Demo Guide

IS31LT3171 10-TO-150mA CONSTANT-CURRENT LED DRIVER
DESCRIPTION
RECOMMENDED EQUIPMENT
The IS31LT3171 is adjustable constant current linear
devices with excellent temperature stability. A single
resistor is all that is required to set the operating
current from 10mA to 150mA. The devices can operate
from an input voltage from 2.5V to 42V with minimal
voltage headroom of 0.6V. Designed with a low
dropout voltage; the device can drive LED strings
close to the supply voltage.


As a current sink, it is ideal for LED lighting
applications or as power supply current limiters.
FEATURES





Low-side current sink
- Current preset to 10mA
- Adjustable from 10mA to 150mA with external
resistor selection
Wide input voltage: 2.5V to 42V
Up to 1W power dissipation in a small SOT23-6
package
RoHS compliant (Pb-free) package
Operating temperature range from -40°C ~ +125°C
42V, 500mA DC variable power supply
3 HBLEDs connected as a serial string
ABSOLUTE MAXIMUM RATINGS

≤ 42V input voltage
Caution: Do not exceed the conditions listed above, otherwise
the board will be damaged.
PROCEDURE
The IS31LT3171 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.
1)
2)
QUICK START
Connect the ground terminal of the power supply
to the GND (TP3) and the positive terminal to the
VCC (TP1). Connect the Anode of an external
LED string to LED+ (TP4) and its Cathode to LED(TP5).
The evaluation board supports eight current levels,
selected by JP1, JP2, JP3, see table below. The
test point REXT can be used to add an external
resistor. The final resistance can be measured
with an ohm meter across REXT and GND (TP6)
pins. For jumpers (JP1~JP3) Closed=1 and
Open=0.
Figure 1: Photo of IS31LT3171 Evaluation Board
3)
JP1
JP2
JP3
REXT (Ω)
0
0
0
-
0
0
1
100
0
1
0
15
0
1
1
13
1
0
0
8.2
1
0
1
7.6
1
1
0
5.3
1
1
1
5.0
The 0Ω resistor R4 must be NC. Otherwise, the
EN pin may be damaged by high voltage.
ORDERING INFORMATION
Part No.
Temperature Range
Package
IS31LT3171-STLS4-EB
-40°C ~ +125°C (Industrial)
SOT-23-6, Lead-free
Table 1: Ordering Information
For pricing, delivery, and ordering information, please contact ISSI’s analog marketing team at
analog@issi.com or (408) 969-6600
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 07/07/2015
1
IS31LT3171 10-TO-150mA CONSTANT-CURRENT LED DRIVER
EVALUATION BOARD OPERATION
IS31LT3171 evaluation board drives one string of
WLEDs. There are three resistors used for adjusting
the output current.
OUTPUT CURRENT SETTING
IS31LT3171 provides an easy constant current sink
solution for LED lighting applications. It uses an
external resistor to adjust the LED current from 10mA
to 150mA. The LED current can be determined by the
Equation (1):
I SET  10mA 
RINT  REXT 
Where RINT (106Ω, Typ.) is the device internal resistor
and REXT is the external resistor.
Paralleling a low tolerance resistor REXT with the
internal resistor RINT will improve the overall accuracy
of the current sense resistance. The resulting output
current will vary slightly lower due to the negative
temperature coefficient (NTC) resulting from the self
heating of the IS31LT3171.
(1)
REXT
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 07/07/2015
2
IS31LT3171 10-TO-150mA CONSTANT-CURRENT LED DRIVER
VCC
LED+
2
1
1
2
TP1
TP4
LEDU1
2
R4
3
5
1
2
TP5
OUT
REXT
OUT
OUT
REXT
6
JP1
JP2
JP3
EN
R1
2
1
1
EN
GND
TP2
R2
R3
4
IS31LT3171
GND
GND
2
1
1
2
TP3
TP6
Figure 2: IS31LT3171 Application Schematic
BILL OF MATERIALS
Name
Symbol
LED Driver
U1
Resistor
Description
Qty
Supplier
Part No.
LED Driver
1
ISSI
IS31LT3171
R1
RES,8R2,1/10W,±1%,SMD
1
YAGEO
RC0805FR-078R2L
Resistor
R2
RES,15R,1/10W,±1%,SMD
1
YAGEO
RC0805FR-0715RL
Resistor
R3
RES,100R,1/10W,±1%,SMD
1
YAGEO
RC0805JR-07100RL
Resistor
R4
Not installed
Jumper
JP1~JP3
Jumper
3
Test Terminal
TP1~TP6
Test terminal
6
Bill of materials, refer to Figure 2 above.
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 07/07/2015
3
IS31LT3171 10-TO-150mA CONSTANT-CURRENT LED DRIVER
0
0
1
2
1
2
1
2
1
2
1
2
1
1
1
1
2
2
2
1
2
0
0
Figure 3: Board Component Placement Guide - Top Layer
Figure 4: Board PCB Layout - Top Layer
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 07/07/2015
4
IS31LT3171 10-TO-150mA CONSTANT-CURRENT LED DRIVER
0
0
1
2
1
2
1
2
1
2
1
2
1
1
1
1
2
2
2
1
2
0
0
Figure 5: Board Component Placement Guide - Bottom Layer
Figure 6: Board PCB Layout - Bottom Layer
Copyright © 2015 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, 07/07/2015
5