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參數(shù)資料
| 型號： | LM4894MWC |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 1 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC |
| 封裝： | WAFER |
| 文件頁數(shù)： | 5/21頁 |
| 文件大?。?/td> | 781K |
| 代理商： | LM4894MWC |
Application Information (Continued)
used, but PSRR decreases at frequencies below 1kHz. The
issue of C
B selection is thus dependant upon desired PSRR
and click and pop performance as explained in the section
Proper Selection of External Components.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4894 contains shutdown circuitry that is used to turn off
the amplifier’s bias circuitry. In addition, the LM4894 con-
tains a Shutdown Mode pin, allowing the designer to desig-
nate whether the part will be driven into shutdown with a high
level logic signal or a low level logic signal. This allows the
designer maximum flexibility in device use, as the Shutdown
Mode pin may simply be tied permanently to either V
DD or
GND to set the LM4894 as either a ’shutdown-high’ device or
a ’shutdown-low’ device, respectively. The device may then
be placed into shutdown mode by toggling the Shutdown
Select pin to the same state as the Shutdown Mode pin. For
simplicity’s sake, this is called ’shutdown same’, as the
LM4894 enters shutdown mode whenever the two pins are
in the same logic state. The trigger point for either shutdown
high or shutdown low is shown as a typical value in the
Supply Current vs Shutdown Voltage graphs in the Typical
Performance Characteristics section. It is best to switch
between ground and supply for maximum performance.
While the device may be disabled with shutdown voltages in
between ground and supply, the idle current may be greater
than the typical value of 0.1A. In either case, the shutdown
pin should be tied to a definite voltage to avoid unwanted
state changes.
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry, which pro-
vides a quick, smooth transition to shutdown. Another solu-
tion is to use a single-throw switch in conjunction with an
external pull-up resistor (or pull-down, depending on shut-
down high or low application). This scheme guarantees that
the shutdown pin will not float, thus preventing unwanted
state changes.
PROPER SELECTION OF EXTERNAL COMPONENTS
Proper selection of external components in applications us-
ing integrated power amplifiers is critical when optimizing
device and system performance. Although the LM4894 is
tolerant to a variety of external component combinations,
consideration of component values must be made when
maximizing overall system quality.
The LM4894 is unity-gain stable, giving the designer maxi-
mum system flexibility. The LM4894 should be used in low
closed-loop gain configurations to minimize THD+N values
and maximize signal to noise ratio. Low gain configurations
require large input signals to obtain a given output power.
Input signals equal to or greater than 1Vrms are available
from sources such as audio codecs. Please refer to the
Audio Power Amplifier Design section for a more complete
explanation of proper gain selection. When used in its typical
application as a fully differential power amplifier the LM4894
does not require input coupling capacitors for input sources
with DC common-mode voltages of less than VDD. Exact
allowable input common-mode voltage levels are actually a
function of V
DD,Ri, and Rf and may be determined by
Equation 5:
V
CMi<(VDD-1.2)*((Rf+(Ri)/(Rf)-VDD*(Ri/2Rf)
(5)
V
CMi<(VDD-1.2)*((Rf+(Ri)/(Rf)-VDD*(Ri/2Rf)
(6)
Special care must be taken to match the values of the
feedback resistors (R
F1 and RF2) to each other as well as
matching the input resistors (R
i1 and Ri2) to each other (see
Figure 1) more infront. Because of the balanced nature of
differential amplifiers, resistor matching differences can re-
sult in net DC currents across the load. This DC current can
increase power consumption, internal IC power dissipation,
reduce PSRR, and possibly damaging the loudspeaker. The
chart below demonstrates this problem by showing the ef-
fects of differing values between the feedback resistors while
assuming that the input resistors are perfectly matched. The
results below apply to the application circuit shown in Figure
1, and assumes that V
DD =5V, RL =8
, and the system has
DC coupled inputs tied to ground.
Tolerance R
F1
R
F2
V
02 -V01
I
LOAD
20%
0.8R
1.2R
-0.500V
62.5mA
10%
0.9R
1.1R
-0.250V
31.25mA
5%
0.95R 1.05R -0.125V
15.63mA
1%
0.99R 1.01R -0.025V
3.125mA
0%
RR0
0
Similar results would occur if the input resistors were not
carefully matched. Adding input coupling capacitors in be-
tween the signal source and the input resistors will eliminate
this problem, however, to achieve best performance with
minimum component count it is highly recommended that
both the feedback and input resistors matched to 1% toler-
ance or better.
AUDIO POWER AMPLIFIER DESIGN
Design a 1W/8
Audio Amplifier
Given:
Power Output
1Wrms
Load Impedance
8
Input Level
1Vrms
Input Impedance
20k
Bandwidth
–20kHz ± 0.25dB
A designer must first determine the minimum supply rail to
obtain the specified output power. The supply rail can easily
be found by extrapolating from the Output Power vs Supply
Voltage graphs in the Typical Performance Characteris-
tics section. A second way to determine the minimum supply
rail is to calculate the required VOPEAK using Equation 7
and add the dropout voltages. Using this method, the mini-
mum supply voltage is (Vopeak +(V
DO TOP+(VDO BOT )),
where V
DO BOT and VDO TOP are extrapolated from the
Dropout Voltage vs Supply Voltage curve in the Typical
Performance Characteristics section.
(7)
Using the Output Power vs Supply Voltage graph for an 8W
load, the minimum supply rail just about 5V. Extra supply
voltage creates headroom that allows the LM4894 to repro-
LM4894
www.national.com
13
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4895 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1 Watt Fully Differential Audio Power Amplifier With Shutdown Select and Fixed 6dB Gain |
| LM4895A E WAF | 制造商:Texas Instruments 功能描述: |
| LM4895IBP | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1 Watt Fully Differential Audio Power Amplifier With Shutdown Select and Fixed 6dB Gain |
| LM4895IBP/NOPB | 功能描述:IC AMP AUDIO PWR 1.4W MONO 9USMD 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) |
| LM4895IBPX | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
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