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參數(shù)資料
| 型號： | LM3875DWF |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 56 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC |
| 封裝： | WAFER |
| 文件頁數(shù)： | 7/23頁 |
| 文件大小： | 600K |
| 代理商： | LM3875DWF |
Application Information (Continued)
decrease in feedback thus not allowing the amplifier to re-
spond as quickly to nonlinearities. This decreased ability to
respond to nonlinearities increases the THD + N specifica-
tion.
The desired input impedance is set by R
IN. Very high values
can cause board layout problems and DC offsets at the out-
put. The value for the feedback resistance, R
f1, should be
chosen to be a relatively large value (10 k
–100 k), and
the other feedback resistance, Ri, is calculated using stan-
dard op amp configuration gain equations. Most audio ampli-
fiers are designed from the non-inverting amplifier configura-
tion.
DESIGN A 40W/8
AUDIO AMPLIFIER
Given:
Power Output
40W
Load Impedance
8
Input Level
1V
(max)
Input Impedance
100 k
Bandwidth
20 Hz–20 kHz ±0.25 dB
Equations (5), (6) give:
40W/8
V
opeak = 25.3V
I
opeak = 3.16A
Therefore the supply required is: ±30.3V @3.16A
With 15% regulation and high line the final supply voltage is
±38.3V using Equation (7). At this point it is a good idea to
check the Power Output vs Supply Voltage to ensure that the
required output power is obtainable from the device while
maintaining low THD + N. It is also good to check the Power
Dissipation vs Supply Voltage to ensure that the device can
handle the internal power dissipation. At the same time de-
signing in a relatively practical sized heat sink with a low
thermal resistance is also important. Refer to Typical Per-
formance Characteristics graphs and the Thermal Con-
siderations section for more information.
The minimum gain from
Equation (8) is: A
V ≥ 18
We select a gain of 21 (Non-Inverting Amplifier); resulting in
a sensitivity of 894 mV.
Letting R
IN equal 100 k gives the required input imped-
ance, however, this would eliminate the “volume control” un-
less an additional input impedance was placed in series with
the 10 k
potentiometer that is depicted in Figure 1. Adding
the additional 100 k
resistor would ensure the minimum re-
quired input impedance.
For low DC offsets at the output we let R
f1 = 100 k. Solving
for Ri (Non-Inverting Amplifier) gives the following:
Ri = R
f1/(AV 1) = 100k/(21 1) = 5k; use 5.1 k
The bandwidth requirement must be stated as a pole, i.e.,
the 3 dB frequency. Five times away from a pole give
0.17 dB down, which is better than the required 0.25 dB.
Therefore:
f
L = 20 Hz/5 = 4Hz
f
H = 20 kHz x 5 = 100 kHz
At this point, it is a good idea to ensure that the Gain Band-
width Product for the part will provide the designed gain out
to the upper 3 dB point of 100 kHz. This is why the minimum
GBWP of the LM3875 is important.
GBWP = A
V xf3dB = 21 x 100 kHz = 2.1 MHz
GBWP = 2.0 MHz (min) for LM3875
Solving for the low frequency roll-off capacitor, Ci, we have:
Ci > 1/(2
π Ri f
L) = 7.8 F; use 10 F.
Definition of Terms
Input Offset Voltage: The absolute value of the voltage
which must be applied between the input terminals through
two equal resistances to obtain zero output voltage and cur-
rent.
Input Bias Current: The absolute value of the average of
the two input currents with the output voltage and current at
zero.
Input Offset Current: The absolute value of the difference
in the two input currents with the output voltage and current
at zero.
Input Common-Mode Voltage Range (or Input Voltage
Range): The range of voltages on the input terminals for
which the amplifier is operational. Note that the specifica-
tions are not guaranteed over the full common-mode voltage
range unless specifically stated.
Common-Mode
Rejection:
The
ratio
of
the
input
common-mode voltage range to the peak-to-peak change in
input offset voltage over this range.
Power Supply Rejection: The ratio of the change in input
offset voltage to the change in power supply voltages pro-
ducing it.
Quiescent Supply Current: The current required from the
power supply to operate the amplifier with no load and the
output voltage and current at zero.
Slew Rate: The internally limited rate of change in output
voltage with a large amplitude step function applied to the in-
put.
Class B Amplifier: The most common type of audio power
amplifier that consists of two output devices each of which
conducts for 180 of the input cycle. The LM3875 is a
Quasi-AB type amplifier.
Crossover Distortion: Distortion caused in the output stage
of a class B amplifier. It can result from inadequate bias cur-
rent providing a dead zone where the output does not re-
spond to the input as the input cycle goes through its zero
crossing point. Also for ICs an inadequate frequency re-
sponse of the output PNP device can cause a turn-on delay
giving crossover distortion on the negative going transistion
through zero crossing at the higher audio frequencies.
THD+N: Total Harmonic Distortion plus Noise refers to the
measurement technique in which the fundamental compo-
nent is removed by a bandreject (notch) filter and all remain-
ing energy is measured including harmonics and noise.
Signal-to-Noise Ratio: The ratio of a system’s output signal
level to the system’s output noise level obtained in the ab-
sence of a signal. The output reference signal is either speci-
fied or measured at a specified distortion level.
Continuous Average Output Power: The minimum sine
wave continuous average power output in watts (or dBW)
that can be delivered into the rated load, over the rated
bandwidth, at the rated maximum total harmonic distortion.
Music Power: A measurement of the peak output power ca-
pability of an amplifier with either a signal duration suffi-
ciently short that the amplifier power supply does not sag
during the measurement, or when high quality external
power supplies are used. This measurement (an IHF stan-
dard) assumes that with normal music program material the
amplifier power supplies will sag insignificantly.
www.national.com
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3875T | 功能描述:IC AMP AUDIO PWR 56W AB TO220-11 RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Overture™ 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機(jī)，2-通道（立體聲） 在某負(fù)載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風(fēng)，靜音，短路保護(hù)，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM3875T | 制造商:Texas Instruments 功能描述:IC AMP AUDIO 100W 3875 SIL-11 |
| LM3875T/NOPB | 制造商:Texas Instruments 功能描述:Audio Amp Speaker 1-CH Mono 56W Class-AB 11-Pin(11+Tab) TO-220 |
| LM3875TF | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM3875TF/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
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