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參數(shù)資料
| 型號： | LM1876TF |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | Overture⑩ Audio Power Amplifier Series Dual 20W Audio Power Amplifier with Mute and Standby Modes |
| 中文描述： | 22 W, 2 CHANNEL, AUDIO AMPLIFIER, PZFM15 |
| 封裝： | ISOLATED, PLASTIC, TO-220, 15 PIN |
| 文件頁數(shù)： | 14/16頁 |
| 文件大小： | 593K |
| 代理商： | LM1876TF |
Application Information
(Continued)
To achieve a transient free power-up and power-down, the
voltage seen at the input terminals should be ideally the
same. Such a signal will be common-mode in nature, and
will be rejected by the LM1876. In Figure 3 the resistor R
serves to keep the inputs at the same potential by limiting the
voltage difference possible between the two nodes. This
should significantly reduce any type of turn-on pop, due to an
uneven charging of the amplifier inputs. This charging is
based on a specific application loading and thus, the system
designer may need to adjust these values for optimal perfor-
mance.
As shown in Figure 3 the resistors labeled R
help bias up
the LM1876 off the half-supply node at the emitter of the
2N3904. But due to the input and output coupling capacitors
in the circuit, along with the negative feedback, there are two
different values of R
, namely 10 k
and 200 k
. These re-
sistors bring up the inputs at the same rate resulting in a pop-
less turn-on.Adjusting these resistors values slightly may re-
duce pops resulting from power supplies that ramp
extremely quick or exhibit overshoot during system turn-on.
AUDIO POWER AMPLlFIER DESIGN
Design a 15W/8
Audio Amplifier
Given:
Power Output
Load Impedance
Input Level
Input Impedance
Bandwidth
15 Wrms
8
1 Vrms(max)
47 k
20 Hz20 kHz
±
0.25 dB
A designer must first determine the power supply require-
ments in terms of both voltage and current needed to obtain
the specified output power. V
can be determined from
equation (4) and I
OPEAK
from equation (5).
(4)
(5)
To determine the maximum supply voltage the following con-
ditions must be considered. Add the dropout voltage to the
peak output swing V
, to get the supply rail at a current
of I
OPEAK
. The regulation of the supply determines the un-
loaded voltage which is usually about 15% higher. The sup-
ply voltage will also rise 10% during high line conditions.
Therefore the maximum supply voltage is obtained from the
following equation.
Max supplies
≈
±
(V
OPEAK
+ V
OD
) (1 + regulation) (1.1)
For 15W of output power into an 8
load, the required
V
is 15.49V. A minimum supply rail of 20.5V results
from adding V
OPEAK
and V
OD
. With regulation, the maximum
supplies are
±
is 1.94A from
equation (5). It should be noted that for a dual 15W amplifier
into an 8
load the I
drawn from the supplies is twice
1.94 Apk or 3.88 Apk. At this point it is a good idea to check
the Power Output vs Supply Voltage to ensure that the re-
quired output power is obtainable from the device while
maintaining low THD+N. In addition, the designer should
verify that with the required power supply voltage and load
impedance, that the required heatsink value
θ
is feasible
given system cost and size constraints. Once the heatsink
issues have been addressed, the required gain can be deter-
mined from Equation (6).
(6)
From equation 6, the minimum A
V
is:
By selecting a gain of 21, and with a feedback resistor, R
f
=
20 k
, the value of R
i
follows from equation (7).
R
i
= R
f
(A
V
1)
Thus with R
= 1 k
a non-inverting gain of 21 will result.
Since the desired input impedance was 47 k
, a value of 47
k
was selected for R
. 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 bet-
ter than the required
±
0.25 dB specified. This fact results in
a low and high frequency pole of 4 Hz and 100 kHz respec-
tively. As stated in the
External Components
section, R
i
in
conjunction with C
i
create a high-pass filter.
C
i
≥
1/(2
π
*
1 k
*
4 Hz) = 39.8 μF;
The high frequency pole is determined by the product of the
desired high frequency pole, f
, and the gain, A
. With a
A
= 21 and f
= 100 kHz, the resulting GBWP is 2.1 MHz,
which is less than the guaranteed minimum GBWP of the
LM1876 of 5 MHz. This will ensure that the high frequency
response of the amplifier will be no worse than 0.17 dB down
at 20 kHz which is well within the bandwidth requirements of
the design.
A
V
≥
11.
(7)
use 39 μF.
www.national.com
14
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM1876TF | 制造商:Texas Instruments 功能描述:IC AMP AUDIO DUAL 20W |
| LM1876TF/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 |
| LM1877 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dual Audio Power Amplifier |
| LM1877M-9 | 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 |
| LM1877M-9/NOPB | 功能描述:音頻放大器 DUAL AUDIO POWER AMP 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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