Datasheet

LTC4081
22
4081f
There are several types of ceramic capacitors with consider-
ably different characteristics. Y5V ceramic capacitors have
apparently higher packing density but poor performance
over their rated voltage or temperature ranges. Under
given voltage and temperature conditions, X5R and X7R
ceramic capacitors should be compared directly by case
size rather than specifi ed value for a desired minimum
capacitance. Some manufacturers provide excellent data on
their websites about achievable capacitance. Table 2 shows
a list of several ceramic capacitor manufacturers.
Table 2. Recommended Ceramic Capacitor Manufacturers
Taiyo Yuden www.t-yuden.com
AVX www.avxcorp.com
Murata www.murata.com
TDK www.tdk.com
Board Layout Considerations
To be able to deliver maximum charge current under all
conditions, it is critical that the exposed metal pad on the
backside of the LTC4081’s package has a good thermal
contact to the PC board ground. Correctly soldered to a
2500mm
2
double-sided 1 oz. copper board, the LTC4081
has a thermal resistance of approximately 43°C/W. Failure
to make thermal contact between the exposed pad on the
backside of the package and the copper board will result
in thermal resistance far greater than 43°C/W.
Furthermore due to its high frequency switching circuitry,
it is imperative that the input capacitor, BAT pin capaci-
tor, inductor, and the output capacitor be as close to the
LTC4081 as possible and that there is an unbroken ground
plane under the LTC4081 and all of its high frequency
components.
APPLICATIO S I FOR ATIO
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