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參數(shù)資料
| 型號： | LM4875MMX/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻控制 |
| 英文描述： | 1 CHANNEL(S), VOLUME CONTROL CIRCUIT, PDSO8 |
| 封裝： | 0.118 INCH, MSOP-8 |
| 文件頁數(shù)： | 12/15頁 |
| 文件大小： | 664K |
| 代理商： | LM4875MMX/NOPB |
Application Information (Continued)
Another advantage of the differential bridge output is no net
DC voltage across load. This results from biasing V
O1 and
V
O2 at half-supply. This eliminates the coupling capacitor
that single supply, single-ended amplifiers require. Eliminat-
ing an output coupling capacitor in a single-ended configu-
ration forces a single supply amplifier’s half-supply bias volt-
age across the load. The current flow created by the
half-supply bias voltage increases internal IC power dissipa-
tion and may permanently damage loads such as speakers.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful bridged or single-ended amplifier. Equation (1)
states
the
maximum
power
dissipation
point
for
a
single-ended amplifier operating at a given supply voltage
and driving a specified output load.
P
DMAX =(VDD)
2/(2
π2R
L)
Single-Ended
(1)
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is an increase in
internal power dissipation point for a bridge amplifier oper-
ating at the same given conditions.
P
DMAX = 4*(VDD)
2/(2
π2R
L)
Bridge Mode
(2)
The LM4875 has two operational amplifiers in one package
and the maximum internal power dissipation is 4 times that
of a single-ended amplifier. However, even with this substan-
tial increase in power dissipation, the LM4875 does not
require heatsinking. From Equation (2), assuming a 5V
power supply and an 8
load, the maximum power dissipa-
tion point is 633 mW. The maximum power dissipation point
obtained from Equation (2) must not be greater than the
power dissipation that results from Equation (3):
P
DMAX =(TJMAX–TA)/θJA
(3)
For the SO package,
θ
JA = 150C/W. The MSOP package
has a 190C/W
θ
JA.TJMAX = 150C for the LM4875. For a
given ambient temperature T
A, Equation (3) can be used to
find the maximum internal power dissipation supported by
the IC packaging. If the result of Equation (2) is greater than
that of Equation (3), then either decrease the supply voltage,
increase the load impedance, or reduce the ambient tem-
perature. For a typical application using the SO packaged
LM4875, a 5V power supply, and an 8
load, the maximum
ambient temperature that does not violate the maximum
junction temperature is approximately 55C. The maximum
ambient temperature for the MSOP package with the same
conditions is approximately 30C. These results further as-
sume that a device is a surface mount part operating around
the maximum power dissipation point. Since internal power
dissipation is a function of output power, higher ambient
temperatures are allowed as output power decreases. Refer
to the Typical Performance Characteristics curves for
power dissipation information at lower output power levels.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. The capacitors connected to the bypass and power
supply pins should be placed as close to the LM4875 as
possible. The capacitor connected between the bypass pin
and ground improves the internal bias voltage’s stability,
producing improved PSRR. The improvements to PSRR
increase as the bypass pin capacitor value increases. Typi-
cal applications employ a 5V regulator with 10F and a
0.1F filter capacitors that aid in supply stability. Their pres-
ence, however does not eliminate the need for bypassing the
supply nodes of the LM4875. The selection of bypass ca-
pacitor values, especially C
B, depends on desired PSRR
requirements, click and pop performance (as explained in
the section, Proper Selection of External Components),
system cost, and size constraints.
DC VOLTAGE VOLUME CONTROL
The LM4875’s internal volume control is controlled by the DC
voltage applied its DC Vol/SD pin (pin 4). The volume con-
trol’s input range is from GND to V
DD. A graph showing a
typical volume response versus input control voltage is
shown in the Typical Performance Characteristicssection.
The DC Vol/SD pin also functions as the control pin for the
LM4875’s micropower shutdown feature. See the Mute and
Shutdown Function section for more information.
Like all volume controls, the Lm4875’s internal volume con-
trol is set while listening to an amplified signal that is applied
to an external speaker. The actual voltage applied to the DC
Vol/SD pin is a result of the volume a listener desires. As
such, the volume control is designed for use in a feedback
system that includes human ears and preferences. This
feedback system operates quite well without the need for
accurate gain. The user simply sets the volume to the de-
sired level as determined by their ear, without regard to the
actual DC voltage that produces the volume. Therefore, the
accuracy of the volume control is not critical, as long as
volume changes monotonically and step size is small
enough to reach a desired volume that is not too loud or too
soft. Since gain accuracy is not critical, there may be a
volume variation from part-to-part even with the same ap-
plied DC control voltage. The gain of a given LM4875 can be
set with a fixed external voltage, but another LM4875 may
require a different control voltage to achieve the same gain.
Figure 2 is a curve showing the volume variation of seven
typical LM4875s as the voltage applied to the DC Vol/SD pin
is varied. For gains between -20dB and +16dB, the typical
part-to-part variation is typically ±1dB for a given control
voltage.
MUTE AND SHUTDOWN FUNCTION
The LM4875’s mute and shutdown functions are controlled
through the DC Vol/SD pin. Mute is activated by applying a
voltage in the range of 500mV to 1V. A typical attenuation of
75dB is achieved is while mute is active. The LM4875’s
micropower shutdown mode turns off the amplifier’s bias
circuitry. The micropower shutdown mode is activated by
DS101042-48
FIGURE 2. Typical part-to-part gain variation as a
function of DC-Vol control voltage
LM4875
www.national.com
6
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4875MX | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產品: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 |
| LM4875MX/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產品: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 |
| LM4876 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1.1W Audio Power Amplifier with Logic Low Shutdown |
| LM4876_03 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1.1W Audio Power Amplifier with Logic Low Shutdown |
| LM4876M | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產品: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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