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參數(shù)資料
| 型號： | LM4868MTEX/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 3 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
| 封裝： | 6.50 X 4.40 MM, 0.90 MM HEIGHT, EXPOSED PAD, PLASTIC, TSSOP-20 |
| 文件頁數(shù)： | 10/28頁 |
| 文件大小： | 792K |
| 代理商： | LM4868MTEX/NOPB |
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Application Information (Continued)
V
DD), the smaller the turn-on pop. Choosing CB equal to
1.0F along with a small value of C
i (in the range of 0.1F to
0.39F), produces a click-less and pop-less shutdown func-
tion. As discussed above, choosing C
i no larger than neces-
sary for the desired bandwidth helps minimize clicks and
pops. C
B’s value should be in the range of 5 times to 7 times
the value of C
i. This ensures that output transients are
eliminated when power is first applied or the LM4868 re-
sumes operation after shutdown.
OPTIMIZING CLICK AND POP REDUCTION
PERFORMANCE
The LM4868 contains circuitry that eliminates turn-on and
shutdown transients (“clicks and pops“) and transients that
could occur when switching between BTL speakers and
single-ended headphones. For this discussion, turn-on re-
fers 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 LM4868’s internal amplifiers
are configured as unity gain buffers and are disconnected
from the -OUT and +OUT pins. 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 amplifi-
ers 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 and the amplifier out-
puts are reconnected to the -OUT and +OUT pins. Although
the BYPASS pin current cannot be modified, changing the
size of C
B alters the device’s turn-on time. There is a linear
relationship between the size of C
B and the turn-on time.
Here are some typical turn-on times for various values of C
B:
C
B
T
ON
0.01F
3ms
0.1F
30ms
0.22F
63ms
0.47F
134ms
1.0F
300ms
2.2F
630ms
In order eliminate “clicks and pops“, all capacitors must be
discharged before turn-on. Rapidly switching V
DD may not
allow the capacitors to fully discharge, which may cause
“clicks and pops“.
NO LOAD STABILITY
The LM4868 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:
1 W
RMS
Load Impedance:
8
Input Level:
1 V
RMS
Input Impedance:
20 k
Bandwidth:
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+(VODTOP +VODBOT))
(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
LM4868 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 LM4868’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 LM4868’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
i) and
feedback (R
i) resistors. With the desired input impedance
set at 20k
, the feedback resistor is found using Equation
(11).
R
f/Ri =AVD/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
LM4868
www.national.com
18
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM4868MT/NOPB | 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
| LM4868MTX/NOPB | 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
| LM4868LQ/NOPB | 3 W, 2 CHANNEL, AUDIO AMPLIFIER, PQCC24 |
| LM4868LQX/NOPB | 3 W, 2 CHANNEL, AUDIO AMPLIFIER, PQCC24 |
| LM4869MH/NOPB | 2.6 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4869 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1.9W Differential Input, BTL Output Stereo Audio Amplifier with Selectable Gain and Shutdown |
| LM4869MH | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1.9W Differential Input, BTL Output Stereo Audio Amplifier with Selectable Gain and Shutdown |
| LM4869MH/NOPB | 功能描述:IC AMP AUDIO PWR 2.6W AB 20TSSOP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標(biāo)準(zhǔn)包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機(jī)，2-通道（立體聲） 在某負(fù)載時(shí)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(diǎn):I²C，麥克風(fēng)，靜音，短路保護(hù)，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4870 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1.1W Audio Power Amplifier with Shutdown Mode |
| LM4870M | 制造商:Rochester Electronics LLC 功能描述:- Bulk |
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