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參數(shù)資料
| 型號(hào)： | LM4911MM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | Stereo 40mW Low Noise Headphone Amplifier with Selectable Capacitive Coupled or OCL Output |
| 中文描述： | 0.145 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 |
| 封裝： | MSOP-10 |
| 文件頁數(shù)： | 15/18頁 |
| 文件大小： | 923K |
| 代理商： | LM4911MM |
Application Information
AMPLIFIER CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4911 has three operational
amplifiers internally. Two of the amplifier’s have externally
configurable gain while the other amplifier is internally fixed
at the bias point acting as a unity-gain buffer. The closed-
loop gain of the two configurable amplifiers is set by select-
ing the ratio of R
f
to R
i
. Consequently, the gain for each
channel of the IC is
A
VD
= -(R
f
/ R
i
)
By driving the loads through outputs V
A and V
B with V
C
acting as a buffered bias voltage the LM4911 does not
require output coupling capacitors. The classical single-
ended amplifier configuration where one side of the load is
connected to ground requires large, expensive output cou-
pling capacitors.
A configuration, such as the one used in the LM4911, has a
major advantage over single supply, single-ended amplifiers.
Since the outputs V
A, V
B, and V
V
, no net DC voltage exists across each load. This elimi-
nates the need for output coupling capacitors which are
required in a single-supply, single-ended amplifier configura-
tion. Without output coupling capacitors in a typical single-
supply, single-ended amplifier, the bias voltage is placed
across the load resulting in both increased internal IC power
dissipation and possible loudspeaker damage.
OUTPUT CAPACITOR vs. CAPACITOR COUPLED
The LM4911 is a stereo audio power amplifier capable of
operating in two distinct output modes: capacitor coupled
(C-CUPL) or output capacitor-less (OCL). The LM4911 may
be run in capacitor coupled mode by using a coupling ca-
pacitor on each single-ended output (V
o
A and V
o
B) and
connecting V
o
C to ground. This output coupling capacitor
blocks the half supply voltage to which the output amplifiers
are typically biased and couples the audio signal to the
headphones or other single-ended (SE) load. The signal
return to circuit ground is through the headphone jack’s
sleeve.
The LM4911 can also eliminate these output coupling ca-
pacitors by running in OCL mode. Unless shorted to ground,
VoC is internally configured to apply a
1
2
Vdd bias voltage to
a stereo headphone jack’s sleeve. This voltage matches the
bias voltage present on V
A and V
B outputs that drive the
headphones. The headphones operate in a manner similar
to a bridge-tied load (BTL). Because the same DC voltage is
applied to both headphone speaker terminals this results in
no net DC current flow through the speaker.AC current flows
through a headphone speaker as an audio signal’s output
amplitude increases on the speaker’s terminal.
The headphone jack’s sleeve is not connected to circuit
ground when used in OCL mode. Using the headphone
output jack as a line-level output will place the LM4911’s
1
2
V
bias voltage on a plug’s sleeve connection. This pre-
sents no difficulty when the external equipment uses capaci-
tively coupled inputs. For the very small minority of equip-
ment that is DC coupled, the LM4911 monitors the current
supplied by the amplifier that drives the headphone jack’s
sleeve. If this current exceeds 500mAPK, the amplifier is
shutdown, protecting the LM4911 and the external equip-
ment.
POWER DISSIPATION
Power dissipation is a major concern when using any power
amplifier and must be thoroughly understood to ensure a
successful design. When operating in capacitor-coupled
mode, Equation 1 states the maximum power dissipation
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
)
(1)
Since the LM4911 has two operational amplifiers in one
package, the maximum internal power dissipation point is
twice that of the number which results from Equation 1. From
Equation 1, assuming a 3V power supply and an 32
load,
the maximum power dissipation point is 14mW per amplifier.
Thus the maximum package dissipation point is 28mW.
When operating in OCL mode, the maximum power dissipa-
tion increases due to the use of the third amplifier as a buffer
and is given in Equation 2:
P
DMAX
= 4(V
DD
)
2
/ (
π
2
R
L
)
(2)
The maximum power dissipation point obtained from either
Equation 1 or 2 must not be greater than the power dissipa-
tion that results from Equation 3:
P
DMAX
= (T
JMAX
- T
A
) /
θ
JA
(3)
For package MUB10A,
θ
JA
= 190C/W. T
JMAX
= 150C for
the LM4911. Depending on the ambient temperature, T
A
, 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 1 or 2 is greater than that
of Equation 3, then either the supply voltage must be de-
creased, the load impedance increased or T
A
reduced. For
the typical application of a 3V power supply, with an 32
load, the maximum ambient temperature possible without
violating the maximum junction temperature is approximately
144C provided that device operation is around the maxi-
mum power dissipation point. Thus, for typical applications,
power dissipation is not an issue. Power dissipation is a
function of output power and thus, if typical operation is not
around the maximum power dissipation point, the ambient
temperature may be increased accordingly. Refer to the
Typical Performance Characteristics curves for power dissi-
pation information for lower output powers.
POWER SUPPLY BYPASSING
As with any amplifier, proper supply bypassing is important
for low noise performance and high power supply rejection.
The capacitor location on the power supply pins should be
as close to the device as possible.
Typical applications employ a 3V regulator with 10mF tanta-
lum or electrolytic capacitor and a ceramic bypass capacitor
which aid in supply stability. This does not eliminate the need
for bypassing the supply nodes of the LM4911. A bypass
capacitor value in the range of 0.1μF to 1μF is recommended
for C
S
.
L
www.national.com
15
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4911MM/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 |
| LM4911MMX | 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 |
| LM4911MMX/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 |
| LM4911QMM/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 |
| LM4911QMMX/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 |
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