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參數(shù)資料
| 型號： | LM4766MDC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 40 W, 2 CHANNEL, AUDIO AMPLIFIER, UUC |
| 封裝： | DIE |
| 文件頁數(shù)： | 4/17頁 |
| 文件大?。?/td> | 534K |
| 代理商： | LM4766MDC |
Application Information (Continued)
If adequate bypassing is not provided, the current in the
supply leads which is a rectified component of the load
current may be fed back into internal circuitry. This signal
causes distortion at high frequencies requiring that the sup-
plies be bypassed at the package terminals with an electro-
lytic capacitor of 470F or more.
BRIDGED AMPLIFIER APPLICATION
The LM4766 has two operational amplifiers internally, allow-
ing for a few different amplifier configurations. One of these
configurations is referred to as “bridged mode” and involves
driving the load differentially through the LM4766’s outputs.
This configuration is shown in
Figure 2. Bridged mode op-
eration is different from the classical single-ended amplifier
configuration where one side of its load is connected to
ground.
A bridge amplifier design has a distinct advantage over the
single-ended configuration, as it provides differential drive to
the load, thus doubling output swing for a specified supply
voltage. Consequently, theoretically four times the output
power is possible as compared to a single-ended amplifier
under the same conditions. This increase in attainable output
power assumes that the amplifier is not current limited or
clipped.
A direct consequence of the increased power delivered to
the load by a bridge amplifier is an increase in internal power
dissipation. For each operational amplifier in a bridge con-
figuration, the internal power dissipation will increase by a
factor of two over the single ended dissipation. Thus, for an
audio power amplifier such as the LM4766, which has two
operational amplifiers in one package, the package dissipa-
tion will increase by a factor of four. To calculate the
LM4766’s maximum power dissipation point for a bridged
load, multiply
Equation (1) by a factor of four.
This value of P
DMAX can be used to calculate the correct size
heat sink for a bridged amplifier application. Since the inter-
nal dissipation for a given power supply and load is in-
creased by using bridged-mode, the heatsink’s
θ
SA will have
to decrease accordingly as shown by
Equation (3). Refer to
the section, Determining the Correct Heat Sink, for a more
detailed discussion of proper heat sinking for a given appli-
cation.
SINGLE-SUPPLY AMPLIFIER APPLICATION
The typical application of the LM4766 is a split supply am-
plifier. But as shown in
Figure 3, the LM4766 can also be
used in a single power supply configuration. This involves
using some external components to create a half-supply bias
which is used as the reference for the inputs and outputs.
Thus, the signal will swing around half-supply much like it
swings around ground in a split-supply application. Along
with proper circuit biasing, a few other considerations must
be accounted for to take advantage of all of the LM4766
functions, like the mute function.
CLICKS AND POPS
In the typical application of the LM4766 as a split-supply
audio power amplifier, the IC exhibits excellent “click” and
“pop” performance when utilizing the mute and standby
modes. In addition, the device employs Under-Voltage Pro-
tection,
which
eliminates
unwanted
power-up
and
power-down transients. The basis for these functions are a
stable and constant half-supply potential. In a split-supply
application, ground is the stable half-supply potential. But in
a single-supply application, the half-supply needs to charge
up just like the supply rail, V
CC. This makes the task of
attaining a clickless and popless turn-on more challenging.
Any uneven charging of the amplifier inputs will result in
output clicks and pops due to the differential input topology
of the LM4766.
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 LM4766. In
Figure 3, the resistor R
INP
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
BI help bias up
the LM4766 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
BI, namely 10k and 200k. These
resistors bring up the inputs at the same rate resulting in a
popless turn-on. Adjusting these resistors values slightly
may reduce pops resulting from power supplies that ramp
extremely quick or exhibit overshoot during system turn-on.
AUDIO POWER AMPLlFIER DESIGN
Design a 30W/8
Audio Amplifier
Given:
Power Output
30Wrms
Load Impedance
8
Input Level
1Vrms(max)
Input Impedance
47k
Bandwidth
20Hz20kHz
±0.25dB
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
OPEAK can be determined from
Equation (4) and I
OPEAK from Equation (5).
(4)
(5)
To determine the maximum supply voltage the following
conditions must be considered. Add the dropout voltage to
the peak output swing V
OPEAK, to get the supply rail at a
current of I
OPEAK. The regulation of the supply determines
the unloaded voltage which is usually about 15% higher. The
supply voltage will also rise 10% during high line conditions.
Therefore the maximum supply voltage is obtained from the
following equation.
Max supplies
≈ ± (V
OPEAK +VOD) (1 + regulation) (1.1)
For 30W of output power into an 8
load, the required
V
OPEAK is 21.91V. A minimum supply rail of 25.4V results
from adding V
OPEAK and VOD. With regulation, the maximum
supplies are ±32V and the required I
OPEAK is 2.74A from
Equation (5). It should be noted that for a dual 30W amplifier
into an 8
load the I
OPEAK drawn from the supplies is twice
2.74A
PK or 5.48APK. 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. In addition, the designer should
LM4766
www.national.com
12
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| LM4808MDC | 0.15 W, 2 CHANNEL, AUDIO AMPLIFIER, UUC |
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4766T | 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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4766T | 制造商:Texas Instruments 功能描述:IC AMP DUAL 40W 4766 TO-220-15 |
| LM4766T/LF15 | 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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4766T/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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4766TF | 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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
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