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PDF IS31LT3135 Data sheet ( Hoja de datos )
| Número de pieza | IS31LT3135 | |
| Descripción | MAIN/SUB DUAL-CHANNEL LED DRIVER | |
| Fabricantes | ISSI | |
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IS31LT3135
MAIN/SUB DUAL-CHANNEL LED DRIVER
GENERAL DESCRIPTION
IS31LT3135 is a main/sub dual-channel LED driver.
When the main channel works，it is a constant current
source driving the main LED and the current is set by
an external resistor connected to the ISET pin. It needs
only 0.1v dropout voltage for 200mA output current.
When the sub-channel works, the chip will pull down
the sub LED’s cathode to ground.
Normally there is only one channel on, the main
channel and the sub channel can switch between each
other. Sweeping power supply from high voltage to low
voltage, main channel switches to sub-channel while
UV pin is below the undervoltage threshold 1.17V
(IS31LT3135-V1 typical) or 1.23V (IS31LT3135-V2
typical). Sweeping power supply from low voltage to
high voltage, the sub-channel switches to the main
channel while UV pin is 80mV (typical) higher than the
undervoltage threshold. Additionally, the main channel
has short protection function, when the main LED is
shorted，the chip will switch to sub-channel
automatically.
FEATURES
November 2011
Power supply undervoltage detect
Main channel short protection
Over-temperature protection
Input voltage range: 2.7V~5.5V
Main and sub-channel current set by external
resistor
Main channel Vdp=0.1V
Low quiescent current
Assembled in SOP-8 package
APPLICATIONS
Miner lamp
Other LED lighting
TYPICAL APPLICATION CIRCUIT
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IS31LT3135
Figure 1
.
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, 11/08/2011
1
datasheet pdf - http://www.DataSheet4U.net/
1 page  
IS31LT3135
APPLICATION NOTES
MAIN LED CURRENT SET
Current of the main LED is set by resistor connected to
Iset pin. Voltage of Iset pin is 1.2V. It is constant
even if the environment temperature and power supply
voltage changes.(Refer to figure2, figure3). The
current of main channel is 8000 times to the current of
Iset pin. It is obtained by:
I main
8000 * Vset
Rset
Main LED current flows through the MAIN pin to
ground. There is only 0.1V voltage dropout when the
main channel current is 200mA (Note 1).
SUB LED CURRENT SET
Sub-LED current flows through SUB to ground. This
current can be set by the resistor of SUB pin and is
given by:
I sub
VCC
VF2 Vd2
R SUB
VCC is power supply voltage, VF2 is the sub-LED
voltage. Vd2 is the diode voltage（Refer to Figure 1），
its value should be as small as possible.
UNDERVOLTAGE THRESHOLD SET
UV pin has undervoltage detect function and the
undervoltage threshold gets a 0.8V hysteresis to avoid
error operation caused by power supply ripple.
Sweeping power supply from high voltage to low
voltage, the main channel switches to sub-channel
while UV pin is below undervoltage threshold, 1.17V
(IS31LT3135-V1 typical) or 1.23V (IS31LT3135-V2
typical). Sweeping power supply from low voltage to
high voltage, the sub-channel switches to the main
channel while UV pin is 80mV (typical) higher than the
undervoltage threshold. Uuv is set by the ratio of
resistor of R1 and R2 (Refer to Figure1).
When
R2
R1 R2
VCC
=1.17V
or
1.23V,
chip
switches
from the main channel to the sub-channel.
Typically，Li battery voltage maintains at 3.7V during
discharge. Therefore, it is recommended to set the
undervoltage threshold at 3.4V.
Typically, R1 and R2 are set to 10K Ohm magnitude
（e.g. 51K Ohm）, the current flows through R1 and R2
is large if the value of R1 and R2 are small, which will
reduce system efficiency. We can specify the value of
R2, and then calculate the value of R1 based on the
ratio.
MAIN LED SHORT PROTECTION
When the main LED is short circuit, chip will switch to
sub-channel automatically.
OVER-TEMPERATURE PROTECTION
When the chip temperature reaches 160℃, the chip
turns off automatically. When temperature drops back
to 140℃, the chip turns on again.
PCB LAYOUT REFERENCE
The switch should be placed at the low voltage point
(Refer to Figure 1) to avoid an instant spark while
switching. The traces between GND pin and Iset pin to
real ground should be as short as possible and as wide
as possible to improve the main LED current accuracy
and undervoltage threshold accuracy. Adding a 0.1uF
capacitor connected to UV pin can reduce the noise
pick-up at this pin.
http://www.DataSheet4U.net/
Note 1: When power supply voltage is larger than LED voltage, the
extra voltage would be added on the Main pin, which will reduce the
efficiency of the whole system.
Integrated Silicon Solution, Inc. — www.issi.com
Rev.A, 11/08/2011
5
datasheet pdf - http://www.DataSheet4U.net/
5 Page | ||
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