IS31LT3171 10-TO-150mA CONSTANT-CURRENT LED DRIVER DESCRIPTION RECOMMENDED EQUIPMENT The IS31LT3171 is adjustable constant current linear devices with excellent temperature stability. A single resistor is all that is required to set the operating current from 10mA to 150mA. The devices can operate from an input voltage from 2.5V to 42V with minimal voltage headroom of 0.6V. Designed with a low dropout voltage; the device can drive LED strings close to the supply voltage. As a current sink, it is ideal for LED lighting applications or as power supply current limiters. FEATURES Low-side current sink - Current preset to 10mA - Adjustable from 10mA to 150mA with external resistor selection Wide input voltage: 2.5V to 42V Up to 1W power dissipation in a small SOT23-6 package RoHS compliant (Pb-free) package Operating temperature range from -40°C ~ +125°C 42V, 500mA DC variable power supply 3 HBLEDs connected as a serial string ABSOLUTE MAXIMUM RATINGS ≤ 42V input voltage Caution: Do not exceed the conditions listed above, otherwise the board will be damaged. PROCEDURE The IS31LT3171 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. 1) 2) QUICK START Connect the ground terminal of the power supply to the GND (TP3) and the positive terminal to the VCC (TP1). Connect the Anode of an external LED string to LED+ (TP4) and its Cathode to LED(TP5). The evaluation board supports eight current levels, selected by JP1, JP2, JP3, see table below. The test point REXT can be used to add an external resistor. The final resistance can be measured with an ohm meter across REXT and GND (TP6) pins. For jumpers (JP1~JP3) Closed=1 and Open=0. Figure 1: Photo of IS31LT3171 Evaluation Board 3) JP1 JP2 JP3 REXT (Ω) 0 0 0 - 0 0 1 100 0 1 0 15 0 1 1 13 1 0 0 8.2 1 0 1 7.6 1 1 0 5.3 1 1 1 5.0 The 0Ω resistor R4 must be NC. Otherwise, the EN pin may be damaged by high voltage. ORDERING INFORMATION Part No. Temperature Range Package IS31LT3171-STLS4-EB -40°C ~ +125°C (Industrial) SOT-23-6, Lead-free Table 1: Ordering Information For pricing, delivery, and ordering information, please contact ISSI’s analog marketing team at [email protected] or (408) 969-6600 Integrated Silicon Solution, Inc. – www.issi.com Rev. A, 07/07/2015 1 IS31LT3171 10-TO-150mA CONSTANT-CURRENT LED DRIVER EVALUATION BOARD OPERATION IS31LT3171 evaluation board drives one string of WLEDs. There are three resistors used for adjusting the output current. OUTPUT CURRENT SETTING IS31LT3171 provides an easy constant current sink solution for LED lighting applications. It uses an external resistor to adjust the LED current from 10mA to 150mA. The LED current can be determined by the Equation (1): I SET 10mA RINT REXT Where RINT (106Ω, Typ.) is the device internal resistor and REXT is the external resistor. Paralleling a low tolerance resistor REXT with the internal resistor RINT will improve the overall accuracy of the current sense resistance. The resulting output current will vary slightly lower due to the negative temperature coefficient (NTC) resulting from the self heating of the IS31LT3171. (1) REXT Integrated Silicon Solution, Inc. – www.issi.com Rev. A, 07/07/2015 2 IS31LT3171 10-TO-150mA CONSTANT-CURRENT LED DRIVER VCC LED+ 2 1 1 2 TP1 TP4 LEDU1 2 R4 3 5 1 2 TP5 OUT REXT OUT OUT REXT 6 JP1 JP2 JP3 EN R1 2 1 1 EN GND TP2 R2 R3 4 IS31LT3171 GND GND 2 1 1 2 TP3 TP6 Figure 2: IS31LT3171 Application Schematic BILL OF MATERIALS Name Symbol LED Driver U1 Resistor Description Qty Supplier Part No. LED Driver 1 ISSI IS31LT3171 R1 RES,8R2,1/10W,±1%,SMD 1 YAGEO RC0805FR-078R2L Resistor R2 RES,15R,1/10W,±1%,SMD 1 YAGEO RC0805FR-0715RL Resistor R3 RES,100R,1/10W,±1%,SMD 1 YAGEO RC0805JR-07100RL Resistor R4 Not installed Jumper JP1~JP3 Jumper 3 Test Terminal TP1~TP6 Test terminal 6 Bill of materials, refer to Figure 2 above. Integrated Silicon Solution, Inc. – www.issi.com Rev. A, 07/07/2015 3 IS31LT3171 10-TO-150mA CONSTANT-CURRENT LED DRIVER 0 0 1 2 1 2 1 2 1 2 1 2 1 1 1 1 2 2 2 1 2 0 0 Figure 3: Board Component Placement Guide - Top Layer Figure 4: Board PCB Layout - Top Layer Integrated Silicon Solution, Inc. – www.issi.com Rev. A, 07/07/2015 4 IS31LT3171 10-TO-150mA CONSTANT-CURRENT LED DRIVER 0 0 1 2 1 2 1 2 1 2 1 2 1 1 1 1 2 2 2 1 2 0 0 Figure 5: Board Component Placement Guide - Bottom Layer Figure 6: Board PCB Layout - Bottom Layer Copyright © 2015 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, 07/07/2015 5