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參數(shù)資料
| 型號： | LM4831 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Multimedia Computer Audio Chip |
| 中文描述： | 多媒體計算機音頻芯片 |
| 文件頁數(shù)： | 11/12頁 |
| 文件大小： | 575K |
| 代理商： | LM4831 |
Application Information
(Continued)
ducing Cb will decrease turn-on time and increase “click and
pop”. If Cb is too small, the LM4831 can develop a
low-frequency oscillation (“motorboat”) when used at high
gains.
In order to eliminate “click and pop”, all coupling capacitors
must be discharged before turn-on. Rapid on/off switching of
the device or shutdown function may cause the “click and
pop” circuitry to not operate fully, resulting in increased “click
and pop” noise. For single-ended (headphone) circuitry, the
output coupling cap, C
, is of particular concern. In shut-
down, this capacitor is discharged through an internal 20k
resistor. Depending on the size of C
, the discharging time
constant can be quite large. To reduce the time constant, an
external 1k
-5k
resistor can be placed in parallel with the
internal 20k
resistor. The tradeoff for using this resistor is
an increase in quiescent current and an increase in turn-off
“click and pop”.
Changing the bypass capacitor size also affects the amount
of time that the beep circuitry turns on the LM4831. Increas-
ing the bypass capacitor size increases the turn-on time,
which reduces the amount of time that the LM4831 is fully on
for during the RC-timed beep period.
The bypass capacitor also helps determine the power supply
rejection ratio. The smaller the bypass capacitor, the more
the power supply ripples couple onto the half supply and
then to all circuitry which uses the half supply for biasing.
COUPLING CAPACITORS
Since the LM4831 is a single supply circuit, all audio signals
(excepting the bridged outputs) must be capacitor coupled to
the chip to remove the 2.5V
bias. All audio inputs have a
20k
input impedance, so theAC-coupling capacitor will cre-
ate a high-pass filter with f
= 1/(2
π
*20k
*C
in
). For a
3dB point at 20Hz, C
in
should be 0.39μF
Single-ended and line-out loads need to beAC-coupled back
to the LM4831 amplifiers. This high-pass filter is comprised
of the output load and the coupling capacitor, where the filter
cutoff is at f
= 1/(2
π
*R
*C
). If R
=8
, then for a
3dB point at 20Hz, C
out
should be 1000μF.
EQUALIZER INPUT/OUTPUT
In some systems, the internal speakers require filtering to
improve their frequency response. The LM4831 provides the
system designer with external access to the signal using the
equalizer output and equalizer inputpins. When the DS_IN
and HP_IN pins are low (ie. the system is not in the docking
station and no headphone are plugged in), an internal mux
routes the audio signal to the equalizer output pin. After the
signal is filtered, it is returned to the LM4831 audio path
through the equalizer inputpin.
The input impedance to the equalizer input pin is 20k
. If the
external filter’s bias voltage is not derived from the half sup-
ply pin on the LM4831,AC-coupling capacitors must be used
on the equalizer input and output pins. If no equalization is
required, the equalizer out pin can be connected directly to
the equalizer in pin without any coupling capacitors.
LINE OUT
The line out pins are designed for use with a docking station
system. When the computer is plugged into the docking sta-
tion, the DS_IN pin should be forced high, thereby turning off
the power amplifier outputs and turning on the line out ampli-
fiers. All audio amplification and filtering is then done by the
docking station. The line out pins must be AC-coupled to the
docking station audio inputs.
POWER AMPLIFIERS
The power amplifiers in the LM4831 are designed to drive
8
or 32
loads at 1W (continuous) or 250mW(continuous),
respectively, with 1% THD+N. If the power amplifiers are
used to drive single-ended loads, such as headphones, the
amplifier inverting outputs should be AC-coupled to the out-
put load. When the LM4831 is in headphone (single-ended)
mode, the amplifier non-inverting inputs are in a high-
impedance state.
In low gain applications (A
<
5), the LM4831 may require a
small feedback capacitance to prevent oscillation. Typically,
5-10pF will prevent oscillation.
MICROPHONE AMPLIFIER
The microphone amplifier is an uncommitted op-amp which
is intended to amplify low-level signals. The microphone in-
puts are very high impedance (R
>
1M
) and can be di-
rectly connected to microphone networks. The microphone
amplifier has enough output capability to drive a 1k
load.
All microphone inputs and outputs must be AC-coupled.
As shown in Figure 1 the microphone amplifier is typically
configured as an inverting amplifier. The positive terminal is
connected to the half-supply bypass pin to properly bias the
amplifier output to interface with the other inputs on the
LM4831. The microphone input pin is connected to the in-
verting node of a CMOS op amp, so the input impedance is
very high (
>
10M
)
BEEP CIRCUITRY
The beep circuitry is designed to allow a “sleeping” system to
temporarily power-up the LM4831 and output an audio alert
(“beep”). This feature might be used in a computer which is
“sleeping”, but needs to notify the user that the computer
batteries are low or that the user has new e-mail.
The beep circuitry is activated by any edge which occurs on
the BEEP A-D pins. With a resistor, R
, and a capacitor,
C
, in parallel at the RC pin of the LM4831, the LM4831
will be activated for R
C
seconds. Typical values for
R
beep
and R
beep
are 1-10
M and 0.1μF.
The BEEP OUT pin is designed to signal other audio circuitry
that the LM4831 is powering up. Generally a CODEC will re-
ceive this signal and begin sending audio information to the
LM4831. Logically, the BEEP OUT signal is the result of an
XOR of the BEEP A-D pins.
www.national.com
11
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4831 WAF | 制造商:Texas Instruments 功能描述: |
| LM48310 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Ultra-Low EMI, Filterless, 2.6W, Mono, Class D Audio Power Amplifier with E2S |
| LM48310SD | 制造商:Texas Instruments 功能描述:Audio Amp Speaker 1-CH Mono 2.6W Class-D 10-Pin LLP EP T/R |
| LM48310SD/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(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM48310SDBD | 功能描述:音頻 IC 開發(fā)工具 LM48310SD EVAL BOARD RoHS:否 制造商:Texas Instruments 產(chǎn)品:Evaluation Kits 類型:Audio Amplifiers 工具用于評估:TAS5614L 工作電源電壓:12 V to 38 V |
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