IS31LT3170/71

IS31LT3170/71
10-TO-150MA CONSTANT-CURRENT LED DRIVER
Preliminary Information
August 2015
GENERAL DESCRIPTION
FEATURES
The IS31LT3170 and IS31LT3171 are adjustable
linear current 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 a minimal voltage headroom of 0.6V.
Designed with a low dropout voltage; the device can
drive LED strings close to the supply voltage without
switch capacitors or inductors.

The IS31LT3170/71 simplifies designs by
providing a stable current without the additional
requirement of input or output capacitors,
inductors, FETs or diodes. The complete constant
current driver requires only a current set resistor
and a small PCB area making designs both
efficient and cost effective.


The EN Pin (1) of the IS31LT3171 can function as
the PWM signal input used for LED dimming
purposes.

As a current sink it is ideal for LED lighting
applications or current limiter for power supplies.


The device is provided in a lead (Pb) free, SOT23-6
package.



Low-side current sink
- Current preset to 10mA
- Adjustable from 10mA to 150mA with external
resistor selection
Wide input voltage range from
- 2.5V to 42V (IS31LT3171)
- 5V to 42V (IS31LT3170)
with a low dropout of 0.6V
Up to 10kHz PWM input (IS31LT3171 only)
Protection features:
- 0.26%/K negative temperature coefficient at
high temp for thermal protection
Up to 1W power dissipation in a small SOT23-6
package
RoHS compliant (Pb-free) package
APPLICATIONS

