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PDF IS31LT3353 Data sheet ( Hoja de datos )
| Número de pieza | IS31LT3353 | |
| Descripción | 40V/1A BUCK LED DRIVER | |
| Fabricantes | ISSI | |
| Logotipo |  |
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IS31LT3353
40V/1A BUCK LED DRIVER WITH INTERNAL SWITCH
October 2014
GENERAL DESCRIPTION
The IS31LT3353 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 LED voltage.
The chip operates from an input supply between 6V
and 40V and provides an externally adjustable output
current of up to 1A.
The IS31LT3353 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 output current can be dynamically adjusted by
adding either a digital PWM or analog voltage level
signal to the ADJ pin. A PWM signal will provide a
gated output current while a voltage signal will
generate a continuously linear output current.
Applying a voltage less than 0.2V to the ADJ pin
turns the output off and switches the chip into a low
current standby state.
The chip is assembled in SOT23-5 package. It
operates from 6V to 40V over the temperature range
of -40°C to +125°C.
FEATURES
Up to 1A output current
High efficiency (up to 97% )
Wide input voltage range: 6V to 40V
Internal 40V power switch
Simple low parts count
Typical 3% output current accuracy
Single pin on/off and brightness control using
DC voltage or PWM
Up to 1MHz switching frequency
Inherent LED open-circuit/short-circuit
protection
Thermal shutdown protection circuitry
Up to 1200: 1 dimming rate
APPLICATIONS
LED MR16, MR11 spot light
LED street light
PAR light
Industrial lighting
Refrigeration lights
Other LED lighting
APPLICATION CIRCUIT
Figure 1 Typical Application Circuit
Note: The capacitor, C2, can’t be removed. And it should be placed as close as possible to the VIN and GND pins, otherwise the operation
might be abnormal.
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 10/13/2014
1
1 page  
IS31LT3353
ELECTRICAL CHARACTERISTICS (CONTINUED)
Test conditions: VIN = 12V, TA =TJ = 25°C, unless otherwise stated. (Note 3)
Symbol
Parameter
Conditions
Min. Typ. Max. Unit
ILX_LEAK
RLX
tON_MIN
tOFF_MIN
DDIM
LX switch leakage current
LX switch ‘ON’ resistance
Minimum switch ‘ON’ time
Minimum switch ‘OFF’ time
Typical contrast ratio
LX switch ‘ON’ (Note 4)
LX switch ‘OFF’ (Note 4)
fPWM =100Hz, VIN =15V,
1LED, L=27µH
0.5
200
200
1200:1
1
1
μA
Ω
ns
ns
1
fLX_MAX
Recommended maximum
operating frequency
1 MHz
DLX
Recommended duty cycle range
of output switch at fLX_MAX
TPD
Internal comparator propagation
delay
(Note 4)
30 70 90 %
50 ns
TSD Thermal shutdown temperature
TSD_HYS Thermal shutdown hysteresis
(Note 4)
(Note 4)
150 °C
20 °C
Note 3: Production testing of the device is performed at 25°C. Functional operation of the device and parameters specified over -40°C to
+125°C temperature range, are guaranteed by design, characterization and process control.
Note 4: Guaranteed by design.
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 10/13/2014
5
5 Page 
IS31LT3353
overall efficiency. This capacitor has to supply the
relatively high peak current to the coil and smooth the
current ripple on the input supply.
If the source is DC supply, the capacitor is decided
by ripple of the source, the value is given by Equation
(3):
CMIN
I F tON
U MAX
(3)
IF is the value of output current, U MAX is the ripple
of power supply. tON is the “ON” time of MOSFET.
The value is higher than the minimum value. A
100µF capacitor is recommended.
If the source is an AC supply, typical output voltages
ripple from a nominal 12V AC transformer can be
±10%.If the input capacitor value is lower than 220μF,
the AC input waveform is distorted, sometimes the
lowest value will be lower than the forward voltage of
LED strings. This lower the average current of the
LEDs. So it is recommended to set the value of the
capacitor bigger than 220µF.
To minimize the ground bounce, It must connect a
0.1µF capacitor as close to device as possible. This
capacitor can’t be removed, otherwise the operation
might be abnormal.
INDUCTOR SELECTION
Recommended inductor values for the IS31LT3353
are in the range 47μH to 220μH.
Higher values of inductance are recommended at
higher supply voltages and low output current in
order to minimize errors due to switching delays,
which result in increased ripple and lower efficiency.
Higher values of inductance also result in a smaller
change in output current over the supply voltage
range. The inductor should be mounted as close to
the chip as possible with low resistance connections
to the LX and VIN pins.
The chosen coil should have a saturation current
higher than the peak output current and a continuous
current rating above the required mean output
current. It is recommended to use inductor with
saturation current bigger than 1.5A for 1A output
current and inductor with saturation current bigger
than 500mA for 350mA output current.
The inductor value should be chosen to maintain
operating duty cycle and switch 'on/off' times within
the specified limits over the supply voltage and load
current range.
The following equations can be used as a guide.
LX Switch 'ON' time:
Integrated Silicon Solution, Inc. – www.issi.com
Rev. A, 10/13/2014
tON
VIN
VLED
L I
I AVG (RS
RL
RLX )
Note: tON_MIN > 200ns.
LX Switch 'OFF' time:
(4)
tOFF
VLED
VD
L I
I AVG (RL
RS )
(5)
Note: tOFF_MIN > 200ns.
Where:
L is the coil inductance (H)
RL is the coil resistance (Ω)
IAVG is the required LED current (A)
∆I is the coil peak-peak ripple current (A) {Internally
set to 0.3 × IAVG}
VIN is the supply voltage (V)
VLED is the total LED forward voltage (V)
RLX is the switch resistance (Ω)
VD is the diode forward voltage at the required load
current (V)
Example:
For VIN=12V, L=47μH, RL=0.26Ω, VLED=3.4V, IAVG
=333mA, VD =0.36V, RS = 0.3Ω, RLX=0.5Ω:
tON
12
3.4
47 0.3
0.333
0.333
(0.3 0.26
0.5)
0.569s
tOFF
47 0.3 0.333
3.4 0.36 0.333 (0.26 0.3)
1.19s
This gives an operating frequency of 569kHz and a
duty cycle of 32%.
Optimum performance will be achieved by setting the
duty cycle close to 50% at the nominal supply voltage.
This helps to equalize the undershoot and overshoot
and improves temperature stability of the output
current.
DIODE SELECTION
For maximum efficiency and performance, the
rectifier (D1) should be a fast low capacitance
Schottky diode with low reverse leakage at the
maximum operating voltage and temperature.
If alternative diodes are used, it is important to select
parts with a peak current rating above the peak coil
current and a continuous current rating higher than
the maximum output load current. It is very important
to consider the reverse leakage of the diode when
operating at high temperature. Excess leakage will
increase the power dissipation in the device.
The higher forward voltage and overshoot due to
11
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| PDF Descargar | [ Datasheet IS31LT3353.PDF ] | |
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