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參數(shù)資料
| 型號： | LM4915 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Pseudo-Differential Mono Headphone Amplifier with Fixed 6dB Gain |
| 中文描述： | 偽差分單聲道耳機放大器，具有固定6dB增益 |
| 文件頁數(shù)： | 9/11頁 |
| 文件大?。?/td> | 516K |
| 代理商： | LM4915 |
Typical Performance Characteristics
(Continued)
I
SD
Distribution
V
DD
= 3V
200482F1
Application Information
DIFFERENTIAL AMPLIFIER EXPLANATION
The LM4915 is a pseudo-differential audio amplifier that
features a fixed gain of 6dB. Internally this is accomplished
by two separate sets of inverting amplifiers, each set to a
gain of 2. The LM4915 features precisely matched internal
gain-setting resistors set to R
= 20k
and R
= 40k
, thus
eliminating the need for external resistors and fixing the
differential gain at A
VD
= 6dB.
A differential amplifier works in a manner where the differ-
ence 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 LM4915 works in a
pseudo-differential manner, so DC offset normally cancelled
by a fully differential amplifier needs to be blocked by input
coupling capacitors for the LM4915 to amplify the difference
between the inputs.
The LM4915 provides what is known as a ’bridged mode’
output (bridge-tied-load, BTL). This results in output signals
at Vo1 and Vo2 that are 180 out of phase with respect to
each other. Bridged mode operation is different from the
single-ended amplifier configuration that connects the load
between the amplifier output and ground. A bridged amplifier
design has distinct advantages over the single-ended con-
figuration: it provides differential drive to the load, thus dou-
bling maximum possible output swing for a specific supply
voltage. Four times the output power is possible compared
with a single-ended amplifier under the same conditions.
This increase in attainable output power assumes that the
amplifier is not current limited or clipped. A bridged configu-
ration, such as the one used in the LM4915, also creates a
second advantage over single-ended amplifiers. Since the
differential outputs, Vo1 and Vo2 , are biased at half-supply,
no net DC voltage exists across the load. BTL configuration
eliminates the output coupling capacitor required in single-
supply, single-ended amplifier configurations. If an output
coupling capacitor is not used in a single-ended output con-
figuration, the half-supply bias across the load would result
in both increased internal IC power dissipation as well as
permanent loudspeaker damage.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifer, whether the amplifier is bridged or
single-ended. Equation 1 states the maximum power dissi-
pation point for a single-ended amplifier operating at a given
supply voltage and driving a specified output load.
P
DMAX
= (V
DD
)
2
/ (2
π
2
R
L
)
Single-Ended
(1)
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is an increase in
internal power dissipation versus a single-ended amplifier
operating at the same conditions.
P
DMAX
= 4(V
DD
)
2
/ (2
π
2
R
L
)
Bridge Mode
(2)
Since the LM4915 has bridged outputs, the maximum inter-
nal power dissipation is 4 times that of a single-ended am-
plifier.
Even with this substantial increase in power dissipation, the
LM4915 does not require additional heatsinking under most
operating conditions and output loading. From Equation 2,
assuming a 5V power supply and an 16
load, the maximum
power dissipation point is 316mW. The maximum power
dissipation point obtained from Equation 2 must not be
greater than the power dissipation results from Equation 3:
P
DMAX
= (T
JMAX
- T
A
) /
θ
JA
(3)
The LM4915’s
θ
in an LQB08A package is 140C/W. De-
pending on the ambient temperature, T
, of the system
surroundings, Equation 3 can be used to find the maximum
internal power dissipation supported by the IC packaging. If
the result of Equation 2 is greater than that of Equation 3,
L
www.national.com
9
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM49150 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Mono Class D Audio Subsystem with Earpiece Driver and Stereo Ground Referenced Headphone Amplifiers |
| LM49150TL | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Mono Class D Audio Subsystem with Earpiece Driver and Stereo Ground Referenced Headphone Amplifiers |
| LM49150TL/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM49150TLEVAL | 功能描述:音頻 IC 開發(fā)工具 LM49150TL EVAL BOARD RoHS:否 制造商:Texas Instruments 產(chǎn)品:Evaluation Kits 類型:Audio Amplifiers 工具用于評估:TAS5614L 工作電源電壓:12 V to 38 V |
| LM49150TLX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Mono Class D Audio Subsystem with Earpiece Driver and Stereo Ground Referenced Headphone Amplifiers |
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