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參數(shù)資料
| 型號： | LM4917SD |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | Ground-Referenced, 95mW Stereo Headphone Amplifier |
| 中文描述： | 0.095 W, 2 CHANNEL, AUDIO AMPLIFIER, DSO14 |
| 封裝： | LLP-14 |
| 文件頁數(shù)： | 11/18頁 |
| 文件大?。?/td> | 1208K |
| 代理商： | LM4917SD |
Application Information
ELIMINATING THE OUTPUT COUPLING CAPACITOR
The LM4917 features a low noise inverting charge pump that
generates an internal negative supply voltage. This allows
the outputs of the LM4917 to be biased about GND instead
of a nominal DC voltage, like traditional headphone amplifi-
ers. Because there is no DC component, the large DC
blocking capacitors (typically 220μF) are not necessary. The
coupling capacitors are replaced by two, small ceramic
charge pump capacitors, saving board space and cost.
Eliminating the output coupling capacitors also improves low
frequency response. The headphone impedance and the
output capacitor form a high pass filter that not only blocks
the DC component of the output, but also attenuates low
frequencies, impacting the bass response. Because the
LM4917 does not require the output coupling capacitors, the
low frequency response of the device is not degraded by
external components.
In addition to eliminating the output coupling capacitors, the
ground referenced output nearly doubles the available dy-
namic range of the LM4917 when compared to a traditional
headphone amplifier operating from the same supply volt-
age.
OUTPUT TRANSIENT (’CLICK AND POPS’)
ELIMINATED
The LM4917 contains advanced circuitry that virtually elimi-
nates output transients (’clicks and pops’). This circuitry
prevents all traces of transients when the supply voltage is
first applied or when the part resumes operation after coming
out of shutdown mode.
To ensure optimal click and pop performance under low gain
configurations (less than 0dB), it is critical to minimize the
RC combination of the feedback resistor R
F
and stray input
capacitance at the amplifier inputs. A more reliable way to
lower gain or reduce power delivered to the load is to place
a current limiting resistor in series with the load as explained
in the
Minimizing Output Noise / Reducing Output Power
section.
AMPLIFIER CONFIGURATION EXPLANATION
As shown in Figure 2, the LM4917 has two operational
amplifiers internally. The two amplifiers have externally con-
figurable gain, and the closed loop gain is set by selecting
the ratio of R
f
to R
i
. Consequently, the gain for each channel
of the IC is
A
V
= -(R
f
/ R
i
)
Since this an output ground-referenced amplifier, by driving
the headphone through R
(Pin 11) and L
(Pin 8), the
LM4917 does not require output coupling capacitors. The
typical single-ended amplifier configuration where one side
of the load is connected to ground requires large, expensive
output capacitors.
POWER DISSIPATION
Power dissipation is a major concern when using any power
amplifier and must be thoroughly understood to ensure a
successful design. 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 LM4917 has two operational amplifiers in one
package, the maximum internal power dissipation point is
twice that of the number which results from Equation 1. Even
with the large internal power dissipation, the LM4917 does
not require heat sinking over a large range of ambient tem-
perature. From Equation 1, assuming a 3V power supply and
a 16
load, the maximum power dissipation point is 28mW
per amplifier. Thus the maximum package dissipation point
is 56mW. The maximum power dissipation point obtained
must not be greater than the power dissipation that results
from Equation 2:
P
DMAX
= (T
JMAX
- T
A
) / (
θ
JA
)
(2)
For package TSSOP,
θ
= 109C/W. T
= 150C for the
LM4917. Depending on the ambient temperature, T
, of the
system surroundings, Equation 2 can be used to find the
maximum internal power dissipation supported by the IC
packaging. If the result of Equation 1 is greater than that of
Equation 2, then either the supply voltage must be de-
creased, the load impedance increased or T
reduced. For
the typical application of a 3V power supply, with a 16
load,
the maximum ambient temperature possible without violating
the maximum junction temperature is approximately 119.9C
provided that device operation is around the maximum
power dissipation point. 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 Perfor-
mance Characteristics
curves for power dissipation infor-
mation for lower output powers.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. Applications that employ a 3V power supply typi-
cally use a 4.7μF in parallel with a 0.1μF ceramic filter
capacitors to stabilize the power supply’s output, reduce
noise on the supply line, and improve the supply’s transient
response. However, their presence does not eliminate the
need for a local 0.1μF supply bypass capacitor, C
, con-
nected between the LM4917’s supply pins and ground. Keep
the length of leads and traces that connect capacitors be-
tween the LM4917’s power supply pin and ground as short
as possible.
MICRO POWER SHUTDOWN
The voltage applied to the SD_LC (shutdown left channel)
pin and the SD_RC (shutdown right channel) pin controls the
LM4917’s shutdown function. When active, the LM4917’s
micropower shutdown feature turns off the amplifiers’ bias
circuitry, reducing the supply current. The trigger point is
0.3*CPV
for a logic-low level, and 0.7*CPV
for logic-
high level. The low 0.01μA(typ) shutdown current is achieved
by appling a voltage that is as near as ground a possible to
the SD_LC/SD_RC pins.Avoltage that is higher than ground
may increase the shutdown current.
There are a few ways to control the micro-power shutdown.
These include using a single-pole, single-throw switch, a
microprocessor, or a microcontroller. When using a switch,
connect an external 100k
pull-up resistor between the
SD_LC/SD_RC pins and V
DD
. Connect the switch between
the SD_LC/SD_RC pins and ground. Select normal amplifier
L
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11
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4917SD/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 |
| LM4917SDBD | 功能描述:音頻 IC 開發(fā)工具 LM4917SD 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 |
| LM4917SDBD/NOPB | 制造商:Texas Instruments 功能描述:Ground-Referenced, 95mW Stereo Headphone Amplifier Evaluation Board |
| LM4917SDX | 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 |
| LM4917SDX/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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