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PDF LT3517 Data sheet ( Hoja de datos )
| Número de pieza | LT3517 | |
| Descripción | Full-Featured LED Driver | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LT3517
Full-Featured LED Driver
with 1.5A Switch Current
FEATURES
DESCRIPTION
■ 5000:1 True Color PWMTM Dimming Ratio
■ 1.5A, 45V Internal Switch
■ 100mV High Side Current Sense
■ Open LED Protection
■ Adjustable Frequency: 250kHz to 2.5MHz
■ Wide Input Voltage Range:
Operation from 3V to 30V
Transient Protection to 40V
■ Operates in Boost, Buck Mode and Buck-Boost Mode
■ Gate Driver for PMOS LED Disconnect*
■ Constant-Current and Constant-Voltage Regulation
■ CTRL Pin Provides 10:1 Analog Dimming
■ Low Shutdown Current: <1μA
■ Available in (4mm × 4mm) 16-Lead QFN and 16-Pin
TSSOP Packages
APPLICATIONS
■ Display Backlighting
■ Automotive and Avionic Lighting
■ Illumination
■ Scanners
The LT®3517 is a current mode DC/DC converter with an
internal 1.5A, 45V switch specifically designed to drive
LEDs. The LT3517 operates as a LED driver in boost,
buck mode and buck-boost mode. It combines a tradi-
tional voltage loop and a unique current loop to operate
as a constant-current source or constant-voltage source.
Programmable switching frequency allows optimization of
the external components for efficiency or component size.
The switching frequency of LT3517 can be synchronized
to an external clock signal. The LED current is externally
programmable with a 100mV sense resistor. The external
PWM input provides up to 5000:1 LED dimming. The CTRL
pin provides further 10:1 dimming ratio.
The LT3517 is available in the tiny footprint 16-Lead QFN
(4mm × 4mm) and the16-Pin TSSOP packages. The LT3517
provides a complete solution for both constant-voltage
and constant-current applications.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
True Color PWM is a trademark of Linear Technology Corporation. Patent Pending.
All other trademarks are the property of their respective owners.
*Patents Pending.
TYPICAL APPLICATION
1A Buck Mode LED Driver
PVIN
24V
VIN
3.3V
2.2μF
VREF
PWM
2.2μF
100mΩ
ISP
VIN
SHDN
ISN TG
SW
LT3517
CTRL
FB
PWM
SS
SYNC
RT
TGEN VREF VC GND
0.1μF
1A
16.9k
1MHz
10μF
15μH
0.1μF
3517 TA01a
Efficiency
100
CTRL = VREF
90
80
70
60
50
40
0
20 40 60 80
PWM DUTY CYCLE (%)
100
3517 TA01b
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TYPICAL PERFORMANCE CHARACTERISTICS
LT3517
VISP – VISN Threshold vs
Temperature
104
VIN = 5V
103 VISP = 24V
VC = 1V
102 VCTRL = 2V
101
100
99
98
97
96
–40 –20 0 20 40 60 80 100 120 140 160
TEMPERATURE (°C)
3517 G04
VISP – VISN Threshold vs VISP
105
VCTRL = 2V
104 VIN = 5V
103
TA = 25°C
VC = 1V
102
101
100
99
98
97
96
95
0
10 20 30 40 50
VISP (V)
3517 G07
Switch Current Limit vs
Temperature
2.5
VIN = 5V
2.0
1.5
1.0
0.5
0
–40 –20 0 20 40 60 80 100 120 140 160
TEMPERATURE (°C)
3518 G05
Reference Voltage vs
Temperature
2.02
VIN = 5V
2.01
2.00
1.99
1.98
–40 –20 0 20 40 60 80 100 120 140 160
TEMPERATURE (°C)
3517 G08
Oscillator Frequency vs
Temperature
2.5
VIN = 5V
RT = 6.04k
2.3
2.1
1.9
1.7
1.5
–40 –20 0 20 40 60 80 100 120 140 160
TEMPERATURE (°C)
3517 G06
Quiescent Current vs VIN
8
TA = 25°C
7 VC = 0V
6
5
4
3
2
1
0
0 10 20 30
VIN (V)
40
3517 G09
FB Pin Threshold vs Temperature
1.04
VIN = 5V
1.03
1.02
1.01
1.00
0.99
PMOS Turn-On
5V
PWM
0V
40V
TG
30V
0.98
–40 –20 0 20 40 60 80 100 120 140 160
TEMPERATURE (°C)
3517 G10
VISP = 40V
200ns/DIV
PMOS Turn-Off
5V
PWM
0V
40V
TG
30V
3517 G11
VISP = 40V
200ns/DIV
3517 G11
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LT3517
APPLICATIONS INFORMATION
performance, size and cost. The compensation resistor
and capacitor at VC are selected to optimize control loop
stability. For typical LED applications, a 10nF compensa-
tion capacitor at VC is adequate and a series resistor is not
required. A compensation resistor may be used to increase
the slew rate on the VC pin to maintain tighter regulation
of LED current during fast transients on VIN or CTRL.
Diode Selection
The Schottky diode conducts current during the interval
when the switch is turned off. Select a diode rated for
the maximum SW voltage. If using the PWM feature for
dimming, it is important to consider diode leakage, which
increases with the temperature, from the output during the
PWM low interval. Therefore, choose the Schottky diode
with sufficiently low leakage current. Table 3 has some
recommended component vendors.
Table 3. Schottky Diodes
PART NUMBER
Diodes Inc.
DFLS160
Zetex
ZLLS1000TA
International Rectifier
10MQ060N
VR (V)
60
40
60
IAVE (A)
1
1
1.5
Board Layout
The high speed operation of the LT3517 demands careful
attention to board layout and component placement. The
Exposed Pad of the package is the only GND terminal of
the IC and is also important for thermal management of
the IC. It is crucial to achieve a good electrical and thermal
contact between the Exposed Pad and the ground plane of
the board. To reduce electromagnetic interference (EMI),
it is important to minimize the area of the SW node. Use
a GND plane under SW and minimize the length of traces
in the high frequency switching path between SW and
GND through the diode and the capacitors. Since there is
a small DC input bias current to the ISN and ISP inputs,
resistance in series with these inputs should be minimized
and matched, otherwise there will be an offset. Finally, the
bypass capacitor on the VIN supply to the LT3517 should
be placed as close as possible to the VIN terminal of the
device.
Soft-Start
For many applications, it is necessary to minimize the
inrush current at start-up. The built-in soft-start circuit
significantly reduces the start-up current spike and
output voltage overshoot. A typical value for the soft-start
capacitor is 0.1μF.
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| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LT3517.PDF ] | |
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