IS31LT3135V1, IS31LT3135V2
Dual Ch. (Main/Sub) LED Driver Evaluation Board Guide
Description
The IS31LT3135 is a dual‐channel LED driver that has two
modes of operation; it can function as the main‐channel
driver or as a sub‐channel source. When operating in main
mode, the device functions as a constant current source
that outputs an adjustable current, via an external resistor,
through the main LED. The device is operable with a
dropout voltage of 0.1V while driving a 200mA current.
When operating as a sub‐channel driver, the IC grounds the
LED’s cathode. The device normally operates with a single
channel powered on, allowing for quick switching between
the main and sub channel modes. A sweeping power
supply that operates between high and low voltages,
allows for simple switching between sub/main‐channel
modes, even during conditions where the UV pin is below
the 1.17V (typical) UV threshold IS31LT3135‐V1; or 1.23V
(typical) UV threshold for IS31LT3135‐V2. The sweeping
power supply allows sub‐channel to main channel
switching during conditions where the UV pin is
≥80mV
than the UV threshold. In addition, the main channel
features short protection via switching to sub‐channel if
any abnormal behaviors occur in the main‐channel LED
circuitry.
Quick Start
Figure 1: Photo of IS31LT3135V1/V2 evaluation board
Recommended Equipment
5VDC Power supply
1W LED
Multi‐meter
Recommended I/O Ratings
Power supply voltage: 3.8VDC
Output of I
MAIN
: 320mA per LED
Output of I
SUB
: 20mA per LED
Features
Power supply under‐voltage detection
Main‐channel LED short protection
Over‐temperature protection
Input voltage range: 2.7V to 5.5V
Main/sub‐channel adjustable output current
(Set via user‐configurable external resistors)
Main‐channel dropout VDP=0.1V
Ultra‐low quiescent current
SOP‐8 Package, small PCB footprint size
Note: When the power supply voltage ≥ LED voltage rating, extra voltage
is dissipated through the main‐channel, causing a drop in system
efficiency and an increase in wasted energy.
Absolute Maximum Ratings
Input voltage ≤ 5VDC
Caution: Do not exceed the input voltage conditions listed above to
avoid risking permanent damage to the board.
Ordering Information
Part Number
IS31LT3135‐V1GRLS2‐EB
IS31LT3135‐V2GRLS2‐EB
Temperature Range
−40°C to +85°C (Industrial Grade)
IC Package
SOP‐8 (5mm x 4mm)
Table 1: Ordering Information for IS31LT3135‐V1/V2 evaluation board.
Customers with inquiries regarding pricing, delivery, part availability, and related information, can
reach ISSI Analog marketing via either of the following methods:
Email: analog_mkt@issi.com
/
Phone: +1 (408) 969‐6600
Integrated Silicon Solution, Inc. –
http://www.issi.com
V2, 4/23/2012
1
IS31LT3135V1, IS31LT3135V2
Dual Ch. (Main/Sub) LED Driver Evaluation Board Guide
Procedure
The IS31LT3135 evaluation board comes assembled and equipped with the purpose of allowing the user to easily
demonstrate, or evaluate, functions of the IC driver. In order to verify device operation, please follow the listed directions
carefully.
Caution: When powering on the circuit; ensure that all connections are properly linked to complete the board circuitry.
1.
2.
3.
4.
5.
Connect the negative terminal of the power supply to the GND pin.
Connect the positive terminal of supply to the VCC pin.
Connect the negative end of the LED panel (LED arrays) to the LED− terminal.
Connect the positive end of the LED panel (LED arrays) to the LED+ terminal.
After ensuring connections are sound and that the circuit is complete, turn on the power supply to drive current
through the LED panel (LED arrays) and perform evaluation.
Figure 2: IS31LT3135 evaluation board circuit schematic.
