参数资料
型号: LM4894LD/NOPB
厂商: NATIONAL SEMICONDUCTOR CORP
元件分类: 音频/视频放大
英文描述: 1.4 W, 1 CHANNEL, AUDIO AMPLIFIER, DSO10
封装: LLP-10
文件页数: 3/19页
文件大小: 770K
代理商: LM4894LD/NOPB
Typical Performance Characteristics
Non-LD Specific Characteristics (Continued)
PSRR vs
DC Common-Mode Voltage
PSRR vs
DC Common-Mode Voltage
20013780
20013781
THD vs
Common-Mode Voltage
THD vs
Common-Mode Voltage
20013782
20013783
Application Information
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM4894 is a fully differential audio amplifier that fea-
tures differential input and output stages. Internally this is
accomplished by two circuits: a differential amplifier and a
common mode feedback amplifier that adjusts the output
voltages so that the average value remains V
DD/2. When
setting the differential gain, the amplifier can be considered
to have "halves". Each half uses an input and feedback
resistor (R
i1and RF1) to set its respective closed-loop gain
(see Figure 1). With R
i1 =Ri2 and RF1 =RF2, the gain is set
at -R
F/Ri for each half. This results in a differential gain of
A
VD =-RF/Ri
(1)
It is extremely important to match the input resistors to each
other, as well as the feedback resistors to each other for best
amplifier performance. See the Proper Selection of Exter-
nal Components section for more information. A differential
amplifier works in a manner where the difference between
the two input signals is amplified. In most applications, this
would require input signals that are 180 out of phase with
each other. The LM4894 can be used, however, as a single
ended input amplifier while still retaining its fully differential
benefits. In fact, completely unrelated signals may be placed
on the input pins. The LM4894 simply amplifies the differ-
ence between them. Figures 2 and 3 show single-ended
applications of the LM4894 that still take advantage of the
differential nature of the amplifier and the benefits to PSRR,
common-mode noise reduction, and "click and pop" reduc-
tion.
All of these applications, either single-ended or fully differ-
ential, provide what is known as a "bridged mode" output
(bridge-tied-load, BTL). This results in output signals at V
o1
and V
o2 that are 180 out of phase with respect to each
LM4894
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相关代理商/技术参数
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