Architectural LED lighting
Channel letters for advertising, LED strips for
decorative lighting
Retail lighting in fridge, freezer case and
vending machines
Emergency lighting (e.g. steps lighting, exit way
sign etc.)
TYPICAL APPLICATION CIRCUIT
VIN
VIN
1
6
REXT
5.1Ω
EN
GND
2.5V~5.5V
or
4
IS31LT3170
REXT
OUT
1
PWM
6
2,3,5
REXT
5.1Ω
EN
GND
4
IS31LT3171
REXT
OUT
2,3,5
Figure 1 Typical Application Circuit
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PIN CONFIGURATION
Package
Pin Configuration (Top View)
SOT23-6
PIN DESCRIPTION
No.
Pin
Description
1
EN
Enable pin (PWM input IS31LT3171 only).
2,3,5
OUT
Current sink.
4
GND
Ground.
6
REXT
Optional current adjust.
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ORDERING INFORMATION
Industrial Range: -40°C to +125°C
Order Part No.
Package
QTY/Reel
IS31LT3170-STLS4-TR
IS31LT3171-STLS4-TR
SOT-23-6, Lead-free
3000
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. 0A, 08/04/2015 3 IS31LT3170/71
ABSOLUTE MAXIMUM RATINGS (Note 1)
Maximum enable voltage, VEN(MAX) only for IS31LT3170-STLS4-TR
VEN(MAX) only for IS31LT3171-STLS4-TR
Maximum output current, IOUT(MAX)
Maximum output voltage, VOUT(MAX)
Reverse voltage between all terminals, VR
Junction to ambient, θJA
Power dissipation, PD(MAX) (Note 2)
Maximum junction temperature, TJMAX
Storage temperature range, TSTG
Operating temperature range, TA
ESD (HBM)
ESD (CDM)
45V
6V
200mA
45V
0.5V
94.8°C/W
1W
150°C
-65°C ~ +150°C
−40°C ~ +125°C
2kV
500V
Note 1:
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only
and functional operation of the device at these or any other condition beyond those indicated in the operational sections of the specifications is
not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Note 2:
Detail information please refer to package thermal de-rating curve on Page 13.
ELECTRICAL CHARACTERISTICS
“●” This symbol in the table means these parameters are for IS31LT3170-STLS4-TR.
“○” This symbol in the table means these parameters are for IS31LT3171-STLS4-TR.
Test condition is TA = TJ = 25°C, unless otherwise specified.
Symbol
VBD_OUT
Parameter
OUT pin breakdown voltage
IEN
Enable current
RINT
Internal resistor
IOUT
Output current
Condition
Min.
VEN= 0V
Typ.
Max.
42
V
VEN= 24V
●
0.35
VEN= 3.3V
○
0.35
IRINT = 10mA
mA
100
106
112
9
10
11
VOUT = 1.4V, VEN = 24V,
REXT OPEN
●
VOUT = 1.4V, VEN = 3.3V,
REXT OPEN
○
9
10
11
VOUT > 2.0V, VEN = 24V,
REXT = 10Ω
●
110
116
122
VOUT > 2.0V, VEN = 3.3V,
REXT = 10Ω
○
110
116
122
Integrated Silicon Solution, Inc. – www.issi.com Rev. 0A, 08/04/2015 Unit
Ω
mA
mA
4 IS31LT3170/71
DC CHARACTERISTICS WITH STABILIZED LED LOAD
“●” This symbol in the table means these parameters are for IS31LT3170-STLS4-TR.
“○” This symbol in the table means these parameters are for IS31LT3171-STLS4-TR.
Test condition is TA = TJ = 25°C, unless otherwise specified.
Symbol
Parameter
VS
Sufficient supply voltage on EN
pin
VHR
Lowest sufficient headroom
voltage on OUT pin
Output current change versus
ambient temp change
∆IOUT/IOUT
(Note 3)
Output current change versus
Vout
Condition
Min.
Typ.
Max.
●
5
42
○
2.5
5.5
IOUT = 100mA
0.6
1
VOUT > 2.0V, VEN = 24V,
REXT = 10Ω
●
VOUT > 2.0V, VEN = 3.3V,
REXT = 10Ω
○
-0.26
VOUT > 2.0V, VEN = 24V,
REXT = 10Ω
●
1.9
VOUT > 2.0V, VEN = 3.3V,
REXT = 10Ω
○
1.9
Unit
V
V
-0.26
%/K
%/V
Note 3: Guaranteed by design.
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FUNCTIONAL BLOCK DIAGRAM
IS31LT3170
IS31LT3171
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TYPICAL PERFORMANCE CHARACTERISTICS
IS31LT3170
80
VEN = 42V
REXT = 20Ω
VEN = 42V
REXT Open
25
Output Current (mA)
Output Current (mA)
30
20
15
TA = 85°C
TA = 25°C
10
TA = 125°C
0
0.5
2
3.5
5
6.5
8
9.5
11
12.5
60
TA = 125°C
TA = 85°C
40
0
0.5
14
2
3.5
5
6.5
8
9.5
11
12.5
14
Output Voltage (V)
Output Voltage (V)
Figure 3 IOUT vs. VOUT
Figure 2 IOUT vs. VOUT
180
150
VEN = 42V
REXT = 7.5Ω
160
TA = 25°C
TA = -40°C
Output Current (mA)
VEN = 42V
REXT = 10Ω
Output Current (mA)
TA = -40°C
20
TA = -40°C
5
TA = 25°C
100
TA = 85°C
TA = 125°C
50
TA = 25°C
TA = -40°C
140
TA = 85°C
120
100
80
TA = 125°C
60
40
20
0
0.5
2
3.5
5
6.5
8
9.5
11
12.5
0
0.5
14
2
3.5
5
Output Voltage (V)
Figure 4 IOUT vs. VOUT
