IS31LT3938 DC-DC DEMO Board Guide Description IS31LT3938 LED driver IC is a peak current detection buck converter which operates in constant off time Output: 12LEDs in series/2A Note: The input voltage must be 3V higher than the output voltage(total Vf). Absolute Maximum Ratings mode. It operates over a very wide input voltage supply range of 6VDC to 450VDC or 110VAC/220VAC. ≤ 60VDC IS31LT3938 incorporates the special feature of power ≤ 42V Vout (Total Vf) sequencing by detecting OFF-ON cycles of the main Caution: Do not exceed the conditions listed above, otherwise power switch. When the switch is cycled within a 2 the board will be damaged or the output will be changed. second period (typical) the device automatically Procedure switches the power sequencing level to the next step. As a result, power sequencing can be achieved without The IS31LT3938 DEMO Board is fully assembled and replacing any wiring in the original system. There are tested. Follow the steps listed below to verify board multiple modes of power sequencing that the user may operation. configure, 2 steps or 3 steps, as well as different levels Caution: Do not turn on the power supply until all of power sequencing via the external pins DIM1 and connections are completed. DIM2. 1) to the DC+ of the board and the negative terminal Features User configurable power sequencing levels 3% output current accuracy Over current, voltage and temperature protection High efficiency (typical up to 95%) of power supply to the DC- of the board. 2) Wide input voltage range: 6VDC~450VDC or Linear and PWM dimming Very few external components Connect the positive of the LED panel (LED arrays) to the LED+ terminal. 4) Connect the negative of the LED panel (LED arrays) to the LED- terminal. 3) 85Vac~ 265Vac Connect the positive terminal of the power supply Turn on the power supply and the LED panel (LED arrays) will be light. Detailed description Applications DC/DC or AC/DC LED driver applications Signal and decorative LED lighting backlighting LED driver Power sequencing Order information The action of the main power switch can be divided into Part Number Package Type two types. The first is “normal switch operation” IS31LT3938-GRLS2-EBDCDC SOP-8 wherein the switch is toggled from ON to OFF, remaining OFF for longer than 2 seconds (typical). The Quick Start Recommended Equipment 60VDC power supply LED array(1W LED, 12 in series,6 in parallel) Main power switch Recommended Input and Output Ratings Input: 48VDC Integrated Silicon Solution, Inc. – www.issi.com R1.0, 9/29/2012 other is “power sequencing action” wherein the switch is toggled from ON to OFF and back ON within 2 seconds (typical). When the device experiences normal switch operation, it merely powers on in the first state when the power switch is toggled to ON, and the device turns off when the main power switch is changed to OFF. Power sequencing output current levels are configured 1 IS31LT3938 DC-DC DEMO Board Guide by connecting the DIM1 and DIM2 pins as indicated in the table below： DIM1(Pin1) DIM2(Pin2) Power sequencing levels Floating Floating No Power sequencing Floating GND 2levels：100%-30%-100% GND Floating 2levels：100%-50%-100% GND GND 3levels:100%-50%-20%-100% When operating the power switch normally the device 3. When DIM1 is GND and DIM2 is floating, the power will always power up at 100% output current. sequencing is as described in (2) above, except The operation of the power switch and the configuration that the current sequence is 100%-50%-100%. of the DIM1 and DIM2 pins control the power 2. When both DIM1 and DIM2 are connected to GND, the power sequencing is as described in (2) above, sequencing process as follows： 1. 4. When DIM1 and DIM2 pins are both floating, there except that the is no power sequencing, and the output current is 100%-50%-20%-100%. current sequence is 100% of the programmed value when the power is If the switch is operated normally, that is, switched on on. once after being in the OFF position for a long time, or if When DIM1 is floating and DIM2 is GND, the both the DIM1 and DIM2 pins are floating, then the output current is： output current always starts up at the initial value of a) 100% at power on. 100%. b) The first power sequencing action causes the Note: Because the main power switch is used to initiate current to change to 30%. the power sequencing function, the device must have a c) A second power sequencing action causes the current to return to 100%. large enough external capacitor on VIN to maintain device operation for 2 seconds. Please refer to the d) A fourth power sequencing action has the Applications Examples for specific values. same effect as the first power sequencing action. e) Subsequent power sequencing actions causes the cycle to continue. Figure 1. Schematic of DEMO Board Integrated Silicon Solution, Inc. – www.issi.com R1.0, 9/29/2012 2 IS31LT3938 DC-DC DEMO Board Guide Bill of Material No. 1 2 3 4 5 6 7 8 9 10 11 12 Name AL Capacitor SMD Capacitor SMD Capacitor Resistor Resistor Resistor Resistor Schottky Diode Inductor NMOS IC PCB Description 22uF±10%,100V 10uF±20%,25V,0805 NC 51KΩ±1%,0805 NC 0.3Ω±1%,1206 24KΩ±5%,1206 2A,60V,SS26,SMA 100uH,Isat≥3A 13N06L,11A,60V,TO-252 IS31LT3938,SOP-8 50mm*25mm Total cost(exclude IC) Ref Des. C1,C2 C3 C4 R1 R2,R3 R4,R5 R6 D1,D2 L1 Q1 U1 Qty. 2 1 1 1 2 3 1 2 1 1 1 1 Cost(RMB) 0.4 0.1 0 0.006 0 0.024 0.008 0.16 1.5 0.7 0.4 3.298 Figure 2. Picture of DEMO Board PCB Layout NOTE: Physical dimensions are (L x W x H): 50mm x 25mm x 14mm Figure 3. PCB Layout- Top Layer Figure 4 Component Placement Guide -Top Layer Integrated Silicon Solution, Inc. – www.issi.com R1.0, 9/29/2012 Figure 4. PCB Layout- Bottom Layer Figure 5 Component Placement Guide -Bottom Layer 3 IS31LT3938 DC-DC DEMO Board Guide Test result Line regulation Input Input Input Output Output Output voltage(VDC) current(A) power(W) voltage(V) current(A) power(W) 42 2.00 84.00 39.2 2.078 44 1.91 84.04 39.3 2.077 46 1.83 84.18 39.3 2.077 48 1.75 84.00 39.4 2.071 50 1.69 84.50 39.2 2.073 52 1.62 84.24 39.1 2.071 54 1.56 84.24 39.2 2.073 81.46 81.63 81.63 81.60 81.26 80.98 81.26 Efficiency(%) 96.97 97.13 96.97 97.14 96.17 96.13 96.46 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. – www.issi.com R1.0, 9/29/2012 4