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PDF IS31LT3938 Data sheet ( Hoja de datos )
| Número de pieza | IS31LT3938 | |
| Descripción | High Voltage LED Lighting Driver | |
| Fabricantes | ISSI | |
| Logotipo |  |
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IS31LT3938
Preliminary
High Voltage LED Lighting Driver with Three Level Power Sequencing
General 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 three
power sequencing levels 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 level to the next step.
As a result, the input and output power of the luminaire
may be adjusted depending on the desired amount of
illumination and/or power consumption. There are
multiple power levels that the engineer may configure,
2 steps or 3 steps, via the external pins DIM1 and
DIM2.
IS31LT3938 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.
IS31LT3938 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 power sequencing levels
3% output current accuracy
Over current, temperature protection and short circuit
protection
High efficiency (typical up to 95%)
Higher MOS drive voltage
Wide input voltage range: 10VDC~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
D2 RIN
AC Input
Fuse
D3
C1
CIN
D4
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D5
C3
IS3938
VIN
DIM1
Gate
CS
DIM2
GND
ADJ
TOFF
REXT
L1
Q1
RCS
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
R0.1, 04/25/2012
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datasheet pdf - http://www.DataSheet4U.net/
1 page  
IS31LT3938
Preliminary
Oscillator
IS31LT3938’s TOFF pin controls the off time of the
is no switchable power levels, and the output
current is 100% of the programmed value when the
internal oscillator. Oscillator off time is determined by
power is on.
the following equation:
Toff (s) 40 1012 REXT
REXT：resistor connected between TOFF and GND
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%.
Switchable Power Levels
IS31LT3938 detects the external switch action of the
c) A second power sequencing action causes the
current to return to 100%.
main power switch, and can automatically adjust the
d) A third power sequencing action has the same
level of the output current based on the action of the
main power switch.
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
dimming sequence is as described in (2) above,
except that the current sequence is
100%-50%-100%.
The action of the external power switch can be divided
into two types. The first is “normal switch operation”
4. When both DIM1 and DIM2 are connected to GND,
the dimming sequence is as described in (2) above,
wherein the switch is toggled from ON to OFF,
except that the current sequence is
remaining OFF for longer than 4 seconds (typical). The
other is “power sequencing action” wherein the switch
100%-50%-20%-100%.
If the switch is operated normally, that is, switched on
is toggled from ON to OFF and back ON within 4
seconds (typical).
When the device experiences normal switch operation,
once after being in the OFF position for a long time, or if
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both the DIM1 and DIM2 pins are floating, then the
output current always starts up at the initial value of
it merely powers on in the first state, 100%, when the
power switch is toggled to ON, and the device turns off
100%.
Note: Because the main power switch is used to initiate
when the external power switch is changed to OFF.
the power sequencing function, the device must have a
Power sequencing output current levels are configured
by connecting the DIM1 and DIM2 pins as indicated in
large enough external capacitor on VIN to maintain
device operation for 4 seconds.
the table below：
DIM1
Floating
Floating
GND
GND
DIM2
Floating
GND
Floating
GND
Power sequencing levels
No Power Sequencing
2 levels：100%-30%-100%
2 levels：100%-50%-100%
3 levels：100%-50%-20%-100%
Linear Dimming
An external voltage, 0.5V to 2.5V, connected to the ADJ
pin can adjust the LED current. Two possible situations
where this 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
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
Integrated Silicon Solution, Inc. – www.issi.com
R0.1, 04/25/2012
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.
5
datasheet pdf - http://www.DataSheet4U.net/
5 Page 
IS31LT3938
Package Information
SOP-8
Preliminary
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
R0.1, 04/25/2012
11
datasheet pdf - http://www.DataSheet4U.net/
11 Page | ||
| Páginas | Total 11 Páginas | |
| PDF Descargar | [ Datasheet IS31LT3938.PDF ] | |
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