9.5
11
12.5
14
Figure 5 IOUT vs. VOUT
200
VEN = 5V
fPWM = [email protected]1% Duty Cycle
TA = 25°C
160
REXT = 10Ω
140
120
100
REXT= 20Ω
80
60
40
VEN = 42V
TA = 25°C
180
REXT = 7.5Ω
Output Current (mA)
180
Output Current (mA)
8
Output Voltage (V)
200
160
140
REXT = 7.5Ω
REXT = 10Ω
120
100
REXT = 20Ω
80
60
40
REXT Open
20
0
6.5
REXT Open
20
0
2
4
6
8
10
12
Output Voltage (V)
Figure 6 IOUT vs. VOUT
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0
0
2
4
6
8
10
12
14
Output Voltage (V)
Figure 7 IOUT vs. VOUT
7 IS31LT3170/71
80
20
VOUT = 2V
REXT = 20Ω
16
TA = 25°C
12
8
Output Current (mA)
Output Current (mA)
VOUT = 2V
REXT Open
TA = 85°C
TA = 125°C
TA = -40°C
TA = 25°C
TA = 85°C
60
TA = -40°C
TA = 125°C
40
20
4
0
5
15
25
0
42
35
5
15
25
VEN (V)
42
VEN (V)
Figure 8 IOUT vs. VEN
Figure 9 IOUT vs. VEN
150
200
TA = 85°C
120
90
TA = -40°C
TA = 125°C
VOUT = 2V
REXT = 7.5Ω
175
TA = 25°C
Output Current (mA)
VOUT = 2V
REXT = 10Ω
Output Current (mA)
35
60
TA = 25°C
TA = 85°C
150
125
TA = -40°C
TA = 125°C
100
75
50
30
25
0
5
15
25
35
0
42
5
15
25
VEN (V)
Figure 11 IOUT vs. VEN
Figure 10 IOUT vs. VEN
REXT = 7.5Ω
IOUT = 0A
REXT Open
TA = -40°C
400
Supply Current (µA)
Output Current (mA)
500
VOUT = 2V
TA = 25°C
140
REXT = 10Ω
120
100
80
REXT = 20Ω
60
40
TA = 25°C
300
TA = 85°C
200
TA = 125°C
100
REXT Open
20
0
0
42
VEN (V)
180
160
35
5
10
15
20
25
30
35
VEN (V)
Figure 12 IOUT vs. VEN
Integrated Silicon Solution, Inc. – www.issi.com Rev. 0A, 08/04/2015 40 42
0
0
5
10
15
20
25
30
35
40 42
VEN (V)
Figure 13 IEN vs. VEN
8 IS31LT3170/71
250
Output Current (mA)
VEN = 42V
VOUT = 2V
200
150
100
50
0
1
10
100
REXT (Ω)
Figure 14 IOUT vs. REXT
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IS31LT3171
80
VEN = 3.3V
REXT = 20Ω
VEN = 3.3V
REXT Open
25
Output Current (mA)
Output Current (mA)
30
20
15
TA = 25°C
TA = 85°C
10
TA = -40°C
TA = 25°C
60
TA = 85°C
TA = 125°C
40
20
TA = 125°C
5 TA = -40°C
0
0.5
2
3.5
5
6.5
8
9.5
11
12.5
0
0.5
14
2
3.5
5
9.5
11
12.5
14
Figure 16 IOUT vs. VOUT
Figure 15 IOUT vs. VOUT
180
150
VEN = 3.3V
REXT = 7.5Ω
160
TA = 25°C
TA = -40°C
Output Current (mA)
Output Current (mA)
8
Output Voltage (V)
Output Voltage (V)
VEN = 3.3V
REXT = 10Ω
6.5
100
TA = 85°C
TA = 125°C
50
TA = 25°C
TA = -40°C
140
120
TA = 85°C
100
80
TA = 125°C
60
40
20
0
0.5
2
3.5
5
6.5
8
9.5
11
12.5
0
0.5
14
2
3.5
5
Output Voltage (V)
Output Current (mA)
Output Current (mA)
120
100
REXT= 20Ω
60
40
14
160
REXT = 7.5Ω
140
REXT = 10Ω
120
100
REXT = 20Ω
80
60
40
REXT Open
REXT Open
20
0
12.5
VEN = 3.3V
TA = 25°C
180
REXT = 10Ω
80
11
200
REXT = 7.5Ω
160
140
9.5
Figure 18 IOUT vs. VOUT
VEN = 5V
fPWM = [email protected]% Duty Cycle
TA = 25°C
180
8
Output Voltage (V)
Figure 17 IOUT vs. VOUT
200
6.5
20
0
2
4
6
8
10
12
Output Voltage (V)
Figure 19 IOUT vs. VOUT
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0
0
2
4
6
8
10
12
14
Output Voltage (V)
Figure 20 IOUT vs. VOUT
10 IS31LT3170/71
80
20
VOUT = 2V
REXT = 20Ω
16
12
TA = 25°C
8
Output Current (mA)
Output Current (mA)
VOUT = 2V
REXT Open
TA = 85°C
TA = 125°C
TA = -40°C
TA = 25°C
TA = 85°C
60
TA = 125°C
TA = -40°C
40
20
4
0
0
2.5
3
3.5
4
4.5
5
2.5
3
3.5
4.5
5
VEN (V)
VEN (V)
Figure 22 IOUT vs. VEN
Figure 21 IOUT vs. VEN
200
150
VOUT = 2V
REXT = 10Ω
TA = 85°C
120
90
TA = 25°C
TA = -40°C
TA = 125°C
VOUT = 2V
REXT = 7.5Ω
175
Output Current (mA)
Output Current (mA)
4
60
TA = 25°C
TA = -40°C
150
125
TA = 85°C
TA = 125°C
100
75
50
30
25
0
2.5
3
3.5
4
4.5
0
5
2.5
3
3.5
500
REXT = 7.5Ω
VOUT = 2V
TA = 25°C
IOUT = 0A
REXT Open
400
140
Supply Current (µA)
Output Current (mA)
5
Figure 24 IOUT vs. VEN
Figure 23 IOUT vs. VEN
180
REXT = 10Ω
120
100
REXT = 20Ω
80
60
40
TA = -40°C
TA = 25°C
300
200
TA = 85°C
TA = 125°C
100
REXT Open
20
0
4.5
VEN (V)
VEN (V)
160
4
2.5
3
3.5
4
4.5
5
0
0.5
1
1.5
2
2.5
3
VEN (V)
VEN (V)
Figure 25 IOUT vs. VEN
Figure 26 IEN vs. VEN
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4
4.5
11 5
IS31LT3170/71
250
Output Current (mA)
VEN = 3.3V
VOUT = 2V
200
150
100
50
0
1
10
100
REXT (Ω)
Figure 27 IOUT vs. REXT
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APPLICATIONS INFORMATION
IS31LT3170/71 provides an easy constant current
