參數(shù)資料
型號(hào)： LM4891M/NOPB
廠商： National Semiconductor
文件頁(yè)數(shù)： 6/21頁(yè)
文件大小： 0K
描述： IC AMP AUDIO PWR 1W MONO 8SOIC
標(biāo)準(zhǔn)包裝： 95
系列： Boomer®
類型： AB 類
輸出類型： 1-通道（單聲道）
在某負(fù)載時(shí)最大輸出功率 x 通道數(shù)量： 1W x 1 @ 8 歐姆
電源電壓： 2.2 V ~ 5.5 V
特點(diǎn)： 消除爆音，關(guān)機(jī)，熱保護(hù)
安裝類型： 表面貼裝
供應(yīng)商設(shè)備封裝： 8-SOIC
封裝/外殼： 8-SOIC（0.154"，3.90mm 寬）
包裝： 管件
配用： LM4891MBD-ND - BOARD EVALUATION LM4891M
其它名稱： *LM4891M
LM4891M
OBSOLETE
SNAS122E – MAY 2001 – REVISED APRIL 2013
AUDIO POWER AMPLIFIER DESIGN
A 1W/8
AUDIO AMPLIFIER
Given:
Power Output
1 Wrms
Load Impedance
8
Input Level
1 Vrms
Input Impedance
20 k
Bandwidth
100 Hz–20 kHz ± 0.25 dB
A designer must first determine the minimum supply rail to obtain the specified output power. By extrapolating
from the Output Power vs Supply Voltage graphs in the TYPICAL PERFORMANCE CHARACTERISTICS
section, the supply rail can be easily found. A second way to determine the minimum supply rail is to calculate
the required Vopeak using Equation 2 and add the output voltage. Using this method, the minimum supply voltage
would be (Vopeak + (VODTOP + VODBOT)), where VODBOT and VODTOP are extrapolated from the Dropout Voltage vs
Supply Voltage curve in the TYPICAL PERFORMANCE CHARACTERISTICS section.
(2)
5V is a standard voltage, in most applications, chosen for the supply rail. Extra supply voltage creates headroom
that allows the LM4891 to reproduce peaks in excess of 1W without producing audible distortion. At this time, the
designer must make sure that the power supply choice along with the output impedance does not violate the
conditions explained in the POWER DISSIPATION section.
Once the power dissipation equations have been addressed, the required differential gain can be determined
(3)
AVD = (Rf/Ri) 2
From Equation 3, the minimum AVD is 2.83; use AVD = 3.
Since the desired input impedance was 20 k
, and with a AVD of 3, a ratio of 1.5:1 of Rf to Ri results in an
allocation of Ri = 20 k and Rf = 30 k. The final design step is to address the bandwidth requirements which
must be stated as a pair of
3 dB frequency points. Five times away from a 3 dB point is 0.17 dB down from
passband response which is better than the required ±0.25 dB specified.
fL = 100 Hz/5 = 20 Hz
fH = 20 kHz * 5 = 100 kHz
As stated in the EXTERNAL COMPONENTS DESCRIPTION section, Ri in conjunction with Ci create a highpass
filter.
Ci ≥ 1/(2π*20 k*20 Hz) = 0.397 F; use 0.39 F
The high frequency pole is determined by the product of the desired frequency pole, fH, and the differential gain,
AVD. With a AVD = 3 and fH = 100 kHz, the resulting GBWP = 300 kHz which is much smaller than the LM4891
GBWP of 2.5 MHz. This figure displays that if a designer has a need to design an amplifier with a higher
differential gain, the LM4891 can still be used without running into bandwidth limitations.
14
Copyright 2001–2013, Texas Instruments Incorporated
Product Folder Links: LM4891
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