IS31LT3135 MAIN/SUB DUAL-CHANNEL LED DRIVER November 2011 GENERAL DESCRIPTION FEATURES IS31LT3135 is a main/sub dual-channel LED driver. When the main channel works，it is a constant current source driving the main LED and the current is set by an external resistor connected to the ISET pin. It needs only 0.1v dropout voltage for 200mA output current. When the sub-channel works, the chip will pull down the sub LED’s cathode to ground. Normally there is only one channel on, the main channel and the sub channel can switch between each other. Sweeping power supply from high voltage to low voltage, main channel switches to sub-channel while UV pin is below the undervoltage threshold 1.17V (IS31LT3135-V1 typical) or 1.23V (IS31LT3135-V2 typical). Sweeping power supply from low voltage to high voltage, the sub-channel switches to the main channel while UV pin is 80mV (typical) higher than the undervoltage threshold. Additionally, the main channel has short protection function, when the main LED is shorted，the chip will switch to sub-channel automatically. Power supply undervoltage detect Main channel short protection Over-temperature protection Input voltage range: 2.7V~5.5V Main and sub-channel current set by external resistor Main channel Vdp=0.1V Low quiescent current Assembled in SOP-8 package APPLICATIONS Miner lamp Other LED lighting TYPICAL APPLICATION CIRCUIT IS31LT3135 Figure 1 . 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 Rev.A, 11/08/2011 1 IS31LT3135 PIN CONFIGURATIONS Package Pin Configurations (Top View) SOP-8 PIN DESCRIPTION Name No. Description VCC 1 Power supply input UV 2 The pin detects under-voltage. Decouple to ground with 0.1uF capacitor close to device ISET 3 The pin sets the main LED current with external resistor GND 6 The pin connects to ground. MAIN 7 Connect to the cathode of main LED SUB 8 Connect to the cathode of sub LED NC 4，5 Not connected ORDERING INFORMATION Industrial Range: -40°C to +85°C Order Part No. Package QTY/Reel V UV IS31LT3135-V1GRLS2-TR SOP-8, Lead-free 2500 1.13V~1.21V IS31LT3135-V1GRLS2-TR SOP-8, Lead-free 2500 1.19V~1.26V Integrated Silicon Solution, Inc. — www.issi.com Rev.A, 11/08/2011 2 IS31LT3135 ABSOLUTE MAXIMUM RATINGS Supply voltage, VCC UV, Iset, Sub, Main Junction temperature, TJMAX Storage temperature range, Tstg ESD(human body mode) IMAIN ISUB TA( Ambient temperature) -0.3V ~ +6.5V -0.3V to 6.5V +150°C -65°C ~ +150°C 4kV 500mA 300mA -40°C ~ +85°C Note: 1. 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 condition beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (Test conditions: VCC=3.6V,Tamb=25℃ unless otherwise stated) Symbol Parameter Condition Min Typical VCC Input voltage 2.7 Icc Quiescent current Vcc=2.7V~5.5V,no load， 5.5V>Vuv>1.4V 250 Iratio Ratio of IMAIN to ISET VCC=4.2V，Rset=30K 8000 VISET Voltage of ISET pin Max Unit 5.5 V 320 μA 1.2 V ±5 % Current accuracy of main LED Vcc = 2.7V ~ 5.5V，Vmain=0.5V Vdp Main channel current source dropout voltage Rset=47K,Iout=204mA 0.2 V Rsub Sub-channel “ON” resistance Vcc=2.7V~5.5V 2.0 ohm Undervoltage threshold of UV pin Switch from main-LED to sub-LED when VUV sweeps from high voltage to low voltage Iaccuracy VUV VUVHYS Comparator hysteresis of UV pin(Upper threshold Undervoltage threshold) TSD Thermal protection Threshold RθJA Junction to ambient IS31LT3135-V1 Integrated Silicon Solution, Inc. — www.issi.com Rev.A, 11/08/2011 1.17 121 V IS31LT3135-V2 Switch from sub-LED to main-LED when VUV sweeps from low voltage to high