IS31LT3380
40V/1.2A LED DRIVER WITH SWITCH DIMMING
OCTOBER 2011
GENERAL DESCRIPTION
The IS31LT3380 is a continuous mode inductive
step-down converter, designed for driving a single LED or
multiple series connected LEDs efficiently from a voltage
source higher than the LED voltage. The chip operates
from an input voltage between 8.5V and 40V and
provides an output current up to 1.2A.
The IS31LT3380 includes a high-side output current
sensing circuit, which uses an external resistor to set the
nominal average output current. The IS31LT3380
includes an integrated output switch which has a very low
conducting impedance to ensure high system efficiency.
The IS31LT3380 has switch dimming function. The chip
detects external switch action to adjust output current,
allowing for dimming functionality to be achieved without
changing the original lighting system circuitry.
The switch dimming is implemented in either two-level
mode or three-level mode. The output current of every
level and the total number of levels are customer
selected by setting the corresponding input conditions of
DIM1 and DIM2 pin.
The output current is set at the initial value the first time
that power is supplied to the chip. After the initial power
up sequence, the chip adjusts the output current
according to the external switch action. After the lowest
current level, the current cycles back to the initial value if
more switch action is detected. If the power is switched
off for longer than 2 seconds, the device will return to it’s
initial state, and the output current will be set to the initial
value at the next time that power is applied.
FEATURES
Multi-modes switch dimming
Up to 1.2A output current
High efficiency (up to 98%)
Wide input voltage range: 8.5V to 40V
Internal 40V power switch
Simple low parts count
Typical 5% output current accuracy
Up to 1MHz switching frequency
Inherent LED open-circuit/short-circuit protection
Thermal shutdown protection circuitry
SOP8 package
APPLICATIONS
MR16, MR11 LED spotlight
LED street lighting
PAR LED bulb
Other LED lighting
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
IS31LT3380
PIN CONFIGURATIONS
Package
Pin Configurations
SOP-8
PIN DESCRIPTION
Pin Name
V
IN
I
SENSE
DIM1
NO.
1
2
6
Description
Input voltage (8.5V to 40V). Decouple to ground with 0.1μF X7R ceramic capacitor close to device. While
using the switch dimming function, connect a 220Uf or higher capacitor close the device.
Connect resistor R
S
from this pin to V
IN
to define nominal average output current I
OUTnom
=0.1/R
S
Set the current-levels number of and current ratio of each level of switch dimming function as below:
DIM1=“floating” DIM2=“floating”，not dimming；
DIM1=“floating” DIM2=“GND”，three-levels，100%---50%---20%；
DIM2
GND
LX
NC
5
7
8
3,4
DIM1=“GND” DIM2=“floating”，three-levels，100%---60%---30%；
DIM1=“GND” DIM2=“GND”，two-levels，100%---30%。
Ground (0V)
Drain of power switch
Not connect. Float required
ORDERING INFORMATION
Industrial Range: -40°C to 105°C
Order Number
IS31LT3380-GRLS3-TR
Package
SOP-8, Lead-free
QTY/Reel
2500
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 09/01/2011
3
IS31LT3380
ABSOLUTE MAXIMUM RATINGS (NOTE1)
Symbol
V
IN
V
ISENSE
V
LX
V
DIM
I
LX
P
tot
T
OP
T
ST
T
j MAX
R
θJA
Parameter
Input voltage
I
SENSE
voltage
LX output voltage
DIM1 ,DIM2 pin input voltage
Switch output current
Power dissipation
Operating temperature
Storage temperature
Junction temperature
Junction to ambient
ESD Rating (HBM)
Rating
-0.3V to +50V
Vin+0.3V to Vin-5V ,Vin>5V
Vin+0.3V to -0.3V,Vin<5v
-0.3V to +50V
-0.3V to +6V
1.5A
0.5W
-40 °C to 105°C
-55 to 150°C
150°C
100°C/W
3kV
ELECTRICAL CHARACTERISTICS
(V
IN
=12V, T
A
=25°C unless otherwise stated) (NOTE 2)
Symbol
V
IN
I
INQoff
I
INQon
Parameter
Input voltage
Quiescent supply current with
output off
Quiescent supply current with
output switching
Mean current sense threshold
voltage
Undervoltage lockout threshold
Undervoltage lockout hysteresis
Sense threshold hysteresis
I
SENSE
pin input current
the interval time between the
external switch action
In dimming mode 1,the ratio of
different output current level to the
initial current (DIM1=“floating”
DIM2=“GND”)
Level 1
Level 2
Level 3
17%
V
SENSE
=V
IN
-0.1
V
IN
falling
95
Conditions
Min.
8.5
70
120
450
Typ.
Max.
40
140
600
Unit
V
μA
μA
V
ISENSE
100
105
mV
UVLO
△
UVLO
5.05
5.85
1.65
±15
8
2
100%
50%
20%
6.65
V
V
%
μA
S
V
SENSEHYS
I
SENSE
Ts
Kmode1
23%
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 09/01/2011
4
IS31LT3380
ELECTRICAL CHARACTERISTICS
(V
IN
=12V, TA=25°C unless otherwise stated) (NOTE 2) (continued)
Symbol
Parameter
In dimming mode 2,the ratio of
different output current level to
the initial current (DIM1=“GND”
DIM2=“floating”)
In dimming mode 3,the ratio of
different output current level to
the initial current (DIM1=“GND”
DIM2=“GND”)
Continuous LX switch current
LX switch leakage current
LX Switch ‘On’ resistance
Minimum switch ‘ON’ time
Minimum switch ‘OFF’ time
Recommended maximum
operating frequency
Internal comparator propagation
delay
Thermal shutdown temperature
Thermal shutdown hysteresis
25
150
20
LX switch ‘ON’
LX switch ‘OFF’
0.3
200
200
1
Conditions
Level 1
Level 2
Level 3
Level 1
Level 2
28%
28%
Min.
Typ.
100%
60%
30%
100%
30%
1.2
1
0.4
32%
A
μA
Ω
ns
ns
MHz
ns
°C
°C
32%
Max.
Unit
Kmode2
Kmode3
I
LXmean
I
LX(leak)
R
LX
T
ONmin
T
OFFmin
f
LXmax
T
PD
T
SD
T
SD-HYS
NOTES:
1. Work beyond maximum absolute voltage and current will cause permanent damage to the device. Long time working under absolute conditions
will lower the reliability of the dice.
2. Production testing of the chip is performed at 25°C. Functional operation of the chip and parameters specified are guaranteed by design,
characterization and process control in other temperature.
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 09/01/2011
5
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