L3380 データシートの表示（PDF） - Unisonic Technologies
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L3380 Datasheet PDF : 9 Pages
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L3380
EXTERNAL COMPONENTS(Cont.)
CMOS IC
Since the pulse current flows through the transistor, the exact Rb value should be finely tuned by the
experiment. Generally, a small Rb value can increase the output current capability, but the efficiency will
decrease due to more energy is used to drive the transistor.
Moreover, a speed up capacitor, C2, should be connected in parallel with R1 to reduce switching loss and
improve efficiency. C2 can be calculated by the equation below:
C2 ≤
1
2π × R1× fOSC × 0.7
It is due to the variation in the characteristics of the transistor used. The calculated value should be used as
the initial test value and the optimized value should be obtained by the experiment.
*Enhancement MOS FET
For enhancement N-channel MOSFET, since enhancement MOSFET is a voltage driven, it is a more efficient
switch than a BJT transistor. However, the MOSFET requires a higher voltage to turn on as compared with BJT
transistors. An enhancement N-channel MOSFET can be selected by the following guidelines:
-Input capacitance less than 700pF.
-Low gate threshold voltage.
-Low on-resistance.
-The allowable maximum current of drain should be larger than peak current of inductor.
UTC assumes no responsibility for equipment failures that result from using products at values that
exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or
other parameters) listed in products specifications of any and all UTC products described or contained
herein. UTC products are not designed for use in life support appliances, devices or systems where
malfunction of these products can be reasonably expected to result in personal injury. Reproduction in
whole or in part is prohibited without the prior written consent of the copyright owner. The information
presented in this document does not form part of any quotation or contract, is believed to be accurate
and reliable and may be changed without notice.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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QW-R502-099,A
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