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參數資料
| 型號： | LM4883SQ |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | Dual 2.1W Audio Amplifier Plus Stereo Headphone |
| 中文描述： | 0.4 W, 2 CHANNEL, AUDIO AMPLIFIER, QCC24 |
| 封裝： | LLP-24 |
| 文件頁數： | 18/23頁 |
| 文件大?。?/td> | 1244K |
| 代理商： | LM4883SQ |
Application Information
(Continued)
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 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. However, this
presents a tradeoff: as the size of C
increases, the turn-on
time increases. There is a linear relationship between the
size of C
and the turn-on time. Here are some typical
turn-on times for various values of C
5
:
C
5
0.01μF
0.1μF
0.22μF
0.47μF
1.0μF
T
ON
30ms
40ms
60ms
80ms
140 ms
In order eliminate “clicks and pops”, all capacitors must be
discharged before turn-on. Rapidly switching V
may not
allow the capacitors to fully discharge, which may cause
“clicks and pops”. In a single-ended configuration, the output
is coupled to the load by C7,8. These capacitors usually
have a high value. C7,8 discharges through internal 20k
resistors. Depending on the size of C7,8, the discharge time
constant can be relatively large. To reduce transients in
single-ended mode, an external 1k
–5k
resistor can be
placed in parallel with the internal 20k
resistor. The tradeoff
for using this resistor is increased quiescent current.
NO LOAD STABILITY
The LM4883 may exhibit low level oscillation when the load
resistance is greater than 10k
. This oscillation only occurs
as the output signal swings near the supply voltages. Pre-
vent this oscillation by connecting a 5k
between the output
pins and ground.
AUDIO POWER AMPLIFIER DESIGN
Audio Amplifier Design: Driving 1W into an 8
Load
The following are the desired operational parameters:
Power Output:
Load Impedance:
Input Level:
Input Impedance:
Bandwidth:
1W
RMS
8
1V
rms
20k
100Hz20kHz
±
0.25dB
The design begins by specifying the minimum supply voltage
necessary to obtain the specified output power. One way to
find the minimum supply voltage is to use the Output Power
vs Supply Voltage curve in the
Typical Performance Char-
acteristics
section. Another way, using Equation (8), is to
calculate the peak output voltage necessary to achieve the
desired output power for a given load impedance. To ac-
count for the amplifier’s dropout voltage, two additional volt-
ages, based on the Dropout Voltage vs Supply Voltage in the
Typical Performance Characteristics
curves, must be
added to the result obtained by Equation (8). The result in
Equation (9).
(8)
(9)
V
DD
≥
(V
OUTPEAK
+ (V
OD
TOP
+ V
OD
BOT
))
The Output Power vs Supply Voltage graph for an 8
load
indicates a minimum supply voltage of 4.6V. This is easily
met by the commonly used 5V supply voltage. The additional
voltage creates the benefit of headroom, allowing the
LM4883 to produce peak output power in excess of 1W
without clipping or other audible distortion. The choice of
supply voltage must also not create a situation that violates
maximum power dissipation as explained above in the
Power Dissipation
section.
After satisfying the LM4883’s power dissipation require-
ments, the minimum differential gain needed to achieve 1W
dissipation in an 8
load is found using Equation (10).
(10)
Thus, a minimum gain of 2.83 allows the LM4883’s to reach
full output swing and maintain low noise and THD+N perfor-
mance. For this example, let A
VD
= 3.
The amplifier’s overall gain is set using the input (R
) and
feedback (R
) resistors. With the desired input impedance
set at 20k
, the feedback resistor is found using Equation
(11).
R
3
/R
1
= A
VD
/2
The value of R
f
is 30k
.
The last step in this design example is setting the amplifier’s
3dB frequency bandwidth. To achieve the desired
±
0.25dB
pass band magnitude variation limit, the low frequency re-
sponse must extend to at least one-fifth the lower bandwidth
limit and the high frequency response must extend to at least
five times the upper bandwidth limit. The gain variation for
both response limits is 0.17dB, well within the
±
0.25dB
desired limit. The results are an
f
L
= 100Hz/5 = 20Hz
and an
f
H
= 20kHz*5 = 100kHz.
As mentioned in the
External Components
section, R
and
C
create a highpass filter that sets the amplifier’s lower
bandpass frequency limit. Find the coupling capacitor’s
value using Equation (12).
C
1
≥
1/(2
π
R
1
f
L
)
The result is
1/(2
π
*20k
*20Hz) = 0.398μF.
Use a 0.39μF capacitor, the closest standard value.
The product of the desired high frequency cutoff (100kHz in
this example) and the differential gain, AVD, determines the
upper passband response limit. With A
= 3 and f
=
100kHz, the closed-loop gain bandwidth product (GBWP) is
300kHz. This is less than the LM4883’s 3.5MHz GBWP. With
this margin, the amplifier can be used in designs that require
more differential gain while avoiding performance-restricting
bandwidth limitations.
(11)
(12)
L
www.national.com
18
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LM4883SQ/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) |
| LM4883-SQ_BOM-001A | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Demo Board |
| 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: |
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