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參數資料
| 型號： | LM4867 |
| 廠商： | National Semiconductor Corporation |
| 元件分類： | 音頻放大器 |
| 英文描述： | Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
| 中文描述： | 輸出瞬態免費雙2.1W音頻放大器加上沒有耦合電容器立體聲耳機功能 |
| 文件頁數： | 15/26頁 |
| 文件大小： | 763K |
| 代理商： | LM4867 |
Application Information
(Continued)
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitor (C
i
in Figure 4). A high value capaci-
tor can be expensive and may compromise space efficiency
in portable designs. In many cases, however, the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 150Hz. Applications
using speakers with this limited frequency response reap
little improvement by using large input capacitor.
Besides effecting system cost and size, C
has an affect on
the LM4867’s click and pop performance. When the supply
voltage is first applied, a transient (pop) is created as the
charge on the input capacitor changes from zero to a quies-
cent state. The magnitude of the pop is directly proportional
to the input capacitor’s size. Higher value capacitors need
more time to reach a quiescent DC voltage (usually V
/2)
when charged with a fixed current. The amplifier’s output
charges the input capacitor through the feedback resistor,
R
. Thus, pops can be minimized by selecting an input
capacitor value that is no higher than necessary to meet the
desired 3dB frequency and is between 0.14C
B
and 0.20C
B
.
A shown in Figure 4 the input resistor (R
) and the input
capacitor, C
produce a 3dB high pass filter cutoff frequency
that is found using Equation (7).
f
3dB
= 1/(2
π
R
IN
C
I
)
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, C
i
, using Equation (4) is 0.063μF. The 1.0μF
C
i
shown in Figure 4 allows the LM4867 to drive high effi-
ciency, full range speaker whose response extends below
30Hz.
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 LM4867 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4867’s
outputs ramp to their quiescent DC voltage (nominally 1/2
V
), the smaller the turn-on pop. Choosing C
equal to
1.0μF along with a small value of C
(in the range of 0.1μF to
0.39μF), produces a click-less and pop-less shutdown func-
tion. As discussed above, choosing C
i
no larger than neces-
sary for the desired bandwidth helps minimize clicks and
pops. C
B
’s value should be in the range of 5 times to 7 times
the value of C
i
. This ensures that output transients are
eliminated when power is first applied or the LM4867 re-
sumes operation after shutdown.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4867 contains circuitry that eliminates turn-on and
shutdown transients (“clicks and pops“) and transients that
could occur when switching between BTL speakers and
single-ended headphones. For this discussion, turn-on re-
fers to either applying the power supply voltage or when the
shutdown mode is deactivated. While the power supply is
ramping to its final value, the LM4867’s internal amplifiers
are configured as unity gain buffers and are disconnected
from the -OUT and +OUT pins. An internal current source
changes the voltage of the BYPASS pin in a controlled,
linear manner. Ideally, the input and outputs track the voltage
applied to the BYPASS pin. The gain of the internal amplifi-
ers remains unity until the voltage on the bypass pin reaches
1/2 V
. As soon as the voltage on the bypass pin is stable,
the device becomes fully operational and the amplifier out-
puts are reconnected to the -OUT and +OUT 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
and the turn-on time.
Here are some typical turn-on times for various values of C
B
:
C
B
0.01μF
0.1μF
0.22μF
0.47μF
1.0μF
2.2μF
T
ON
3ms
30ms
63ms
134ms
300ms
630ms
In order 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“.
DS200013-24
FIGURE 7. Headphone Circuit
(Pin numbers in ( ) are for the 20-pin MTE and MT packages.)
L
www.national.com
15
相關PDF資料 |
PDF描述 |
|---|---|
| LM4867LQ | Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
| LM4867MT | Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
| LM4867MTE | Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
| LM4868 | Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
| LM4868MTE | Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
相關代理商/技術參數 |
參數描述 |
|---|---|
| LM4867_02 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Output-Transient-Free Dual 2.1W Audop Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
| LM4867A E WAF | 制造商:Texas Instruments 功能描述: |
| LM4867LQ | 功能描述:IC AMP AUDIO PWR 3W STER 24LLP RoHS:否 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產品培訓模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機，2-通道（立體聲） 在某負載時最大輸出功率 x 通道數量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應商設備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4867LQ/NOPB | 制造商:Texas Instruments 功能描述:Audio Amp Headphone/Speaker 2-CH Stereo 3W Class-AB 24-Pin LLP EP T/R |
| LM4867MT | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
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