2 will translate to losses in heat or efficiency. To minimize these losses, it is recommended to derive precise values for the resistors so that the end device operates with the highest efficiency rate achievable. ShortCircuit Protection Mechanism When the main‐channel LED is shorted, IS31LT3135 will automatically switch to sub‐channel mode. PCB layout reference The switch should be placed in an area with low voltages, to avoid an instant spark while switching. The traces between GND pin and ISET pin to real ground should be as short and wide as possible, with the purpose of improving the main LED current accuracy and under voltage threshold accuracy. Adding a 0.1uF, capacitor may also help with this purpose. Integrated Silicon Solution, Inc. – http://www.issi.com V2, 4/23/2012 3 IS31LT3135V1, IS31LT3135V2 Dual Ch. (Main/Sub) LED Driver Evaluation Board Guide Figure 3: Component Placement: Top Layer Figure 4: PCB Layout‐ Top Layer Figure 5: Component Placement Guide ‐Bottom Layer Figure 6: Board PCB Layout‐Bottom Layer Copyright© 2012 Integrated Silicon Solution, Inc. All rights reserved. ISSI reserves the right to make changes to this specification and its products at any time without notice. ISSI assumes no liability arising out of the application or use of any information, products or services described herein. Customers are advised to obtain the latest version of this device specification before relying on any published information and before placing orders for products. Integrated Silicon Solution, Inc. does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless Integrated Silicon Solution, Inc. receives written assurance to its satisfaction, that: a) the risk of injury or damage has been minimized; b) the user assume all such risks; and c) potential liability of Integrated Silicon Solution, Inc. is adequately protected under the circumstances. Integrated Silicon Solution, Inc. – http://www.issi.com V2, 4/23/2012 4