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参数资料
| 型号： | LM4700T |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 30 W, 1 CHANNEL, AUDIO AMPLIFIER, PZFM11 |
| 封装： | TO-220, 11 PIN |
| 文件页数： | 9/19页 |
| 文件大小： | 997K |
| 代理商： | LM4700T |
Application Information (Continued)
passing utilizing a large tantalum or electrolytic capacitor (10
F or larger) which is used to absorb low frequency varia-
tions and a small ceramic capacitor (0.1 F) to prevent any
high frequency feedback through the power supply lines.
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 470 F or more.
BRIDGED AMPLIFIER APPLICATION
One common power amplifier configuration is shown in Fig-
ure 2 and is referred to as “bridged mode” operation. Bridged
mode operation is different from the classical single-ended
amplifier configuration where one side of the output 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. Since there
are two amplifiers used in a bridge configuration, the maxi-
mum system power dissipation point will increase by a factor
of four over the figure obtained by equation (1).
This value of P
DMAX can be used to calculate the correct size
heat sink for a bridged amplifier application, assuming that
both IC’s are mounted on the same heatsink. Since the
internal dissipation for a given power supply and load is
increased 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 application.
SINGLE-SUPPLY AMPLIFIER APPLICATION
The typical application of the LM4700 is a split supply am-
plifier. But as shown in Figure 3, the LM4700 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 LM4700
functions.
The LM4700 possesses a mute and standby function with
internal logic gates that are half-supply referenced. Thus, to
enable either the mute or standby function, the voltage at
these pins must be a minimum of 2.5V above half-supply. In
single-supply systems, devices such as microprocessors
and simple logic circuits used to control the mute and
standby functions, are usually referenced to ground, not
half-supply. Thus, to use these devices to control the logic
circuitry of the LM4700, a “level shifter”, like the one shown
in Figure 5, must be employed. A level shifter is not needed
in a split-supply configuration since ground is also half-
supply.
When the voltage at the Logic Input node is 0V, the 2N3904
is “off” and thus resistor R
C pulls up mute or standby input to
the supply. This enables the mute or standby function. When
the Logic Input is 5V, the 2N3904 is “on” and consequently,
the voltage at the collector is essentially 0V. This will disable
the mute or standby function, and thus the amplifier will be in
its normal mode of operation. R
SHIFT, along with CSHIFT,
creates an RC time constant that reduces transients when
the mute or standby functions are enabled or disabled. Ad-
ditionally, R
SHIFT limits the current supplied by the internal
logic gates of the LM4700 which insures device reliability.
Refer to the Mute Mode and Standby Mode sections in the
Application Information section for a more detailed de-
scription of these functions.
CLICKS AND POPS
In the typical application of the LM4700 as a split-supply
audio power amplifier, the IC exhibits excellent “click” and
“pop” performance when utilizing the mute and standby func-
tions. In addition, the device employs Under-Voltage Protec-
tion, 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 am-
plifier inputs will result in output clicks and pops due to the
differential input topology of the LM4700.
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 LM4700. 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 upon a specific application loading and thus, the
system designer may need to adjust these values for opti-
mum performance.
As shown in Figure 3, the resistors labeled R
BI help bias up
the LM4700 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 10 k
and 200 k. These
resistors bring up the inputs at the same rate resulting in a
popless turn-on. Adjusting these resistors values slightly
01236909
FIGURE 5. Level Shift Circuit
LM4700
www.national.com
17
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PDF描述 |
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| LM4700TF/NOPB | 30 W, 1 CHANNEL, AUDIO AMPLIFIER, PZFM11 |
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM4700T/NOPB | 制造商:Texas Instruments 功能描述: |
| LM4700TF | 制造商:Texas Instruments 功能描述:IC AMP + MUTE 30W 4700 TO-220-11 |
| LM4700TF | 制造商:Texas Instruments 功能描述:IC AMP + MUTE 30W 4700 TO-220-11 |
| LM4700TF/NOPB | 功能描述:IC AMP AUDIO PWR 30W AB TO220-11 RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Overture™ 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR) |
| LM4701 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:LM4701 Overture⑩ Audio Power Amplifier Series 30W Audio Power Amplifier with Mute and Standby Modes |
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