LT3950
60V, 1.5A LED Driver with Internal
Exponential Scale Dimming
FEATURES
DESCRIPTION
The LT®3950 is a multitopology DC/DC converter designed
specifically to drive high current LEDs. It contains a 1.5A,
60V DMOS switch and supports an external PWM dim-
ming PMOS. The LT3950 has an internal PWM generator
for dimming that maps an analog control signal to an
exponential scale used to define PWM dimming duty ratio.
Using an exponential scale to define duty ratio preserves
dimming resolution across a wide range of LED current.
In addition to operating as a constant current source, the
LT3950 also provides output voltage regulation. This can
be used to prevent damage to the part in case of open LED
events. A programmable switching frequency offers flex-
ibility in design for higher efficiency or reduced compo-
nent size. Enabling spread spectrum frequency modula-
tion reduces EMI. The switching frequency can also easily
be synchronized by driving the SYNC/SPRD pin with an
external clock. LED current is programmed with a single
external sense resistor and can be adjusted from zero to
full-scale by an analog signal at the CTRL pin.
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Operates in Boost, SEPIC, Buck Mode and Buck-
Boost Mode
128:1 Internal Exponential Scale PWM Dimming
Wide Input Voltage Range (3V to 60V)
1.5A, 60V Internal Switch
20000:1 External PWM Dimming at 100Hz
2% LED Current and Output Voltage Regulation
PMOS Switch Driver for PWM Dimming
LED Short/Open Protection and Indication
Constant Voltage and Constant Current Regulation
Adjustable 300kHz to 2MHz Switching Frequency
Adjustable 100Hz to 1kHz PWM Generator Frequency
Internal Spread Spectrum Frequency Modulation
Easy Synchronization to External Clock
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Programmable V UVLO with Hysteresis
Available in 16-Lead MSOP Package
IN
APPLICATIONS
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Display Backlighting
Automotive and Avionic Lighting
All registered trademarks and trademarks are the property of their respective owners. Protected
by U.S. Patents, including 7199560, 7321203, 7746300, 8116045. Patents pending.
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TYPICAL APPLICATION
10W LED Driver for Automotive, 2MHz, 90% Efficient
Efficiency and Power Loss with
and without PWM Dimming
V
10µH
1Ω
IN
3V TO16V DC
TRANSIENT
TO 48V
ꢀ00
ꢀꢁ
ꢀꢁ
ꢀꢀ
ꢀꢁ
ꢀ0
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀꢁ
ꢀ0
ꢀ.000
ꢀ.ꢁꢂ0
ꢀ.ꢁ00
ꢀ.ꢀꢁ0
ꢀ.000
ꢀ.ꢁꢂ0
ꢀ.ꢁ00
ꢀ.ꢁꢂ0
ꢀ.000
0.ꢀꢁ0
0.ꢀ00
2.2µF
2.2µF
V
SW
ISP
ISN
ꢀꢁꢁꢂꢃꢂꢀꢄꢃꢅ ꢆ00ꢇ ꢈꢄ
IN
EN/UVLO
1M
100k
ꢀꢁꢁꢂꢃꢂꢀꢄꢃꢅ ꢆꢀꢁꢁ.ꢇ ꢈꢉ
ꢊ0ꢋ ꢌꢍꢎ ꢏꢂꢎꢎꢂꢄꢐ
FAULT
FAULT
FB
10W
LED
INTV
CC
24.9k
LT3950
POWER
(DERATED
BELOW
ꢀ
ꢀ0ꢁ ꢂꢃꢄ ꢅꢆꢄꢄꢆꢇꢈ
ꢀꢁꢂꢂꢃ ꢄꢅꢅ.
1µF
CTRL
PWMTG
VC
V
= 7V)
IN
267k
ꢀ
ꢀ00ꢁ ꢂꢃ
ꢀꢁꢂꢂ
PWM
39k
220pF
SYNC/SPRD RP
RT
GND
100k
300Hz
182k
2MHz
45.3k
ꢀ0 ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢀ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀꢁ ꢀ0
ꢀꢁꢂ
ꢀ
ꢀꢁ
3950 TA01a
ꢀꢁꢂ0 ꢃꢄ0ꢅꢆ
Rev. 0
1
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