IS31LT3380 MR16 Lighting Evaluation Board Guide Quick Start Description The IS31LT3380 is a continuous mode inductive step-down converter, designed for driving a single LED or multiple series connected LEDs efficiently from a voltage source higher than the LED voltage. The chip operates from an input voltage between 8.5V and 40V and provides an output current up to 1.2A. The IS31LT3380 includes a high-side output current sensing circuit, which uses an external resistor to set the nominal average output current. The IS31LT3380 includes an integrated output switch which has a very low conducting impedance to ensure high system efficiency. The IS31LT3380 has switch dimming function; the chip detects external switch action to adjust output current, allowing for dimming functionality to be achieved without changing the original lighting system circuitry. The switch dimming is implemented in either two-level mode or three-level mode. The output current of every level and the total number of levels are customer selected by setting the corresponding input conditions of DIM1 and DIM2 pin. The output current is set at the initial value the first time that power is supplied to the chip. After the initial power up sequence, the chip adjusts the output current according to the external switch action. After the lowest current level, the current cycles back to the initial value if more switch action is detected. If the power is switched off for longer than 2 seconds, the device will return to it’s initial state, and the output current will be set to the initial value the next time that power is applied. Recommended Equipment Power supply LED panel (LED arrays) Multimeter Absolute Maximum Ratings ≤ 25VAC power supply Caution: Do not exceed the conditions listed above, otherwise the board will be damaged. Procedure The IS31LT3380 Evaluation Board is fully assembled and tested. Follow the steps listed below to verify board operation. Caution: Do not turn on the power supply until all connections are completed. Features Multi-mode switch dimming Up to 1.2A output current High efficiency (up to 98%) Wide input voltage range: 8.5V to 40V Internal 40V power switch Typical 5% output current accuracy Inherent LED open/short-circuit protection Thermal shutdown protection circuitry Applications MR16, MR11 LED spotlight LED street lighting PAR LED bulb 1) 2) 3) 4) Connect the two terminals of the power supply to the AC1 and AC2 pin. Connect the negative of the LED panel (LED arrays) to the LED- terminal. Connect the positive of the LED panel (LED arrays) to the LED+ terminal. Turn on the power supply and the LED panel (LED arrays) will be light. Ordering Information PART # TEMP RANGE IC PACKAGE IS31LT3380_GRLS3_EBMR16 -40 °C to 105°C SO-8 (5.0x6.0mm) For pricing, delivery, and ordering information, please contact ISSI at [email protected] or call +1-408-969-6600 Integrated Silicon Solution, Inc. – www.issi.com R1.0, 18/12/2012 1 IS31LT3380 MR16 Lighting Evaluation Board Guide close to the LX pin as possible with low resistance connections to LX. Detailed Description LED Current Control The nominal average output current in the LED(s) is determined by the value of the external current sense resistor (RS) connected between VIN and ISENSE and in is given by: IOUT nom = 0.1/RS The table below gives values of nominal average output current for several preferred values of current setting resistor (RS) in the application circuit: RS (Ω) 0.083 0.15 0.3 Nominal average output current (mA) 1200 667 333 RS need to be chosen as a 1% accuracy resistor with enough power tolerance and good temperature characteristic to ensure stable output current. Inductor selection Recommended inductor values are in the range 47μH to 220μH. Higher values of inductance are recommended at higher supply voltages and low output current in order to minimize errors due to switching delays, which result in increased ripple and lower efficiency. Higher values of inductance also result in a smaller change in output current over the supply voltage range. The inductor should be mounted as PCB layout consideration VIN/GND pin The GND of the power supply usually has some distance between it and the chip GND pin, causing parasitic resistance and inductance, resulting in ground voltage bounce when the MOSFET switches. To minimize ground bounce, the ground pin of the chip should be soldered directly to the ground plane. Connecting a 0.1uF capacitor between the VIN and GND pins as close to the chip as possible minimizes the effects of ground bounce. LX pin The LX pin of the chip is a fast switching node, so PCB traces should be kept as short as possible. Coil and decoupling capacitors It is particularly important to mount the coil and the input decoupling capacitor close to the chip to minimize parasitic resistance and inductance, which will degrade efficiency. It is also important to take account of any trace resistance in series with current sense resistor RS (shown as R1 on schematic diagram). DIM pin The DIM pin is a high impedance input, when left floating this pin is pulled up to 3.3V by internal circuitry. Avoid running any high voltage traces close to the DIM pins. Setting Dimming Current-Level Pin Name / Setting DESCRIPTION DIM 1 (pin 6) DIM 2 (pin 5) Functionality Dimming Levels Floating Floating No Dimming 100% Floating GND 3 (Three) - levels of dimming 100% -- 50% -- 20% GND Floating 3 (Three) - levels of dimming 100% -- 60% -- 30% GND GND 2 (Two) - levels of dimming 100% -- 30% The operation of the power switch and the configuration of the DIM1 and DIM2 pins control the dimming process as follows： 1. When DIM1 and DIM2 pins are both floating, there is no switch dimming, and the output current is 100% of the programmed value when the power is on. 2. When DIM1 is floating and DIM2 is GND, the output current is： a) 100% at power on. b) The first switch dimming action causes the current to change to 50%. Integrated Silicon Solution, Inc. – www.issi.com R1.0, 18/12/2012 3. 4. c) A second switch dimming action causes the current to return to 20%. d) A fourth switch dimming action has the same effect as the first switch dimming action. e) Subsequent switch dimming actions causes the cycle to continue. When DIM1 is GND and DIM2 is floating, the dimming sequence is as described in (2) above, except that the current sequence is 100%-60%-30%. When both DIM1 and DIM2 are connected to GND, the dimming sequence is as described in (2) above, 2 IS31LT3380 MR16 Lighting Evaluation Board Guide except that the current sequence is 100%-30%. If the switch is operated normally, that is, switched ON once after being in the OFF position for a long time, or if both the DIM1 and DIM2 pins are floating, then the output current always starts up at the initial value of 100%. R1 D5 D1 D1 Switch D2 Halogen Electronic Transformer AC110~220 1 ISENSE VIN C1 D3 C2 LX IS31LT3380 DIM1 D4 C3 2 DIM2 GND 7 L1 8 6 5 R3 R2 Figure 1 IS31LT3380 Evaluation Board Schematic Note: ISSI Evaluation Board does not include an Electronic Transformer or LED array Bill of Materials No. 1 2 3 4 5 6 7 8 Name SMD Diode AL Capacitor SMD Capacitor SMD Capacitor SMD Resistor SMD Resistor SMD Resistor SMD Inductor Description 2A,40V 330uF,25V 0.1uF,50V 1uF,250V 0.15Ω,(1206),1% 0Ω,(0805) 0Ω,(0805) 47µH,Isat＞1000mA Ref Des. L1 Qty. 5 1 1 2 1 1 1 1 9 IC IS31LT3380 U1 1 Integrated Silicon Solution, Inc. – www.issi.com R1.0, 18/12/2012 D1-D5 C1 C2 C3 R1 (RS) R2 R3 Mfr P/N 3 IS31LT3380 MR16 Lighting Evaluation Board Guide PCB Layout Figure 2 PCB Layout- Top Layer Figure 3 PCB Layout-Bottom Layer Copyright © 2011 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. – www.issi.com R1.0, 18/12/2012 4