IS31LT3938 Bulb Lighting DEMO Board Guide

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1 Description IS31LT3938 LED driver IC is a peak current detection buck converter which operates in constant off time mode. It operates over a very wide input voltage supply range of 10VDC to 450VDC or 110VAC/220VAC. IS31LT3938 incorporates the special feature of power sequencing by detecting OFF-ON cycles of the main power switch. When the switch is cycled within a 4 second period (typical) the device automatically switches the power sequencing level to the next step. As a result, power sequencing can be achieved without replacing any wiring in the original system. There are multiple modes of power sequencing that the user may configure, 2 steps or 3 steps, as well as different levels of power sequencing via the external pins DIM1 and DIM2. Features User configurable power sequencing levels 3% output current accuracy Over current, voltage and temperature protection High efficiency (typical up to 95%) Wide input voltage range: 10VDC-450VDC or 85Vac-265Vac Linear and PWM dimming Very few external components Applications DC/DC or AC/DC LED driver applications Signal and decorative LED lighting backlighting LED driver Order information Part Number IS31LT3938-GRLS2-EBBULB Package Type SOP-8 Quick Start Recommended Equipment 85~265VAC/50~60Hz power supply LED array(7 LEDs in series) Recommended Input and Output Ratings Input: 85~265VAC Output: 7LEDs in series(23v)/330ma Absolute Maximum Ratings 265VAC power supply 26V Vout (Total Vf) Caution: Do not exceed the conditions listed above, otherwise the board will be damaged or the output will be limited. Procedure The IS31LT3938 DEMO 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) Connect the positive terminal of the LEDs to the LED+ pin of the DEMO and the negative terminal of the LEDs to the LEDpin of the DEMO. 2) Connect the input pins (L and N) of the DEMO via the main power switch to AC power supply. 3) Turn on the power supply. Detailed description Switchable Power Levels The action of the main power switch can be divided into two types. The first is normal switch operation wherein the switch is toggled from ON to OFF, remaining OFF for longer than 4 seconds (typical). The other is power sequencing action wherein the switch is toggled from ON to OFF and back ON within 4 seconds (typical). When the device experiences normal switch Integrated Silicon Solution, Inc. 1

2 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 by connecting the DIM1 and DIM2 pins as indicated in the table below: DIM1 DIM2 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 will always power up at 100% output current. The operation of the power switch and the configuration of the DIM1 and DIM2 pins control the power sequencing process as follows: 1. When DIM1 and DIM2 pins are both floating, there is no power sequencing, and the output current is 100% of the programmed value when the power is on. 2. When DIM1 is floating and DIM2 is GND, the output current is: a) 100% at power on. b) The first power sequencing action causes the current to change to 30%. c) A second power sequencing action causes the current to return to 100%. d) A fourth power sequencing action has the same effect as the first power sequencing action. e) Subsequent power sequencing actions causes the cycle to continue. 3. When DIM1 is GND and DIM2 is floating, the power sequencing is as described in (2) above, except that the current sequencing is 100%-50%-100%. 4. When both DIM1 and DIM2 are connected to GND, the power sequencing is as described in (2) above, except that the current sequencing is 100%-50%-20%-100%. If the switch is operated normally, that is, switched on once after being in the OFF position for a long time, or if both the DIM1 and DIM2 pins are floating, then the output current always starts up at the initial value of 100%. Note: Because the main power switch is used to initiate the power sequencing function, the device must have a large enough external capacitor on VIN to maintain device operation for 4 seconds. Please refer to the Applications Examples for specific values. Integrated Silicon Solution, Inc. 2

3 Bill of Materials No. Name Description Ref Des. Qty. Cost(RMB) 1 Fuse 1A,250V,3*10 F AL Cap 10uF±10%,400V C2,C SMD Cap 10uF±20%,25V,0805 C Inductor 3mH±10%,8*10mm,Isat 200mA L Inductor 4.7uH±10%,5.6*5.6mm,Isat 1A L EE Inductor 1.8mH±5%,Isat 700mA,EE13 L Rectifying Bridge 0.5A,600V, SOIC-4 BR Zener Diode 12V,0.25W,LL-34 D FR Diode 1A,600V,ES1J,SMA D1,D Resistor NC R Resistor 75KΩ±5%,1W R3-1,R Resistor 470KΩ±1%,0805 R Resistor 1.5Ω±1%,1206 R Resistor 0.91Ω±1%,1206 R NMOS 4N60,4A/600V,TO-251 Q PCB 47mm x 20mm IC IS31LT3938,SOP-8 U1 1 Total Cost(Exclude IC) Note: 1. If the input voltage is single voltage(85~130vac or 178~265VAC), L4 and D1 can be removed (short the L3 and eliminate D3) and the efficiency will be higher. 2. If adding the opto-couple as the open output voltage limitation, C6 can use 35V tolerance rating to saving size and decreasing the output current ripple. Figure 1. Picture of DEMO Board NOTE: Physical dimensions are (L x W x H): 47mm x 20mm x 19mm Integrated Silicon Solution, Inc. 3

4 Figure 2. Schematic of DEMO Board Figure 3. PCB Layout- Top Layer Figure 4. PCB Layout- Bottom Layer Figure 4 Component Placement Guide -Top Layer Figure 5 Component Placement Guide -Bottom Layer Test result Line regulation Input Input Output Output Output PF voltage(vac) power(w) current(ma) voltage(v) power(w) Efficiency(%) Integrated Silicon Solution, Inc. 4

5 EMI test Figure 6. L line Integrated Silicon Solution, Inc. 5

6 Figure 7. N line 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. 6