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參數資料
| 型號： | LM4862 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 675 mW Audio Power Amplifier with Shutdown Mode |
| 中文描述： | 675毫瓦音頻功率放大器關斷模式 |
| 文件頁數： | 7/10頁 |
| 文件大小： | 262K |
| 代理商： | LM4862 |
Application Information
(Continued)
The
Automatic Switching Circuit
is based upon a single
control pin common in many headphone jacks which forms a
normally closed switch with one of the output pins. The out-
put of this circuit (the voltage on pin 5 of the LM4880) has
two states based on the position of the switch. When the
switch inside the headphone jack is open, the LM4880 is en-
abled and the LM4862 is disabled since the NMOS inverter
is on. If a headphone jack is not present, it is assumed that
the internal speakers should be on and the external speak-
ers should be off. Thus the voltage on the LM4862 shutdown
pin is low and the voltage on the LM4880 shutdown pin is
high.
The operation of this circuit is rather simple. With the switch
closed, R
and R
form a resistor divider which produces a
gate voltage of less than 50 mV. The gate voltage keeps the
NMOS inverter off and R
pulls the shutdown pin of the
LM4880 to the supply voltage. This shuts down the LM4880
and places the LM4862 in its normal mode of operation.
When the switch is open, the opposite condition is produced.
Resistor R
pulls the gate of the NMOS high which turns on
the inverter and produces a logic low signal on the shutdown
pin of the LM4880. This state enables the LM4880 and
places the LM4862 in shutdown mode.
Only one channel of this circuit is shown in Figure 2 to keep
the drawing simple but a typical application would be a
LM4880 driving a stereo headphone jack and two LM4862’s
driving a pair of internal speakers. If a single internal speaker
is required, one LM4862 can be used as a summer to mix
the left and right inputs into a mono channel.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications us-
ing integrated power amplifiers is critical to optimize device
and system performance. While the LM4862 is tolerant of
external component combinations, consideration to compo-
nent values must be used to maximize overall system qual-
ity.
The LM4862 is unity-gain stable which gives a designer
maximum system flexibility. The LM4862 should be used in
low gain configurations to minimize THD+N values, and
maximize the signal to noise ratio. Low gain configurations
require large input signals to obtain a given output power. In-
put signals equal to or greater than 1 Vrms are available
from sources such as audio codecs. Please refer to the sec-
tion,
Audio Power Amplifier Design
, for a more complete
explanation of proper gain selection.
Besides gain, one of the major considerations is the
closed-loop bandwidth of the amplifier. To a large extent, the
band-width is dictated by the choice of external components
shown in Figure 1 The input coupling capacitor, C
, forms a
first order high pass filter which limits low frequency re-
sponse. This value should be chosen based on needed fre-
quency response for a few distinct reasons.
Selection of Input Capacitor Size
Large input capacitors are both expensive and space hungry
for portable designs. Clearly, a certain sized capacitor is
needed to couple in low frequencies without severe attenua-
tion. But in many cases the speakers used in portable sys-
tems, whether internal or external, have little ability to repro-
duce signals below 100–150 Hz. Thus using a large input
capacitor may not increase system performance.
In addition to system cost and size, click and pop perfor-
mance is effected by the size of the input coupling capacitor,
C
. A larger input coupling capacitor requires more charge to
reach its quiescent DC voltage (nominally
charge comes from the output via the feedback and is apt to
create pops upon device enable. Thus, by minimizing the ca-
pacitor size based on necessary low frequency response,
turn-on pops can be minimized.
Besides minimizing the input capacitor size, careful consid-
eration should be paid to the bypass capacitor value. Bypass
capacitor, C
, is the most critical component to minimize
turn-on pops since it determines how fast the LM4862 turns
on. The slower the LM4862’s outputs ramp to their quiescent
DC voltage (nominally
1
2
V
), the smaller the turn-on pop.
Choosing C
equal to 1.0 μF along with a small value of C
i
(in the range of 0.1 μF to 0.39 μF), should produce a virtually
clickless and popless shutdown function. While the device
will function properly, (no oscillations or motorboating), with
C
equal to 0.1 μF, the device will be much more susceptible
to turn-on clicks and pops. Thus, a value of C
equal to
1.0 μF or larger is recommended in all but the most cost sen-
sitive designs.
1
2
V
). This
www.national.com
7
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PDF描述 |
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| LM4862M | 675 mW Audio Power Amplifier with Shutdown Mode |
| LM4863 | Dual 2.2W Audio Amplifier Plus Stereo Headphone Function |
| LM4863M | Dual 2.2W Audio Amplifier Plus Stereo Headphone Function |
| LM4863MT | Dual 2.2W Audio Amplifier Plus Stereo Headphone Function |
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LM4862G-D08-T | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:AUDIO POWER AMPLIFIER WITH SHUTDOWN MODE |
| LM4862G-S08-R | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:AUDIO POWER AMPLIFIER WITH SHUTDOWN MODE |
| LM4862L-D08-T | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:AUDIO POWER AMPLIFIER WITH SHUTDOWN MODE |
| LM4862L-S08-R | 制造商:UTC-IC 制造商全稱:UTC-IC 功能描述:AUDIO POWER AMPLIFIER WITH SHUTDOWN MODE |
| LM4862M | 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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