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PDF IS31LT3352 Data sheet ( Hoja de datos )
| Número de pieza | IS31LT3352 | |
| Descripción | 40V LED DRIVER | |
| Fabricantes | ISSI | |
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IS31LT3352
40V LED DRIVER WITH TEMPERATURE COMPENSATION
OCTOBER 2011
GENERAL DESCRIPTION
The IS31LT3352 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 required LED voltage. The chip
operates from an input supply between 6V and 40V and
provides an externally adjustable output current of up to
750mA. Depending upon supply voltage and external
components, this can provide up to 30 watts of output
power.
The IS31LT3352 includes an integrated output switch
and a high-side output current sensing circuit, which uses
an external resistor to set the nominal average output
current.
The IS31LT3352 integrates temperature compensation
function in order to maintain LEDs’ stable and reliable
operation. The IS31LT3352 measures the thermistance
mounted close to LEDs. When ambient temperature near
LEDs goes too high and the Negative Temperature
Coefficient thermistors reach the value of threshold
resistance connected at RTH pin, output current starts to
reduce automatically. After the ambient temperature falls
down to a safe temperature，the current will return to the
set value.
The IS31LT3352 can be connected as LED drivers’ chain
with the same temperature compensation percentage. In
this chain, every IS31LT3352’s ADJO output pin drives
next stage’s IS31LT3352 ADJI input pin with temperature
compensation information. So, only one thermistor is
needed in the whole IS31LT3352 system.
FEATURES
Simple low parts count
Internal 40V power switch
Wide input voltage range: 6V to 40V
Up to 750mA output current
High efficiency (up to 95% )
1200：1 dimming ratio
Typical 5% output current accuracy
Single pin on/off and brightness control using DC
voltage or PWM
Up to 1MHz switching frequency
Inherent open-circuit LED protection
Thermal shutdown to protect IC itself
Temperature compensation to protect LEDs
APPLICATIONS
Low voltage halogen replacement LEDs
Automotive lighting
Low voltage industrial lighting
LED back-up lighting
Illuminated signs
http://www.DataSheet4U.net/
APPLICATION CIRCUIT
IS31LT3352
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
datasheet pdf - http://www.DataSheet4U.net/
1 page  
IS31LT3352
ABSOLUTE MAXIMUM RATINGS (NOTE 1)
Symbol
Parameter
VIN Input voltage
VISENSE
ISENSE voltage
VLX
VADJ ,VADJO,
Rth, RNTC
ILX
Ptot
TOP
TST
Tj MAX
RθJA
LX output voltage
Pin input voltage
Switch output current
Power dissipation
Operating temperature
Storage temperature
Junction temperature
Junction to ambient
ESD Susceptibility(human body
mode)
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
800mA
1.2W
-40 to 85°C
-55 to 150°C
150°C
80°C/W
2kV
ELECTRICAL CHARACTERISTICS
(VIN=12V, Tamb=25°C unless otherwise stated) (NOTE 2)
Symbol
Parameter
Conditions
VIN
IINQoff
IINQon
VISENSE
VSENSEHYS
ISENSE
Input voltage
Quiescent supply current with
output off
Quiescent supply current with
output switching
Mean current sense threshold
voltage
Sense threshold hysteresis
ISENSE pin input current
http://www.DataSheet4U.net/
ADJI pin grounded
ADJI pin floating
Measured on ISENSE
pin with respect to
VIN ADJI pin
floating
IS31LT3352-V1
IS31LT3352-V2
VSENSE =0.1V
VREF
VADJI
VADJIoff
VADJIon
VOS
Internal reference voltage
External control voltage range
on ADJI pin for dc brightness
control
DC voltage on ADJI pin to
switch chip from active (on)
state to quiescent (off) state
DC voltage on ADJI pin to
switch chip from quiescent
(off) state to active (on) state
RTH and RNTC pin offset
voltage
Measured on ADJI pin with pin floating
VADJI falling
VADJI rising
Min.
6
40
Typ.
60
Max.
40
80
450 600
91 95 101
99 105 110
±15
8 10
1.2
Unit
V
μA
μA
mV
%
μA
V
0.3 1.2 V
0.15 0.2 0.25
V
0.2 0.25 0.3
10
V
mV
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 09/01/2011
5
datasheet pdf - http://www.DataSheet4U.net/
5 Page 
IS31LT3352
Vin Rs
LED
CLED
L1
D1
VIN
ISENSE
LX
IS31LT3352
A value of 1μF will reduce nominal ripple current by a
factor three (approx.). Proportionally lower ripple can be
achieved with higher capacitor values. Note that the
capacitor will not affect operating frequency or efficiency,
but it will increase start-up delay, by reducing the rate of
rise of LED voltage.
Operation at low supply voltage
The internal regulator disables the drive to the switch until
the supply has risen above the startup threshold set
internally which makes power MOSFET on-resistance
small enough. Above this threshold, the chip will start to
operate. However, with the supply voltage below the
specified minimum value, the switch duty cycle will be
high and the chip power dissipation will be at a maximum.
Care should be taken to avoid operating the chip under
such conditions in the application, in order to minimize
the risk of exceeding the maximum allowed die
temperature. (See next section on thermal
considerations).
Note that when driving loads of two or more LEDs, the
forward drop will normally be sufficient to prevent the chip
from switching below approximately 6V. This will
minimize the risk of damage to the chip.
Thermal considerations
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. Note that the chip power dissipation will most often
be a maximum at minimum supply voltage. It will also
increase if the efficiency of the circuit is low. This may
result from the use of unsuitable coils, or excessive
parasitic output capacitance on the switch output.
Temperature compensation of output current
High luminance LEDs often need to be supplied with a
temperature compensated current in order to maintain
stable and reliable operation at all drive levels. The LEDs
are usually mounted remotely from the chip. For this
reason, the temperature coefficients of the internal
circuits for the IS31LT3352 have been optimized to
minimize the change in output current when no
compensation is employed. If output current
compensation is required, it is possible to use an external
temperature sensing network - normally using Negative
Temperature Coefficient (NTC) thermistors and/or
diodes, mounted very close to the LED(s). The output of
the sensing network can reduce output current with
increasing temperature through internal circuit.
As shown in the figure below, the temperature
compensation curve is decided by R1, NTC thermistor
R2 and resistor R3. When LED(s) temperature increases,
thermistance of R2 starts to reduce. As R2 reduces to the
point that R2’s thermistance plus R3 resistance equaling
to R1 resistance, temperature compensation function
starts to work and Iout starts to reduce.
The Iout current with temperature compensation’s
equation is:
In the case that 0.3< VADJI <1.2V:
IOUTdc = 0.083*VADJI(R2+R3)/R1*RS
In the case that VADJI >1.2V:
IOUTdc = 0.1*(R2+R3)/R1*RS
R2 and R3 decide the temperature compensation slope,
if R3 is just 0ohm, slope is only decided by thermistor
R2’s parameter B-constant. And larger R3’s resistance
results in slope more even.http://www.DataSheet4U.net/
If the temperature compensation threshold is selected,
larger R2 and R3 selected need larger R1 to match and
vice versa. Too large R1 make Rth pin more sensitive to
noise, too small R1 will make IC current consumption
larger. From 1K to 100K of R1 is recommended.
R3
R2(NTC )
RNTC
ADJO
IS31LT3352
RTH GND
R1
An IS31LT3352 calculator is available from the ISSI to
assist with temperature compensation design and here
are some detail examples as below:
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 09/01/2011
11
datasheet pdf - http://www.DataSheet4U.net/
11 Page | ||
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| PDF Descargar | [ Datasheet IS31LT3352.PDF ] | |
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