ISSI IS31LT3918 User manual

IS31LT3918 T8 Lighting Evaluation Board Guide
Integrated Silicon Solution, Inc. – www.issi.com 1
R1.0, 18/12/2012
Description
The IS31LT3918 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 6VDC to 450VDC or 110VAC/220VAC.
The IS31LT3918 incorporates the special feature of
switch dimming by detecting OFF-ON cycles of the main
power switch. When the switch is cycled within a 2
second period (typical) the device automatically switches
the dimming level to the next step. As a result, dimming
can be achieved without replacing any wiring in the
original system. There are multiple modes of switch
dimming that the user may configure, 2 steps or 3 steps,
as well as different levels of dimming via the external
pins DIM1 and DIM2.
Features
User configurable switch dimming levels
3% output current accuracy
Over current, voltage and temperature protection
High efficiency (typical up to 95%)
Wide input voltage range: 6VDC~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
Quick Start
Recommended Equipment
85 ~ 265VAC 50~60Hz power supply
LED array (12 in series and 24 in parallel)
Main power switch
Absolute Maximum Ratings
≤265VAC power supply
≤42V Vout (Total Vf)
Caution: Do not exceed the conditions li
sted above, otherwise the board will be
damaged or the output will be limited
Procedure
The IS31LT3918 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.
Input
85 – 265VAC
LED
Array
IS31LT3918
Board
N
L
N
L
LED-
LED+
Switch
1) Connect the positive terminal of the LEDs to the
LED+ pin of the Evaluation Board and the negative
terminal of the LEDs to the LED- pin of the
Evaluation Board.
2) Connect the input pins (L and N) of the Evaluation
Board via the main power switch to AC power
supply.
3) Turn on the power supply.
Ordering Information
PART # TEMP
RANGE IC PACKAGE
IS31LT3918_GRLS2_EBT8 -40 °C to
85°C
SO-8
(5.0 x 6.0mm)
For pricing, delivery, and ordering information, please contact ISSI at [e-mail]
or call [phone]

IS31LT3918 T8 Lighting Evaluation Board Guide
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R1.0, 18/12/2012
Detailed Description
Switch Dimming
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 2 seconds (typical). The
other is “switch dimming 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.
Switch dimming output current levels are configured by
connecting the DIM1 and DIM2 pins as indicated in the
table below：
Setting Dimming Current-Level
Pin Name / Setting DESCRIPTION
DIM 1 DIM 2 Functionality Dimming Levels
Floating Floating No Dimming 100%
Floating GND 3 (Three) - levels of dimming 100% -- 30% -- 100%
GND Floating 3 (Three) - levels of dimming 100% -- 50% -- 100%
GND GND 2 (Two) - levels of dimming 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 dimming process
as follows：
1. When DIM1 and DIM2 pins are both floating, there
is no switch dimming, 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 switch dimming action causes the
current to change to 30%.
c) A second switch dimming action causes the
current to return to 100%.
d) A fourth switch dimming action has the same
effect as the first switch dimming action.
e) Subsequent switch dimming actions causes
the cycle to continue.
3. When DIM1 is GND and DIM2 is floating, the
dimming sequence is as described in (2) above,
except that the current sequence is
100%-50%-100%.
4. When both DIM1 and DIM2 are connected to GND,
the dimming sequence is as described in (2) above,
except that the current sequence 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 switch dimming function, the device must have a
large enough external capacitor on VIN to maintain
device operation for 2 seconds. Please refer to the
schematic for specific values.

IS31LT3918 T8 Lighting Evaluation Board Guide
Integrated Silicon Solution, Inc. – www.issi.com 3
R1.0, 18/12/2012
R1 R6
Figure 1 IS31LT3918 Evaluation Board Schematic
Note: ISSI Evaluation Board does not include a LED array
Figure 2. Picture of Evaluation Board
NOTE: Physical dimensions are (L x W x H): 25.1mm x 17mm x 12mm
PCB Layout
Figure 3. PCB Layout- Top Layer
Figure 4. PCB Layout- Bottom Layer

IS31LT3918 T8 Lighting Evaluation Board Guide
Integrated Silicon Solution, Inc. – www.issi.com 4
R1.0, 18/12/2012
Bill of Materials
No. Name Description Ref Des. Qty.
Mfr P/N
1 Fuse 1A/250V F1 1
2 AL Capacitor 22uF,250V C1,C6 2
3 X Capacitor 0.1 uF,275V C3,C4 2
4 Film Capacitor 10nF,630V C5 1
5 SMD Capacitor 1uF,50V,0805,X7R C7 1
6 SMD Capacitor 10uF,25V,0805,X7R C8,C9 2
7 SMD Capacitor NC C10 1
8 Inductor 3mH,10%,8*10,Isat≥200mA L1,L4 2
9 Inductor 0.65mH,Isat≥800mA L2,L5 2
10 Inductor NC L3 1
11 Diode 1A,1000V,1N4007,SMA D1,D4-D6,D8-D10 7
12 FR Diode 1A,600V,ESIJ,SMA D2 1
13 FR Diode NC D3 1
14 Zener Diode 12V,5% D7 1
15 Schottky Diode 1A,60V,SS16,SMA D12 1
16 Resistor 20KΩ,1206,5% R0 1
17 Resistor 270KΩ,1206,5% R1,R6 2
18 Resistor 4.7KΩ,0805,5% R3,R5 2
19 Resistor 150Ω,0805,5% R4 1
20 Resistor 3KΩ,0805,1% R7 2
21 Resistor 10Ω,0805,5% R8 1
22 Resistor 0Ω,0805 R9,R10 2
23 Resistor 0.68Ω,0805,1% R11 1
24 Resistor 0.75Ω,0805,1% R12 1
25 Resistor 330KΩ,0805,1% R13 1
26 NMOS 4N60,4A/600V,TO-220 T1 1
27 NMOS AP2306,5A/30V,SOT-23 T2 1
28 IC IS31LT3918,SOP-8 U1 1

IS31LT3918 T8 Lighting Evaluation Board Guide
Integrated Silicon Solution, Inc. – www.issi.com 5
R1.0, 18/12/2012
Line Regulation Rate and Efficiency
Input Voltage Input Power PF Output Voltage Output Current Efficiency
AC：90V 17.63W 0.853 37.35V 0.420A 88.98%
AC：110V 17.55W 0.887 37.35V 0.421A 89.60%
AC：130V 17.65W 0.876 37.30V 0.424A 89.60%
AC：180V 18.09W 0.830 37.20V 0.434A 89.25%
AC：220V 18.57W 0.810 37.20V 0.440A 88.14%
AC：240V 18.82W 0.802 37.20V 0.442A 87.37%

IS31LT3918 T8 Lighting Evaluation Board Guide
Integrated Silicon Solution, Inc. – www.issi.com 6
R1.0, 18/12/2012
EMI Test Report
Figure 5. L line

IS31LT3918 T8 Lighting Evaluation Board Guide
Integrated Silicon Solution, Inc. – www.issi.com 7
R1.0, 18/12/2012
EMI Test Report
Figure 6. N line
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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.
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