IS31LT3380-GRLS3-TR

IS31LT3380 40V/1.2A LED DRIVER WITH SWITCH DIMMING September 2011 GENERAL DESCRIPTION FEATURES 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.   Multi-modes 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 Simple low parts count Typical 5% output current accuracy Up to 1MHz switching frequency Inherent LED open-circuit/short-circuit protection Thermal shutdown protection circuitry SOP-8 package APPLICATIONS     MR16, MR11 LED spotlight LED street lighting PAR LED bulb Other LED lighting 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 at the next time that power is applied. Lumissil Microsystems – www.lumissil.com Rev. A, 09/01/2011 1 IS31LT3380 TYPICAL APPLICATION CIRCUIT Figure 1 Typical Application Circuit Note: The capacitor, C2, can’t be removed. And it should be placed as close as possible to the VIN and GND pins, otherwise the operation might be abnormal. Lumissil Microsystems – www.lumissil.com Rev. A, 09/01/2011 2 IS31LT3380 PIN CONFIGURATION Package Pin Configuration SOP-8 PIN DESCRIPTION No. Pin Description 1 VIN Input voltage (8.5V to 40V). Decouple to ground with 0.1μF X7R ceramic capacitor close to device. While using the switch dimming function, connect a 220uF or higher capacitor close the device. 2 ISENSE Connect resistor RS from this pin to VIN to define nominal average output current IOUTnom =0.1/RS 3, 4 NC Not connect. Float required 5 DIM2 6 DIM1 7 GND Ground (0V) 8 LX Drain of power switch Set the current-levels number of and current ratio of each level of switch dimming function as below: DIM1=“floating” DIM2=“floating”, not dimming； DIM1=“floating” DIM2=“GND”, three-levels, 100%---50%---20%; DIM1=“GND” DIM2=“floating”, three-levels，100%---60%---30%; DIM1=“GND” DIM2=“GND”，two-levels，100%---30%。 Lumissil Microsystems – www.lumissil.com Rev. A, 09/01/2011 3 IS31LT3380 ORDERING INFORMATION Industrial Range: -40°C to +105°C Order Part No. Package QTY/Reel IS31LT3380-GRLS3-TR SOP-8, Lead-free 2500 Copyright  ©  2011  Lumissil  Microsystems.  All  rights  reserved.  Lumissil Microsystems reserves  the  right  to  make  changes  to  this  specification  and  its  products  at  any  time  without  notice.  Lumissil  Microsystems  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.  Lumissil Microsystems 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 Lumissil Microsystems 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 Lumissil Microsystems is adequately protected under the circumstances Lumissil Microsystems – www.lumissil.com Rev. A, 09/01/2011 4 IS31LT3380 ABSOLUTE MAXIMUM RATINGS (NOTE 1) Input voltage, VIN ISENSE voltage, VSENSE -0.3V ~ +50V VIN-5V ~ VIN+0.3V, VIN>5V LX output voltage, VLX DIM1, DIM2 pin input voltage, VDIM Switch output current, ILX Power dissipation, PD(MAX) (Note 2) Operating temperature, TA = TJ Storage temperature, TST Junction temperature, TJMAX Junction to ambient, θJA -0.3V ~ VIN+0.3V, VIN 200ns. REDUCING OUTPUT RIPPLE LX Switch 'OFF' time: Peak to peak ripple current in the LED can be reduced, if required, by shunting a capacitor C3 across the LED(s) as shown below: t OFF  VLED L  I  VD  I AVG ( RL  RS ) Note: tOFF_MIN > 200ns. Where: L is the coil inductance (H) RL is the coil resistance (Ω) IAVG is the required LED current (A) ∆I is the coil peak-peak ripple current (A) {Internally set to 0.3 × IAVG} VIN is the supply voltage (V) VLED is the total LED forward voltage (V) Lumissil Microsystems – www.lumissil.com Rev. A, 09/01/2011 A C3 value of 1μF will reduce nominal ripple current by a factor of approximately three. Proportionally 11 IS31LT3380 lower ripple can be achieved with higher capacitor values. Note that the capacitor will not affect operating frequency or efficiency, but it will increase start-up delay, by reducing the rate of rise of LED voltage. THERMAL CONSIDERATIONS When operating the chip at high ambient temperatures, or when driving maximum load current, care must be taken to avoid exceeding the package power dissipation limits. Note that the chip power dissipation will be a maximum at the minimum supply voltage. It will also increase if the efficiency of the circuit is low. This may result from the use of unsuitable coils, or excessive parasitic output capacitance on the switch output. LAYOUT CONSIDERATIONS 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. Lumissil Microsystems – www.lumissil.com Rev. A, 09/01/2011 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 Capacitor 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. DIM Pin The DIM pin is a high impedance input, when it is left floating; this pin is pull up to 3.3V by internal circuit. Avoid running any high voltage traces close to the DIM pins. 12 IS31LT3380 PACKAGE INFORMATION SOP-8 Lumissil Microsystems – www.lumissil.com Rev. A, 09/01/2011 13