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參數(shù)資料
| 型號： | LM4916MM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 1.5V, Mono 85mW BTL Output, 14mW Stereo Headphone Audio Amplifier |
| 中文描述： | 0.014 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 |
| 封裝： | MSOP-10 |
| 文件頁數(shù)： | 15/18頁 |
| 文件大小： | 655K |
| 代理商： | LM4916MM |
Application Information
(Continued)
limited frequency response reap little improvement by using
a high value input capacitor. In addition to system cost and
size, turn on time is affected by the size of the input coupling
capacitor C
i
. A larger input coupling capacitor requires more
charge to reach its quiescent DC voltage. This charge
comes from the output via the feedback. Thus, by minimizing
the capacitor size based on necessary low frequency re-
sponse, turn-on time can be minimized. A small value of C
i
(in the range of 0.1μF to 0.47μF), is recommended.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consid-
eration should be paid to value of C
B
, the capacitor con-
nected to the BYPASS pin. Since C
determines how fast
the LM4916 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4916’s
outputs ramp to their quiescent DC voltage (nominally V
/
2), the smaller the turn-on pop. Choosing C
equal to 4.7μF
along with a small value of C
(in the range of 0.1μF to
0.47μF), produces a click-less and pop-less shutdown func-
tion. As discussed above, choosing C
no larger than neces-
sary for the desired bandwidth helps minimize clicks and
pops. This ensures that output transients are eliminated
when power is first applied or the LM4916 resumes opera-
tion after shutdown.
Minimizing External Components
Operating the LM4916 at higher gain settings can minimize
the use of external components. For instance, a BTL con-
figuration with a gain setting greater than 8V/V (A
V
>
8)
makes the output capacitor C
O
unnecessary. For the Single
Ended configuration, a gain setting greater than 4V/V (A
>
4) eliminates the need for output capacitor C
O2
and output
resistor R
O
, on each output channel.
If the LM4916 is operating with a lower gain setting (A
<
4),
external components can be further minimized only in Single
Ended mode. For each channel, output capacitor (C
) and
output resistor (R
) can be eliminated. These components
need to be compensated for by adding a 7.5k
resistor (R
)
between the input pin and ground pin on each channel
(between Pin 1 and GND, and between Pin 5 and GND).
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4916 contains circuitry that eliminates turn-on and
shutdown transients ("clicks and pops"). For this discussion,
turn-on refers to either applying the power supply voltage or
when the micro-power shutdown mode is deactivated.
As the V
/2 voltage present at the BYPASS pin ramps to its
final value, the LM4916’s internal amplifiers are configured
as unity gain buffers. An internal current source charges the
capacitor connected between the BYPASS pin and GND in a
controlled, linear manner. Ideally, the input and outputs track
the voltage applied to the BYPASS pin. The gain of the
internal amplifiers remains unity until the voltage on the
bypass pin reaches V
DD
/2. As soon as the voltage on the
bypass pin is stable, the device becomes fully operational
and the amplifier outputs are reconnected to their respective
output pins. Although the BYPASS pin current cannot be
modified, changing the size of C
alters the device’s turn-on
time. There is a linear relationship between the size of C
B
and the turn-on time. Here are some typical turn-on times for
various values of C
B
:
Single-Ended
C
B
(μF)
0.1
0.22
0.47
1.0
2.2
4.7
T
ON
117ms
179ms
310ms
552ms
1.14s
2.4s
BTL
C
B
(μF)
0.1
0.22
0.47
1.0
2.2
4.7
T
ON
(ms)
72
79
89
112
163
283
In order to eliminate "clicks and pops", all capacitors must be
discharged before turn-on. Rapidly switching V
may not
allow the capacitors to fully discharge, which may cause
"clicks and pops".
AUDIO POWER AMPLIFIER DESIGN
A 25mW/32
Audio Amplifier
Given:
Power Output
Load Impedance
Input Level
Input Impedance
A designer must first choose a mode of operation (SE or
BTL) and determine the minimum supply rail to obtain the
specified output power. By extrapolating from the Output
Power vs. Supply Voltage graphs in the Typical Performance
Characteristics section, the supply rail can be easily found.
1.5V is a standard voltage in most applications, it is chosen
for the supply rail. Extra supply voltage creates headroom
that allows the LM4916 to reproduce peak in excess of
10mW without producing audible distortion. At this time, the
designer must make sure that the power supply choice along
with the output impedance does not violate the conditions
explained in the Power Dissipation section. Once the power
dissipation equations have been addressed, the required
gain can be determined from Equation 2.
10mWrms
16
0.4Vrms
20k
(4)
From Equation 4, the minimumAV is 1; useA
V
= 1. Since the
desired input impedance is 20k, and with a A
gain of 1, a
ratio of 1:1 results from Equation 1 for R
to R. The values
are chosen with R
= 20k and R
= 20k. The final design step
is to address the bandwidth requirements which must be
stated as a pair of -3dB frequency points. Five times away
from a -3dB point is 0.17dB down from passband response
which is better than the required
±
0.25dB specified.
L
www.national.com
15
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相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4916MM/NOPB | 功能描述:音頻放大器 10Mw Stereo Headphone Audio Amp 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 |
| LM4916MMX | 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 |
| LM4916MMX/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 |
| LM4917 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Ground-Referenced, 95mW Stereo Headphone Amplifier |
| LM4917MT | 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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