IS31LT3350 3CH EVALUATION BOARD GUIDE DESCRIPTION RECOMMENDED EQUIPMENT The IS31LT3350 is a continuous mode inductive 60VDC power supply step-down converter, designed for driving a single LED 3 pcs of LED panel (1 WLED, 10 LEDs in series or multiple series connected LEDs efficiently from a on each panel) voltage source higher than the LED voltage. The chip Multi-meter operates from an input supply between 6V and 40V and provides an externally adjustable output current of up to 750mA. Depending upon supply voltage and RECOMMENDED INPUT AND OUTPUT RATINGS external components, this can provide up to 30 watts Input: 6~40VDC of output power. Output: 1-10 LEDs in series/333mA The IS31LT3350 includes an integrated output switch Note: The input voltage must be 2V higher than the output and a high-side output current sensing circuit, which voltage (total V). f uses an external resistor to set the nominal average output current. Output current can be adjusted linearly by applying an external control signal to the ADJ pin. ABSOLUTE MAXIMUM RATINGS The ADJ pin will accept either a DC voltage or a PWM Input voltage 40VDC waveform. This will provide either a continuous or a gated output current. Applying a voltage of 0.2V or Caution: Do not exceed the conditions listed above otherwise the board will be damaged. lower to the ADJ pin turns the output off and switches the chip into a low current standby state. The chip is assembled in SOT23-5, SOT89-5 and PROCEDURE SOP8 package. SOT23-5 is available for 350mA output current application SOT89-5 and SOP8 is The IS31LT3350 demo board is fully assembled and tested. Follow the steps listed below to verify board available for 700mA output current application. operation. IS31LT3350 3CH Evaluation board is used in RGB Caution: Do not turn on the power supply until all connections lamp or the general LED lamp. are completed. FEATURES Simple low parts count Internal 40V power switch 1) Connect the terminals of the power supply to the Wide input voltage range: 6V to 40V AC1 and AC2 pin (If the board dont have the Up to 750mA output current rectifier (D1~D4). Connect the positive terminal of High efficiency (up to 95% ) the power supply to the VCC of the board and the Typical 1200:1 dimming rate negative terminal of power supply to the GND of Typical 5% output current accuracy the board). Single pin on/off and brightness control using DC 2) Connect the negative of the one of LED panel voltage or PWM (LED arrays) to the LED1- terminal. And connect Up to 1MHz switching frequency the positive of the same LED panel (LED arrays) to the LED1+ terminal. Inherent open-circuit LED protection 3) Connect the other two LED panels to LED2 and Thermal shutdown protection circuitry LED3 as above. 4) Turn on the power supply and the LED panels QUICK START (LED arrays) will be light. Figure 1: Photo of IS31LT3350 Evaluation Board Lumissil Microsystems www.lumissil.com 1 Rev. A, 08/26/2011 IS31LT3350 3CH EVALUATION BOARD GUIDE ORDERING INFORMATION Part No. Temperature Range Package IS31LT3350-V1SDLS2-EB3CH -40C to +85C (Industrial) SOT23-5 (5mm 6mm) Table 1: Ordering Information For pricing, delivery, and ordering information, please contacts Lumissils analog marketing team at analog Lumissil.com or (408) 969-6600. DETAILED DESCRIPTION lower efficiency. Higher values of inductance also result in a smaller change in output current over the LED Current Control supply voltage range. The inductor should be mounted as close to LX pin as possible with low resistance The nominal average output current in the LED(s) is connections to LX and VIN pins. determined by the value of the external current sense resistor (R ) connected between V and I and in S IN SENSE PCB Layout Consideration is given by: Decoupling Capacitors And Coil 0.1 (for R > 0.13 ) I S It is particularly important to mount the coil and the OUT NOM R S input decoupling capacitor close to the chip to minimize parasitic resistance and inductance, which The table below gives values of nominal average will degrade efficiency. The input decoupling capacitor output current for several preferred values of current (0.1 F fixed) must be placed as close to the VIN and setting resistor (Rs) in the typical application circuit. GND pins as possible. It is also important to take account of any trace resistance in series with current Nominal Average Output Current R ( ) S sense resistor R . S (mA) LX Pin 0.13 769 0.15 667 The LX pin of the chip is a fast switching node, so PCB traces should be kept as short as possible. To 0.27 370 minimize ground bounce, the ground pin of the chip 0.3 333 should be soldered directly to the ground plane. V is divided into two range to improve current SENSE ADJ Pin accuracy, please refer to bin information on page 3. The ADJ pin is a high impedance input, so when left The above values assume that the ADJ pin is floating floating, PCB traces to this pin should be as short as and at a nominal voltage of V =1.2V. REF possible to reduce noise pickup. ADJ pin can also be Note that R =0.13 is the minimum allowed value of S connected to a voltage between 1.2V~5V. In this case, sense resistor under these conditions to maintain the internal circuit will clamp the output current at the switch current below the specified maximum value. It is value which is set by ADJ=1.2V. possible to use different values of R if the ADJ pin is S High Voltage Traces driven from an external voltage. Avoid running any high voltage traces close to the ADJ Inductor Selection pin, to reduce the risk of leakage due to board Recommended inductor values are in the range 47 H contamination. Any such leakage may raise the ADJ to 220 H. Higher values of inductance are pin voltage and cause excessive output current. A recommended at higher supply voltages and low ground ring placed around the ADJ pin will minimize output current in order to minimize errors due to changes in output current under these conditions. switching delays, which result in increased ripple and Lumissil Microsystems www.lumissil.com 2 Rev. A, 08/26/2011