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參數資料
| 型號： | LM4867MTE |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
| 中文描述： | 3 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
| 封裝： | 6.50 X 4.40 MM, 0.90 MM HEIGHT, EXPOSED PAD, TSSOP-20 |
| 文件頁數： | 16/26頁 |
| 文件大小： | 763K |
| 代理商： | LM4867MTE |
Application Information
(Continued)
NO LOAD STABILITY
The LM4867 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:
1 W
RMS
8
1 V
RMS
20 k
100 Hz20 kHz
±
0.25 dB
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 is
Equation (9).
(8)
V
DD
≥
(V
OUTPEAK
+ (V
OD
TOP
+ V
OD
BOT
))
(9)
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
LM4867 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
of maximum power dissipation as explained above in the
Power Dissipation
section.
After satisfying the LM4867’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 LM4867’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
f
/R
i
= A
VD
/2
(11)
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
(12)
and an
f
H
= 20kHz x 5 = 100kHz
(13)
As mentioned in the
Selecting Proper External Compo-
nents
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
i
≥
1/(2
π
R
i
f
L
)
(14)
The result is
1/(2
π
*
20k
*
20Hz) = 0.397μF
(15)
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 A
VD
, 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 LM4867’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.
RECOMMENDED PRINTED CIRCUIT BOARD LAYOUT
Figures 8 through 12 show the recommended four-layer PC
board layout that is optimized for the 24-pin LQ-packaged
LM4867 and associated external components. Figures 13
through 17 show the recommended two-layer PC board
layout that is optimized for the 24-pin MTE-packaged
LM4867 and associated external components. Figures 18
through 20 show the recommended two-layer PC board
layout that is optimized for the 20-pin MT-packaged LM4867
and associated external components. These circuits are de-
signed for use with an external 5V supply and 4
speakers.
These circuit boards are easy to use.Apply 5V and ground to
the board’s V
and GND pads, respectively. Connect 4
speakers between the board’s OUTA and +OUTA and
OUTB and +OUTB pads.
L
www.national.com
16
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相關代理商/技術參數 |
參數描述 |
|---|---|
| LM4867MTE/NOPB | 功能描述:IC AMP AUDIO PWR 3W AB 20TSSOP 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) |
| LM4867MTEX | 制造商:National Semiconductor Corporation 功能描述:Audio Amplifier Circuit, Dual, 20 Pin, Plastic, TSSOP |
| LM4867MTEX/NOPB | 功能描述:IC AMP AUDIO PWR 3W AB 20TSSOP 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) |
| LM4867MTX/NOPB | 功能描述:IC AMP AUDIO PWR 3W AB 20TSSOP 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) |
| LM4868 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Output-Transient-Free Dual 2.1W Audio Amplifier Plus No Coupling Capacitor Stereo Headphone Function |
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