voltage(Upper threshold); Switch from main-LED to sub-LED when VUV sweeps from high voltage to low voltage(Undervoltage threshold) SOP-8 1.13 1.19 1.23 1.26 80 mV 160 ℃ 80 °C/W 3 IS31LT3135 TYPICAL OPERATING CONDITION 1.2 Vset 1.19 1.18 1.17 1.16 1.15 10 20 30 40 50 60 70 temperature 80 90 100 Iset pin voltage change with temperature Figure 2 350 348 346 Imain(mA) 344 342 340 338 336 334 332 330 4 4.2 Figure 3 4.4 4.6 4.8 V DC (V) 5 5.2 5.4 Main LED current change with power supply Integrated Silicon Solution, Inc. — www.issi.com Rev.A, 11/08/2011 4 IS31LT3135 APPLICATION NOTES MAIN LED CURRENT SET Current of the main LED is set by resistor connected to Iset pin. Voltage of Iset pin is 1.2V. It is constant even if the environment temperature and power supply voltage changes.(Refer to figure2, figure3). The current of main channel is 8000 times to the current of Iset pin. It is obtained by: I main 8000 * Vset Rset Main LED current flows through the MAIN pin to ground. There is only 0.1V voltage dropout when the main channel current is 200mA (Note 1). SUB LED CURRENT SET Sub-LED current flows through SUB to ground. This current can be set by the resistor of SUB pin and is given by: I sub V VF2 Vd2 CC R SUB VCC is power supply voltage, VF2 is the sub-LED voltage. Vd2 is the diode voltage（Refer to Figure 1）， its value should be as small as possible. Typically，Li battery voltage maintains at 3.7V during discharge. Therefore, it is recommended to set the undervoltage threshold at 3.4V. Typically, R1 and R2 are set to 10K Ohm magnitude （e.g. 51K Ohm）, the current flows through R1 and R2 is large if the value of R1 and R2 are small, which will reduce system efficiency. We can specify the value of R2, and then calculate the value of R1 based on the ratio. MAIN LED SHORT PROTECTION When the main LED is short circuit, chip will switch to sub-channel automatically. OVER-TEMPERATURE PROTECTION When the chip temperature reaches 160℃, the chip turns off automatically. When temperature drops back to 140℃, the chip turns on again. PCB LAYOUT REFERENCE The switch should be placed at the low voltage point (Refer to Figure 1) to avoid an instant spark while switching. The traces between GND pin and Iset pin to real ground should be as short as possible and as wide as possible to improve the main LED current accuracy and undervoltage threshold accuracy. Adding a 0.1uF capacitor connected to UV pin can reduce the noise pick-up at this pin. UNDERVOLTAGE THRESHOLD SET UV pin has undervoltage detect function and the undervoltage threshold gets a 0.8V hysteresis to avoid error operation caused by power supply ripple. Sweeping power supply from high voltage to low voltage, the main channel switches to sub-channel while UV pin is below undervoltage threshold, 1.17V (IS31LT3135-V1 typical) or 1.23V (IS31LT3135-V2 typical). Sweeping power supply from low voltage to high voltage, the sub-channel switches to the main channel while UV pin is 80mV (typical) higher than the undervoltage threshold. Uuv is set by the ratio of resistor of R1 and R2 (Refer to Figure1). When R2 VCC =1.17V or 1.23V, chip switches R1 R 2 Note 1: When power supply voltage is larger than LED voltage, the extra voltage would be added on the Main pin, which will reduce the efficiency of the whole system. from the main channel to the sub-channel. Integrated Silicon Solution, Inc. — www.issi.com Rev.A, 11/08/2011 5 IS31LT3135 PACKAGE INFORMATION SOP-8 Integrated Silicon Solution, Inc. — www.issi.com Rev.A, 11/08/2011 6