source 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 
(1)
REXT
Where RINT (106Ω typ) is an 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 IS31LT3170/71.
HIGH INPUT VOLTAGE APPLICATION
When driving a long string of LEDs whose total
forward voltage drop exceeds the IS31LT3170
VBD_OUT limit of 42V, it is possible to stack several
LEDs(such as 2 LEDs) between the EN pin and the
OUT pins 2,3, and 5 so the voltage on the EN pin is
higher than 5V. The remaining string of LEDs can
then be placed between power supply +VS and EN
pin, (Figure 3). The number of LEDs required to
stack at EN pin will depend on the LED’s forward
voltage drop (VF) and the +VS value.
When operating the chip at high ambient
temperatures, or when driving maximum load
current, care must be taken to avoid exceeding the
package power dissipation limits. Exceeding the
package dissipation will cause the device to enter
thermal protection mode. The maximum package
power dissipation can be calculated using the
following Equation (2):
PD ( MAX ) 
TJ ( MAX )  TA
(2)
 JA
Where TJ(MAX) is the maximum junction temperature,
TA is the ambient temperature, and θJA is the junction
to ambient thermal resistance; a metric for the
relative thermal performance of a package.
The recommended maximum operating junction
temperature, TJ(MAX), is 125°C and so the maximum
ambient temperature is determined by the package
parameter; θJA. The θJA for the IS31LT3170/71
SOT23-6 package, is 94.8°C/W.
Therefore the maximum power dissipation at TA =
25°C is:
PD ( MAX ) 
125C  25C
 1W
94.8C / W
The actual power dissipation PD is:
PD  VOUT  ( I EN  I OUT )
(3)
To ensure the performance, the die temperature (TJ)
of the IS31LT3170/71 should not exceed 125°C. The
graph below gives details for the package power
derating.
1.2
Note: when operating the IS31LT3170 at voltages
exceeding the device operating limits, care needs to
be taken to keep the EN pin and OUT pin voltage
below 42V.
THERMAL PROTECTION AND DISSIPATION
The IS31LT3170/71 implements thermal foldback
protection to reduce the LED current when the
package’s thermal dissipation is exceeded and
prevent “thermal runaway”. The thermal foldback
implements a negative temperature coefficient
(NTC) of -0.26%/K.
Integrated Silicon Solution, Inc. – www.issi.com Rev. 0A, 08/04/2015 Power Dissipation (W)
Figure 28 High Input Voltage Application Circuit
SOT23-6
1
0.8
0.6
0.4
0.2
0
-40
-25
-10
5
20
35
50
65
80
95
110 125
Temperature (°C)
Figure 29 PD vs. TA (SOT23-6)
13 IS31LT3170/71
The thermal resistance is achieved by mounting the
IS31LT3170/71 on a standard FR4 double-sided
printed circuit board (PCB) with a copper area of a
few square inches on each side of the board under
the IS31LT3170/71. Multiple thermal vias, as shown
in Figure 5, help to conduct the heat from the
exposed pad of the IS31LT3170/71 to the copper on
each side of the board. The thermal resistance can
be reduced by using a metal substrate or by adding
a heatsink.
Figure 30 Board Via Layout For Thermal Dissipation
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CLASSIFICATION REFLOW PROFILES
Profile Feature
Preheat & Soak
Temperature min (Tsmin)
Temperature max (Tsmax)
Time (Tsmin to Tsmax) (ts)
Pb-Free Assembly
150°C
200°C
60-120 seconds
Average ramp-up rate (Tsmax to Tp)
3°C/second max.
Liquidous temperature (TL)
217°C
Time at liquidous (tL)
60-150 seconds
Peak package body temperature (Tp)*
Max 260°C
Time (tp)** within 5°C of the specified
classification temperature (Tc)
Max 30 seconds
Average ramp-down rate (Tp to Tsmax)
6°C/second max.
Time 25°C to peak temperature
8 minutes max.
Figure 31 Classification Profile
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PACKAGE INFORMATION
SOT23-6
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RECOMMENDED LAND PATTERN
Note:
1. Land pattern complies to IPC-7351.
2. All dimensions in MM.
3. This document (including dimensions, notes & specs) is a recommendation based on typical circuit board manufacturing parameters. Since
land pattern design depends on many factors unknown (eg. user’s board manufacturing specs), user must determine suitability for use.
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