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FDS4953 датащи(PDF) 10 Page - Microsemi Corporation |
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FDS4953 датащи(HTML) 10 Page - Microsemi Corporation |
10 / 18 page LXE1710 EVALUATION BOARD USER GUIDE Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 10 Copyright © 2000 Rev. 1.1, 2000-12-01 evaluation board is a second order, LC type filter as shown below. Tradeoffs between performance and component cost must be considered when determining the complexity or type of filter selected. OUT+ OUT- L 15µH L 15µH C 0.68µF C 0.68µF R Its Laplace Transform function is: ω ω ω ω RC Q LC S Q S C S LC S RC S C S = = + + = + + = 1 Where 1 1 H(S) 2 2 2 The Class-D amplifier evaluation board design has a pass-band of 20Hz to 20kHz to support the audio frequency range and is configured to utilize a switching or oscillator frequency fs = 500kHz. Depending on the application, this oscillator frequency may be adjusted (see section on Oscillator Configuration) to optimize amplifier performance or modified for other considerations such as EMI effects. Further requirements of the filter are that the pass band attenuation of switching frequency fs should be lower than 40dB and the corner frequency of the LC filter should be set higher than 20kHz to avoid attenuating audio signals in the desired audio band by more than 1dB. A speaker DC impedance o '- C = 50kHz corner frequency are defined for the evaluation board. The Q (selectivity factor or ratio of the center frequency divided by the bandwidth) of the filter must also be considered when designing a filter. Too high a Q will result in a boost of the audio signal across the audio band whereas a low Q will cause too much attenuation of the signal. A Q value of 0.707 provides the required audio response and is used in the calculation below. Board Evaluation in the used is µF 68 . 0 µ 56 . 0 ) 50000 )( 2 ( 4 707 . 0 ) f 2 ( = = = = = C F R Q R Q C C π π ω To Compute the Inductor Value: Board Evaluation in the used is µH 15 µ 9 . 14 ) µ 68 (. )] 50000 )( 2 [( 1 ) f 2 ( 1 1 2 2 2 = = = = = L H C C L C π π ω LXE1710 Evaluation Board Frequency Response -15 +15 -12.5 -10 -7.5 -5 -2.5 +0 +2.5 +5 +7.5 +10 +12.5 10 80 k 20 50 10 20 50 1k 2k 5k 10 k 20 k 50 k Frequency (Hz) Frequency response of the audio amplifier was $ " ) ,! - $- + - - "" ' . ! - , ) " + )/ . –4dB attenuation respectively. Therefore, to improve frequency response performance for other loads, the value of Q must be increased/decreased by changing the capacitor. Since a different value C will affect the corner frequency, values for L and C must be recalculated. Below are recommended inductor and capacitor values for 2 , - single stage LC filter design. Capacitor C (µF) Inductor L (µH) 1.0 10 0.68 15 0.47 22 Filter Component Values Please note: These recommended values are guidelines for speaker loads. Actual speakers have varying impedances, which may require revised filter calculations and optimization. Furthermore, your application may have different design goals than those chosen for the LX1710 evaluation board. |
Аналогичный номер детали - FDS4953 |
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Аналогичное описание - FDS4953 |
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