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參數(shù)資料
| 型號： | LM4854MM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 0.2 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 |
| 封裝： | 0.118 INCH, 0.50 MM PITCH, TSSOP-10 |
| 文件頁數(shù)： | 8/23頁 |
| 文件大?。?/td> | 1795K |
| 代理商： | LM4854MM |
Application Information (Continued)
AMP3 changes from shutdown state to an active state and,
along with AMP1, drives a stereo load. AMP2 drives the
headphone jack sleeve.
Figure 3 shows the suggested headphone jack electrical
connections. The jack is designed to mate with a three-wire
plug. The plug’s tip should carry a stereo signal’s left-
channel information. The ring adjacent to the tip should each
carry the right-channel signal and the ring furthest from the
tip provides the return to AMP2. A switch can replace the
headphone jack contact pin. When the switch shorts the
HP-SENSE pin to R-OUT, the bridge-connected speaker is
driven by AMP1 and AMP2. AMP3 is shutdown, its output in
a high-impedance state. When the switch opens, the
LM4854 operates in SE stereo mode. If headphone drive is
not needed, short the HP-SENSE pin to the R-OUT pin.
The LM4854’s unique headphone sense circuit requires a
dual switch headphone jack. A five-terminal headphone jack,
such as the Switchcraft 35RAPC4BH3, is shown in Figure 2.
For applications that require an SPDIF interface in the stereo
headphone jack, use a Foxconn 2F1138-TJ-TR.
Single-Ended Output Power Performance and Measure-
ment Considerations
The LM4854 delivers clean, low distortion SE output power
into loads that are greater than 10
. As an example, output
power for 16
and 32 loads are shown in the Typical
Performance Characteristic curves. For loads less than 10
,
the LM4854 can typically supply 180mW of low distortion
power. However, when higher dissipation is desired in loads
less than 10
, a dramatic increase in THD+N may occur.
This is normal operation and does not indicate that proper
functionality has ceased. When a jump from moderate to
excessively high distortion is seen, simply reducing the out-
put voltage swing will restore the clean, low distortion SE
operation.
The dramatic jump in distortion for loads less than 10
occurs when current limiting circuitry activates. During SE
operation, AMP2 (refer to Figure 2) drives the headphone
sleeve. An on-board circuit monitors this amplifier’s output
current. The sudden increase in THD+N is caused by the
current limit circuitry forcing AMP2 into a high-impedance
output mode. When this occurs, the output waveform has
discontinuities that produce large amounts of distortion. It
has been observed that as the output power is steadily
increased, the distortion may jump from 5% to greater than
35%. Indeed, 10% THD+N may not actually be achievable.
ESD Protection
As stated in the Absolute Maximum Ratings, pin 3C has a
maximum ESD susceptibility rating of 8000V. For higher
ESD voltages, the addition of an ESDAxxxL dual transil, as
shown in Figure 4, will provide additional protection. For V
DD
= 3V, use the ESDA5V3L and for V
DD
= 5V, use the
ESDA6V3L. Consult SGS-Thomson for an ESDAxxxL
datasheet. It specifies the absolute maximum ESD voltages
against which the transil array is designed protect.
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitor (Ci in Figure 2). 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.
The LM4854’s advanced output transient suppression cir-
cuitry has eliminated the need to select the input capacitor’s
value in relation to the BYPASS capacitor’s value as was
necessary in some previous Boomer amplifiers. The value of
CI is now strictly determined by the desired low frequency
response.
As shown in Figure 2, the input resistor (R
i) and the input
capacitor (C
i) produce a high pass filter cutoff frequency that
is found using Equation (7).
f
c =1/(2πRiCi)
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, C
i, using Equation (7) is 0.063F. The 1.0F
C
i shown in Figure 2 allows the LM4854 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 CB, the capacitor con-
nected to the BYPASS pin. Since C
B determines how fast
the LM4854 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4854’s
outputs ramp to their quiescent DC voltage (nominally V
DD/
2), the smaller the turn-on pop. Choosing C
B equal to 1.0F
20038212
FIGURE 3. Headphone Circuit
200382A4
FIGURE 4. The ESDAxxxL Provides additional ESD
pretection beyond the 8000V shown in the Absolute
Maximum Ratings for the AMP2 output
LM4854
www.national.com
16
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4854MT | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM4854MT/NOPB | 功能描述:IC AMP AUDIO PWR 2.3W AB 14TSSOP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機(jī)，2-通道（立體聲） 在某負(fù)載時(shí)最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點(diǎn):I²C，麥克風(fēng)，靜音，短路保護(hù)，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4854MTX/NOPB | 功能描述:IC AMP AUDIO PWR 2.3W AB 14TSSOP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機(jī)，2-通道（立體聲） 在某負(fù)載時(shí)最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點(diǎn):I²C，麥克風(fēng)，靜音，短路保護(hù)，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4855 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Boomer AUDIO POWER AMPLIFIER Integrated Audio Amplifier System |
| LM48555 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Ceramic Speaker Driver |
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