LT1786FCS Linear Technology, LT1786FCS Datasheet - Page 17

• Manufacturer Part Number: LT1786FCS
• Description: IC SW REG CCFL SMBUS PROG 16SOIC
• Manufacturer: Linear Technology

Specifications of LT1786FCS

• Applications: Converter, CCFL
• Voltage - Input: 4.5 ~ 30 V
• Number Of Outputs: 1
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Voltage - Output: -

APPLICATIONS
the use of an aluminum electrolytic for the transformer
center-tap bypass capacitor with an ESR greater than or
equal to 0.5 . This lowers the peak surge currents to an
acceptable level. In general, the wire and trace inductance
in this path also help reduce the di/dt of the surge current.
This issue only exists with floating lamp circuits as
grounded lamp circuits do not make use of the high-side
sense resistor.
Input Capacitor Type
Caution must be used in selecting the input capacitor type
for switching regulators. Aluminum electrolytics are elec-
trically rugged and the lowest cost, but are physically large
to meet required ripple current ratings, and size con-
straints (especially height) may preclude their use. Ce-
ramic capacitors are now available in larger values and
their high ripple current and voltage rating make them
ideal for input bypassing.
Solid tantalum capacitors would be a good choice except
for a history of occasional failure when subjected to large
current surges during start-up. The input bypass capaci-
tor of regulators can see these high surges when a battery
or high capacitance source is connected. Some manufac-
turers have developed tantalum capacitor lines specially
tested for surge capability (AVX TPS series for instance),
but even these units may fail if the input voltage surge
approaches the capacitor’s maximum voltage rating. AVX
recommends derating the capacitor voltage by 2:1 for high
surge applications.
Applications Support
Linear Technology invests an enormous amount of time,
resources and technical expertise in understanding,
designing and evaluating backlight/LCD contrast solu-
tions for system designers. The design of an efficient and
U
INFORMATION
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compact LCD backlight system is a study of compromise
in a transduced electronic system. Every aspect of the
design is interrelated and any design change requires
complete re-evaluation for all other critical design param-
eters. Linear Technology has engineered one of the most
complete test and evaluation setups for backlight designs
and understands the issues and tradeoffs in achieving a
compact, efficient and economical customer solution.
Linear Technology welcomes the opportunity to discuss,
design, evaluate and optimize any backlight/LCD contrast
system with a customer. For further information on back-
light/LCD contrast designs, consult the References.
References
1. Williams, Jim. August 1992. Illumination Circuitry for
Liquid Crystal Displays . Linear Technology Corporation,
Application Note 49.
2. Williams, Jim. August 1993. Techniques for 92% Effi-
cient LCD Illumination . Linear Technology Corporation,
Application Note 55.
3. Bonte, Anthony. March 1995. LT1182 Floating CCFL
with Dual Polarity Contrast . Linear Technology Corpora-
tion, Design Note 99.
4. Williams, Jim. April 1995. A Precision Wideband Cur-
rent Probe for LCD Backlight Measurement . Linear Tech-
nology Corporation, Design Note 101.
5. LT1182/LT1183/LT1184/LT1184F Data Sheet. CCFL/
LCD Contrast Switching Regulators . April 1995. Linear
Technology Corporation.
6. Williams, Jim. November 1995. A Fourth Generation of
LCD Backlight Technology . Linear Technology Corpora-
tion, Application Note 65.
LT1786F
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