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參數(shù)資料
| 型號(hào)： | LM4868MT/NOPB |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 1.5 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO20 |
| 封裝： | 4.40 MM, PLASTIC, TSSOP-20 |
| 文件頁數(shù)： | 9/28頁 |
| 文件大?。?/td> | 792K |
| 代理商： | LM4868MT/NOPB |
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Application Information (Continued)
Single-Ended Output Power Performance and
Measurement Considerations
The LM4868 delivers clean, low distortion SE output power
into loads that are greater than 10
. As an example, output
power for 16
and 32 loads are shown in the Typical
Performance Characteristic curves. For loads less than
10
, the LM4876 can typically supply 180mW of low distor-
tion power. However, when higher dissipation is desired in
loads less than 10
, a dramatic increase in THD+N may
occur. This is normal operation and does not indicate that
proper functionality has ceased. When a jump from moder-
ate to excessively high distortion is seen, simply reducing
the output voltage swing will restore the clean, low distortion
SE operation.
The dramatic jump in distortion for loads less than 10
occurs when current limiting circuitry activates. During SE
operation, AMP2A (refer to Figure 4) drives the headphone
sleeve. An on-board circuit monitors this amplifier’s output
current. The sudden increase in THD+N is caused by the
current limit circuitry forcing AMP2A into a highimpedance
output mode. When this occurs, the output waveform has
discontinuities that produce large amounts of distortion. It
has been observed that as the output power is steadily
increased, the distortion may jump from 5% to greater than
35%. Indeed, 10% THD+N may not actually be achievable.
Using the SingleEnded Output for Line Level
Applications
Some samples of the LM4868 may exhibit small amplitude,
high frequency oscillation when the SE output is connected
to a line-level input. This oscillation can be eliminated by
connecting a 5%, 300
resistor between Amp2A’s output pin
and each amplifier, AMP1A and AMP1B, output.
SELECTING EXTERNAL COMPONENTS
Input Capacitor Value Selection
Amplifying the lowest audio frequencies requires high value
input coupling capacitor (C
i in Figure 4). A high value capaci-
tor can be expensive and may compromise space efficiency
in portable designs. In many cases, however, the speakers
used in portable systems, whether internal or external, have
little ability to reproduce signals below 150Hz. Applications
using speakers with this limited frequency response reap
little improvement by using large input capacitor.
Besides effecting system cost and size, C
i has an affect on
the LM4868’s click and pop performance. When the supply
voltage is first applied, a transient (pop) is created as the
charge on the input capacitor changes from zero to a quies-
cent 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 (usually V
DD/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 selecting an input
capacitor value that is no higher than necessary to meet the
desired 3dB frequency and is between 0.14C
B and 0.20CB.
A shown in Figure 4, the input resistor (R
I) and the input
capacitor, C
I produce a 3dB high pass filter cutoff frequency
that is found using Equation (7).
f
3dB = 1/(2
πR
INCI)
(7)
As an example when using a speaker with a low frequency
limit of 150Hz, C
i, using Equation (4) is 0.063F. The 1.0F
C
i shown in Figure 4 allows the LM4868 to drive high effi-
ciency, full range speaker whose response extends below
30Hz.
Bypass Capacitor Value Selection
Besides minimizing the input capacitor size, careful consid-
eration should be paid to value of C
B, the capacitor con-
nected to the BYPASS pin. Since C
B determines how fast
the LM4868 settles to quiescent operation, its value is critical
when minimizing turn-on pops. The slower the LM4868’s
outputs ramp to their quiescent DC voltage (nominally 1/2
200267A1
FIGURE 7. The PCDN042 provides additional ESD
protection beyond the 8000V shown in the Absolute
Maximum Ratings for the AMP2A output
20026724
FIGURE 8. Headphone Circuit
(Pin numbers in ( ) are for the 20-pin MTE and MT
packages.)
LM4868
www.national.com
17
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| 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 |
| LM4869MHX/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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