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参数资料
| 型号： | LM4865MDC |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频控制 |
| 英文描述： | 1 CHANNEL(S), VOLUME CONTROL CIRCUIT, UUC |
| 封装： | DIE |
| 文件页数： | 15/18页 |
| 文件大小： | 520K |
| 代理商： | LM4865MDC |
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 LM4865 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 LM4865 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 micro SMD and SO packages,
θ
JA = 150C/W. The
MSO package has a 190C/W
θ
JA.TJMAX = 150C for the
LM4865. 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 temperature. For a typical application using the
micro SMD or SO packaged LM4865, a 5V power supply,
and an 8
load, the maximum ambient temperature that
does not violate the maximum junction temperature is ap-
proximately 55C. The maximum ambient temperature for
the MSO package with the same conditions is approximately
30C. These results further assume 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 Char-
acteristics 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 LM4865 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 LM4865. 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 LM4865 has internal volume control that is controlled by
the DC voltage applied its DC Vol/SD pin (pin 5 on the micro
SMD and pin 4 on the MSOP and SOP packages). The
volume control’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 Characteris-
ticssection. The DC Vol/SD pin also functions as the control
pin for the LM4865’s micropower shutdown feature. See
theShutdown Function section for more information.
Like all volume controls, the LM4865’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 will be volume
variation from part-to-part even with the same applied DC
control voltage. The gain of a given LM4865 can be set with
a fixed external voltage, but another LM4865 may require a
different control voltage to achieve the same gain.
Figure 2 is
a curve showing the volume variation of twenty typical
LM4865s as the voltage applied to the DC Vol/SD pin is
varied. For gains greater than unity, the typical part-to-part
variation can be as large as 8dB for the same control
voltage.
MUTE AND SHUTDOWN FUNCTION
The LM4865’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 LM4865’s
micropower shutdown mode turns off the amplifier’s bias
circuitry. The micropower shutdown mode is activated by
DS101025-47
FIGURE 2. Typical part-to-part gain variation as a
function of DC-Vol control voltage
LM4865
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| LM4865MM | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| LM4865MM/NOPB | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| LM4865MMX | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| LM4865MMX/NOPB | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| LM4865MX | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
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