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參數(shù)資料
| 型號： | LM4883SQ/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 0.4 W, 2 CHANNEL, AUDIO AMPLIFIER, QCC24 |
| 封裝： | LLP-24 |
| 文件頁數(shù)： | 9/23頁 |
| 文件大?。?/td> | 1244K |
| 代理商： | LM4883SQ/NOPB |
Application Information (Continued)
placing the LM4883 in bridged mode operation. The output
coupling capacitor blocks the amplifier’s half supply DC volt-
age, protecting the headphones.
The HP-IN threshold is set at 4V. While the LM4883 operates
in bridged mode, the DC potential across the load is essen-
tially 0V. Therefore, even in an ideal situation, the output
swing cannot cause a false single-ended trigger. Connecting
headphones to the headphone jack disconnects the head-
phone jack contact pin from OUTA and allows R1 to pull the
HP Sense pin up to V
DD. This enables the headphone func-
tion, turns off Amp A (+out) and Amp B (+out) which mutes
the bridged speaker. The amplifier then drives the head-
phones, whose impedance is in parallel with resistors R11
and R12. These resistors have negligible effect on the
LM4883’s output drive capability since the typical impedance
of headphones is 32
.
Figure 4 also shows the suggested headphone jack electri-
cal connections. The jack is designed to mate with a three-
wire plug. The plug’s tip and ring should each carry one of
the two stereo output signals, whereas the sleeve should
carry the ground return. A headphone jack with one control
pin contact is sufficient to drive the HP-IN pin when connect-
ing headphones.
A microprocessor or a switch can replace the headphone
jack contact pin. When a microprocessor or switch applies a
voltage greater than 4V to the HP-IN pin, a bridge-connected
speaker is muted and Amp A (-out) and Amp B (-out) drive a
pair of headphones.
SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the LM4883’s performance requires properly se-
lecting external components. Though the LM4883 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
The LM4883 is unity-gain stable, giving a designer maximum
design flexibility. The gain should be set to no more than a
given application requires. This allows the amplifier to
achieve minimum THD+N and maximum signal-to-noise ra-
tio. These parameters are compromised as the closed-loop
gain increases. However, low gain demands input signals
with greater voltage swings to achieve maximum output
power. Fortunately, many signal sources such as audio
CODECs have outputs of 1V
RMS (2.83VP-P). Please refer to
the Audio Power Amplifier Design section for more infor-
mation on selecting the proper gain.
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitors (C1–4) in Figures 1, 3. A high value
capacitor can be expensive and may compromise space
efficiency in portable designs. In many cases, however, the
speakers used in portable systems, whether internal or ex-
ternal, have little ability to reproduce signals below 150 Hz.
Applications using speakers with this limited frequency re-
sponse reap little improvement by using large input capaci-
tor.
Besides effecting system cost and size, C1–4 have an effect
on the LM4883’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
quiescent state. The magnitude of the pop is directly propor-
tional to the input capacitor’s size. Higher value capacitors
need more time to reach a quiescent DC voltage (usually
V
DD/2) when charged with a fixed current. The amplifier’s
output charges the input capacitor through the feedback
resistors, R2,3,7,and 8. Thus, pops can be minimized by
selecting an input capacitor value that is no higher than
necessary to meet the desired 3dB frequency.
A shown in Figure 3, the input resistors (R1,4,5, and 6) and
the input capacitors, C1–4 produce a 3dB high pass filter
cutoff frequency that is found using Equation (7).
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, C
1, using Equation (7) is 0.053F. The .33F
C
1 shown in Figure 3 allows the LM4883 to drive high
efficiency, 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
5, the capacitor con-
nected to the BYPASS pin. Since C
5 determines how fast the
LM4883 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4883’s
outputs ramp to their quiescent DC voltage (nominally 1/2
V
DD), the smaller the turn-on pop. Choosing C5 equal to
1.0 F along with a small value of C
1 (in the range of 0.1 F
to 0.39 F), produces a click-less and pop-less shutdown
function. As discussed above, choosing C
1 no larger than
necessary for the desired bandwith helps minimize clicks
and pops.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4883 contains circuitry that minimizes turn-on and
shutdown transients or “clicks and pop”. For this discussion,
turn-on refers 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 LM4883’s internal
amplifiers are configured as unity gain buffers. An internal
20088724
FIGURE 4. Headphone Circuit
LM4883
www.national.com
17
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相關代理商/技術參數(shù) |
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| LM4883SQX/NOPB | 功能描述:IC AMP AUDIO PWR 3W STER 24LLP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)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(shù)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) |
| LM4884 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:2.1W Differential Input, BTL Output Stereo Audio Amplifier with RF Suppression and Shutdown |
| LM4884A E WAF | 制造商:Texas Instruments 功能描述: |
| LM4884MH | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:2.1W Differential Input, BTL Output Stereo Audio Amplifier with RF Suppression and Shutdown |
| LM4884MH/NOPB | 功能描述:IC AMP AUDIO 2.6W STER 20TSSOP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)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(shù)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) |
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