Bill of Materials
Name
Capacitor
Description
10uF±20%,16V, Surface‐mount, 0805
100nF±20%,50V, Surface‐mount, 0603
51K±1%, Surface‐mount, 0805 (V1)
47K±1%, Surface‐mount, 0805 (V2)
30K±1%, Surface‐mount, 0805
30K±1%, Surface‐mount, 0805
33±1%, Surface‐mount, 0805
Schottky type, SS16,1A, 60V, SMA
IS31LT3135, SOP‐8 Package
Symbol
C1
C2
R1
R2
R3
R4
D1
U1
Quantity
1
1
1
1
1
1
1
1
2
Resistor
Diode
HBLED Driver IC
Table 2: IS31LT3135 Bill of Materials. Refer to Figure 2 for specific component locations
Integrated Silicon Solution, Inc. –
http://www.issi.com
V2, 4/23/2012
IS31LT3135V1, IS31LT3135V2
Dual Ch. (Main/Sub) LED Driver Evaluation Board Guide
Device Operation
MainChannel LED Output Current
The main‐channel LED current is adjusted by using a resistor connected to Iset pin. The voltage of Iset pin will remain at 1.2V,
independent of external factors including transient temperature and source voltage fluctuations. The through the
main‐channel LED is calculated by using the following equation:
I
MAIN
½
8000
V
SET
R
SET
The main‐channel current will continue through the LED to the GND pin. 0.1V dropout voltage occurs when the
main‐channel current is ≤ 200mA.
Sub‐channel LED current originates from the SUB terminal to ground, and likewise its corresponding LED current can be set
via an external resistor.
I
SUB
½
V
CC
V
F2
V
D2
R
4
R
SUB
V
CC
is the power supply voltage. V
F2
is the sub‐LED voltage. V
D2
denotes the diode voltage and its value should be minimized.
UV Threshold Configuration
The UV pin detects any voltage swings and compensates by utilizing 0.8v hysteresis. This form of error correction
mechanism will ensure reliable device operation, even when the power supply experiences an unwanted ripple effect.
Sweeping power supply from a high to low voltage, results in main channel switch to sub‐channel while UV pin is below the
UV threshold of 1.17V (IS31LT3135‐V1 typical) or 1.23V (IS31LT3135‐V2 typical.) Sweeping power supply from a low to high
voltage, will cause the sub‐channel mode to switch back to main‐channel operation, under conditions where UV pin is 80mV
higher than the UV threshold. U
uv
is set by the ratio of resistor R1 over resistor R2.
R
2
When
R
R
V
CC
½
1.17 V (V1) or 1.23V(V2)
; an immediate switch from main to sub‐channel operation
2
1
occurs. Lithium‐ion batteries typically maintain a voltage level of 3.7V during discharge, so the recommended UV threshold
is 3.4V. Typically resistors R1 and R2 are set to 10K magnitude（i.e.51k）Small resistance values for R1 and R2 will
translate to losses in heat or efficiency. To minimize these
losses, it is recommended to derive precise values for the
resistors so that the end device operates with the highest efficiency rate achievable.
ShortCircuit Protection Mechanism
When the main‐channel LED is shorted, IS31LT3135 will automatically switch to sub‐channel mode.
PCB layout reference
The switch should be placed in an area with low voltages, to avoid an instant spark while switching. The traces between
GND pin and I
SET
pin to real ground should be as short and wide as possible, with the purpose of improving the main LED
current accuracy and under voltage threshold accuracy. Adding a 0.1uF, capacitor may also help with this purpose.
Integrated Silicon Solution, Inc. –
http://www.issi.com
V2, 4/23/2012
3
IS31LT3135V1, IS31LT3135V2
Dual Ch. (Main/Sub) LED Driver Evaluation Board Guide
Figure 3: Component Placement: Top Layer Figure 4: PCB Layout‐ Top Layer
Figure 5: Component Placement Guide ‐Bottom Layer
Figure 6: Board PCB Layout‐Bottom Layer
Copyright© 2012 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. –
http://www.issi.com
V2, 4/23/2012
4
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