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參數(shù)資料
| 型號： | LM4936 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Stereo 2W Audio Power Amplifiers with Volume Control and Selectable Control Interface (SPI or I2C) |
| 中文描述： | 2W的立體聲音頻功率放大器，帶有音量控制和可選控制接口（SPI或I2C） |
| 文件頁數(shù)： | 19/28頁 |
| 文件大小： | 1490K |
| 代理商： | LM4936 |
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Application Information
(Continued)
the length of leads and traces that connect capacitors be-
tween the LM4936’s power supply pin and ground as short
as possible. Connecting a 1μF capacitor, C
B
, between the
BYPASS pin and ground improves the internal bias voltage’s
stability and the amplifier’s PSRR. The PSRR improvements
increase as the BYPASS pin capacitor value increases. Too
large a capacitor, however, increases turn-on time and can
compromise the amplifier’s click and pop performance. The
selection of bypass capacitor values, especially C
, depends
on desired PSRR requirements, click and pop performance
(as explained in the following section,
Selecting Proper
External Components
), system cost, and size constraints.
SELECTING PROPER EXTERNAL COMPONENTS
Optimizing the LM4936’s performance requires properly se-
lecting external components. Though the LM4936 operates
well when using external components with wide tolerances,
best performance is achieved by optimizing component val-
ues.
The LM4936 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
(2.83V
P-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 (0.33μF 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 affecting system cost and size, the input coupling
capacitor has an effect on the LM4936’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 (V
/2) when charged with a fixed current. The
amplifier’s output charges the input capacitor through the
feedback resistor, R
f
. Thus, pops can be minimized by se-
lecting an input capacitor value that is no higher than nec-
essary to meet the desired 6dB frequency.
As shown in
Figure 2
, the input resistor (R
IR
, R
IL
= 20k
)
and the input capacitor (C
IR
, C
IL
= 0.33μF) 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 0.053μF. The 0.33μF input coupling capacitor shown
in
Figure 2
allows the LM4936 to drive a high efficiency, full
range speaker whose response extends below 30Hz.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4936 contains circuitry that minimizes turn-on and
shutdown transients or “clicks and pops”. For this discus-
sion, turn-on refers to either applying the power supply volt-
age or when the shutdown mode is deactivated. While the
power supply is ramping to its final value, the LM4936’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
.As soon as the voltage
on the BYPASS pin is stable, the device becomes fully
operational. Although the BYPASS pin current cannot be
modified, changing the size of C
alters the device’s turn-on
time and the magnitude of “clicks and pops”. Increasing the
value of C
reduces the magnitude of turn-on pops. How-
ever, this presents a tradeoff: as the size of C
increases, the
turn-on time increases. There is a linear relationship be-
tween the size of C
and the turn-on time. Below are some
typical turn-on times for various values of C
B
:
L
www.national.com
19
相關PDF資料 |
PDF描述 |
|---|---|
| LM4951 | Wide Voltage Range 1.8 Watt Audio Amplifier |
| LM4953 | Ground-Referenced, Ultra Low Noise, Ceramic Speaker Driver |
| LM4953SD | Ground-Referenced, Ultra Low Noise, Ceramic Speaker Driver |
| LM4980 | 2 Cell Battery, 1mA, 42mW Per Channel High Fidelity Stereo Headphone Audio Amplifier for MP3 players |
| LM4980SD | 2 Cell Battery, 1mA, 42mW Per Channel High Fidelity Stereo Headphone Audio Amplifier for MP3 players |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM49360 | 制造商:TI 制造商全稱:Texas Instruments 功能描述:Mono Class D Audio Codec PMU with Ground Referenced Headphone Amplifiers, Earpiece Driver, Audio DSP, 2 Step-Down DC-DC Converters, and 7 LDO Regulators |
| LM49360RL | 制造商:TI 制造商全稱:Texas Instruments 功能描述:Mono Class D Audio Codec PMU with Ground Referenced Headphone Amplifiers, Earpiece Driver, Audio DSP, 2 Step-Down DC-DC Converters, and 7 LDO Regulators |
| LM49360RLX | 制造商:TI 制造商全稱:Texas Instruments 功能描述:Mono Class D Audio Codec PMU with Ground Referenced Headphone Amplifiers, Earpiece Driver, Audio DSP, 2 Step-Down DC-DC Converters, and 7 LDO Regulators |
| LM4936MH | 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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM4936MH/NOPB | 功能描述:音頻放大器 Stereo 2W Audio Pwr Amp 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: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
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