- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄385487 > LM4929 (National Semiconductor Corporation) Stereo 40mW Low Noise Headphone Amplifier with OCL Output PDF資料下載
參數(shù)資料
| 型號： | LM4929 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Stereo 40mW Low Noise Headphone Amplifier with OCL Output |
| 中文描述： | 立體聲耳機(jī)40mW的低噪聲放大器輸出的八達(dá)通卡 |
| 文件頁數(shù)： | 10/13頁 |
| 文件大?。?/td> | 899K |
| 代理商： | LM4929 |
Application Information
AMPLIFIER CONFIGURATION EXPLANATION
As shown in
Figure 1
, the LM4929 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 LM4929 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 LM4929 has a
major advantage over single supply, single-ended amplifiers.
Since the outputs V
A, V
B, and V
C are all biased at 1/2
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.
The LM4929 eliminates these output coupling capacitors by
running in OCL mode. Unless shorted to ground, VoC is
internally configured to apply a 1/2 V
DD
bias voltage to a
stereo headphone jack’s sleeve. This voltage matches the
bias voltage present on VoA and VoB 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 LM4929’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 LM4929 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 LM4929 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 LM4929 has three operational amplifiers in one
package, the maximum power dissipation increases due to
the use of the third amplifier as a buffer and is given in
Equation 2:
P
DMAX
= 4(V
DD
)
2
/ (2
π
2
R
L
)
(2)
The maximum power dissipation point obtained from Equa-
tion 2 must not be greater than the power dissipation that
results from Equation 3:
P
DMAX
= (T
JMAX
- T
A
) /
θ
JA
(3)
For package MUB10A,
θ
= 190C/W. T
= 150C for
the LM4929. Depending 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, 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 32
load,
the maximum ambient temperature possible without violating
the maximum junction temperature is approximately 144C
provided that device operation is around the maximum
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 Perfor-
mance Characteristics curves for power dissipation informa-
tion 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 LM4929. A bypass
capacitor value in the range of 0.1μF to 1μF is recommended
for C
S
.
MICRO POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4929’s shutdown function. Activate micro-power shut-
down by applying a logic-low voltage to the SHUTDOWN
pin. When active, the LM4929’s micro-power shutdown fea-
ture turns off the amplifier’s bias circuitry, reducing the sup-
ply current. The trigger point varies depending on supply
voltage and is shown in the Shutdown Hysteresis Voltage
graphs in the Typical Performance Characteristics section.
The low 0.1μA(typ) shutdown current is achieved by apply-
ing a voltage that is as near as ground as possible to the
SHUTDOWN pin. A voltage 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 mi-
crocontroller. When using a switch, connect an external
100k
pull-up resistor between the SHUTDOWN pin and
V
DD
. Connect the switch between the SHUTDOWN pin and
ground. Select normal amplifier operation by opening the
switch. Closing the switch connects the SHUTDOWN pin to
ground, activating micro-power shutdown.
L
www.national.com
10
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| LM4929MM | Stereo 40mW Low Noise Headphone Amplifier with OCL Output |
| LM4930ITL | CAP CER 15000PF 10% 50V X7R 1206 |
| LM4930 | Audio Subsystem with Stereo Headphone & Mono Speaker Amplifiers |
| LM4935 | Audio Sub-System with Dual-Mode Stereo Headphone and Mono High Efficiency Loudspeaker Amplifiers and Multi-Purpose ADC |
| LM4935WL | Audio Sub-System with Dual-Mode Stereo Headphone and Mono High Efficiency Loudspeaker Amplifiers and Multi-Purpose ADC |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4929MM | 制造商:Texas Instruments 功能描述:Audio Amp Headphone 2-CH Stereo 0.08W Class-AB 10-Pin VSSOP T/R |
| LM4929MM/NOPB | 功能描述:音頻放大器 Stereo 40mW Lo Noise Headphone Amp 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 |
| LM4929MMBD | 功能描述:BOARD EVALUATION LM4929MM RoHS:否 類別:編程器，開發(fā)系統(tǒng) >> 評估板 - 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:1 系列:- |
| LM4929MMX/NOPB | 功能描述:音頻放大器 Stereo 40mW Lo Noise Headphone Amp 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 |
| LM492-S | 功能描述:基本/快動開關(guān) Foot Switch RoHS:否 制造商:Omron Electronics 觸點形式:SPDT 執(zhí)行器:Lever 電流額定值:5 A 電壓額定值 AC:250 V 電壓額定值 DC:30 V 功率額定值: 工作力:120 g IP 等級:IP 67 NEMA 額定值: 端接類型:Wire 安裝:Panel |
發(fā)布緊急采購，3分鐘左右您將得到回復(fù)。