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PDF IS31LT3918 Data sheet ( Hoja de datos )
| Número de pieza | IS31LT3918 | |
| Descripción | HIGH VOLTAGE LED LIGHTING DRIVER | |
| Fabricantes | ISSI | |
| Logotipo |  |
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IS31LT3918
HIGH VOLTAGE LED LIGHTING DRIVER WITH SWITCH DIMMING
OCTOBER 2011
GENERAL DESCRIPTION
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.
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.
IS31LT3918 can also realize LED dimming using an
external PWM signal. It can accept a PWM signal from
0% to 100% duty cycle. The LED current may also be
adjusted linearly by applying an analog input voltage in
the range of 0.5V to 2.5V.
IS31LT3918 adopts a peak current mode control
architecture, which eliminates the need for any
additional loop compensation while maintaining a good
degree of constant output current regulation.
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 constant current LED driver
Signal and decorative lighting
Backlight LED driver
TYPICAL APPLICATION CIRCUIT
Switch K
D1
85Vac- 265Vac
D3
Fuse
D2
C1
D4
R2
C6
C4
R1
C2
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R5
DZ
D6
D5 C3
L1
Q2
VIN Gate
DIM1
CS
IS3I1SL3T9319818
DIM2
ADJ
GND
TOFF
R6
R3
Q1
R4
LED+
LED-
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, 09/01/2011
1
datasheet pdf - http://www.DataSheet4U.net/
1 page  
IS31LT3918
Oscillator
IS31LT3918’s TOFF pin controls the off time of the
internal oscillator. Oscillator off time is determined by
the following equation:
Toff (s) 40 1012 REXT
REXT：resistor connected between TOFF and GND
Switch Dimming
IS31LT3918 detects the external switch action of the
main power switch, and can automatically adjust the
level of the output current based on the action of the
main power switch.
The action of the external power switch can be divided
into two types. The first is “normal switch operation” in
which the switch is toggled from ON to OFF, remaining
OFF for longer than 2 seconds (typical). The second is
“switch dimming action” in which the switch is toggled
from ON to OFF and back ON within 2 seconds
(typical).
When the device is in 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
external 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：
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 third 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
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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
Applications Examples for specific values.
DIM1
Floating
Floating
GND
GND
DIM2
Floating
GND
Floating
GND
Dimming levels
No Dimming
2 levels：100%-30%-100%
2 levels：100%-50%-100%
3 levels：100%-50%-20%-100%
When operating in switch dimming mode, 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
Linear Dimming
An external voltage, 0.5V to 2.5V, connected to the ADJ
pin can adjust the LED current. Two possible situations
might be used are：
If it is not possible to change the value of RCS to obtain
the desired value of LED current, an external voltage
reference can be connected to the ADJ pin to adjust the
voltage sense level across RCS, equivalent to changing
the value of RCS.
Connecting a resistor between the VIN and ADJ pin,
then connecting a thermistor from the ADJ pin to GND
can adjust the LED current based on temperature, thus
realizing the temperature compensation feature.
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 09/01/2011
5
datasheet pdf - http://www.DataSheet4U.net/
5 Page 
IS31LT3918
PACKAGE INFORMATION
SOP-8
Package Outline Drawing
#D08
5.10
4.70
0.25
0.17
1.27
0.40
6.20 4.00
5.80 3.80
0.25
0.10
1.55
1.35
0.51
0.33
1.27BSC
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1.75
1.35
8
0
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 09/01/2011
11
datasheet pdf - http://www.DataSheet4U.net/
11 Page | ||
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| PDF Descargar | [ Datasheet IS31LT3918.PDF ] | |
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