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參數(shù)資料
| 型號： | LM4841LQ/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻控制 |
| 英文描述： | 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, QCC28 |
| 封裝： | LLP-28 |
| 文件頁數(shù)： | 9/31頁 |
| 文件大小： | 1138K |
| 代理商： | LM4841LQ/NOPB |
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Application Information (Continued)
SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the LM4841’s performance requires properly se-
lecting external components. Though the LM4841 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
The LM4841 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 circuits demand 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
information on selecting the proper gain.
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires a high
value input coupling capacitor (0.33F in Figure 2), but high
value capacitors can be expensive and may compromise
space efficiency in portable designs. In many cases, how-
ever, the speakers used in portable systems, whether inter-
nal or external, have little ability to reproduce signals below
150 Hz. Applications using speakers with this limited fre-
quency response reap little improvement by using a large
input capacitor.
Besides effecting system cost and size, the input coupling
capacitor has an affect on the LM4841’s click and pop per-
formance. When the supply voltage is first applied, a tran-
sient (pop) is created as the charge on the input capacitor
changes from zero to a quiescent 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
DD/2) when charged with a fixed cur-
rent. The amplifier’s output charges the input capacitor
through the feedback resistor, R
f. Thus, pops can be mini-
mized by selecting an input capacitor value that is no higher
than necessary to meet the desired 6dB frequency.
As shown in Figure 2, the input resistor (R
IA,RIB = 20k) ( and
the input capacitor (C
IA,CIB = 0.33F) produce a 6dB 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, the input coupling capacitor, using Equation
(7), is 0.063F. The 0.33F input coupling capacitor shown
in Figure 2 allows the LM4841 to drive a high efficiency, full
range speaker whose response extends below 30Hz.
TURN ON Characteristics
The LM4841 contains advanced circuitry that minimizes
turn-on and shutdown transients or “clicks and pops”. 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
LM4841’s internal amplifiers are configured as unity gain
buffers. 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 amplifiers remains unity until the
voltage on the BYPASS pin reaches 1/2 V
DD. As soon as the
voltage on the BYPASS pin is stable, the LM4841 is ready to
be fully turned on. To turn the device on, the input signal
must exceed 22mV
rms.
This is accomplished through a
threshold detect circuit that enables all appropriate output
amplifiers after the 22mVrms limit is reached. Until this
threshold is reached, some of the amplifiers remain in a
tri-state mode. This insures that there is no current flowing
through to the speakers or headphones during power up.
Without current flow, the speakers or headphones remain
silent. During headphone mode, A+, B-, and B+ are in tri-
state mode during power up. During speaker mode, A+ and
B+ are in tri-state mode during power up.
Although the BYPASS pin current cannot be modified,
changing the size of C
BYP alters the device’s turn-on time. As
the size of C
BYP increases, the turn-on time increases. There
is a linear relationship between the size of C
BYP and the
turn-on time. Here are some typical turn-on times for various
values of C
BYP:
C
BYP
T
ON
0.01F
2ms
0.1F
20ms
0.22F
44ms
0.47F
94ms
1.0F
200ms
DOCKING STATION INTERFACE
Applications such as notebook computers can take advan-
tage of a docking station to connect to external devices such
as monitors or audio/visual equipment that sends or receives
line level signals. The LM4841 has two outputs, Dock A and
Dock B, which connect to outputs of the internal input am-
plifiers that drive the volume control inputs. These input
amplifiers can drive loads of >1k
(such as powered speak-
ers) with a rail-to-rail signal. Since the output signal present
on the Dock A and Dock B pins are biased to V
DD/2, coupling
capacitors should be connected in series with the load when
using these outputs. Typical values for the output coupling
capacitors are 0.33F to 1.0F. If polarized coupling capaci-
tors are used, connect their ’+’ terminals to the respective
output pin.
Since the Dock outputs precede the internal volume control,
the signal amplitude will be equal to the input signal’s mag-
nitude and cannot be adjusted. However, the input amplifi-
er’s closed-loop gain can be adjusted using external resis-
tors. These 20k resistors (R
2 and they set each input amplifier’s gain to -1. Use Equation
7 to determine the input and feedback resistor values for a
desired gain.
-A
v =RF /RIN
(8)
Adjusting the input amplifier’s gain sets the minimum gain for
that channel. Although the single ended output of the Bridge
Output Amplifiers can be used to drive line level outputs, it is
recommended that the A & B Dock Outputs simpler signal
path be used for better performance.
LM4841
www.national.com
17
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相關代理商/技術參數(shù) |
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|---|---|
| LM4841MH | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 2W Amplifiers with DC Volume Control, Transient Free Outputs, and Cap-less Headphone Drive |
| LM4841MH/NOPB | 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP 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) |
| LM4841MT | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 2W Amplifiers with DC Volume Control, Transient Free Outputs, and Cap-less Headphone Drive |
| LM4841MT/NOPB | 功能描述:IC AMP AUDIO PWR 2.2W AB 28TSSOP 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) |
| LM4842 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 2W Amplifiers with DC Volume Control Transient Free Outputs, and Cap-less Headphone Drive |
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