- 您现在的位置：买卖IC网 > PDF目录32307 > LM4912MM/NOPB (NATIONAL SEMICONDUCTOR CORP) 0.145 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 PDF资料下载
参数资料
| 型号： | LM4912MM/NOPB |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 0.145 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 |
| 封装： | MSOP-10 |
| 文件页数： | 4/16页 |
| 文件大小： | 490K |
| 代理商： | LM4912MM/NOPB |
Application Information
AMPLIFIER CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4912 has three operational am-
plifiers internally. Two of the amplifier's have externally con-
figurable 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 selecting the ratio
of R
f to Ri. Consequently, the gain for each channel of the IC
is
A
VD = -(Rf / Ri)
By driving the loads through outputs V
oA and VoB with VoC
acting as a buffered bias voltage the LM4912 does not require
output coupling capacitors. The classical single-ended am-
plifier configuration where one side of the load is connected
to ground requires large, expensive output coupling capaci-
tors.
A configuration, such as the one used in the LM4912, has a
major advantage over single supply, single-ended amplifiers.
Since the outputs V
oA, VoB, and VoC are all biased at 1/2
V
DD, no net DC voltage exists across each load. This elimi-
nates the need for output coupling capacitors which are re-
quired 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.
POWER DISSIPATION
Power dissipation is a major concern when using any power
amplifier and must be thoroughly understood to ensure a suc-
cessful 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 = (VDD)
2
/ (2
π2R
L)
(1)
Since the LM4912 has two operational amplifiers in one pack-
age, the maximum internal power dissipation point is twice
that of the number which results from Equation 1. From Equa-
tion 1, assuming a 3V power supply and a 32
load, the
maximum power dissipation point is 14mW per amplifier.
Thus the maximum package dissipation point is 28mW.
The maximum power dissipation point obtained from Equa-
tion 1 must not be greater than the power dissipation that
results from Equation 2:
P
DMAX = (TJMAX - TA) / θJA
(2)
For package MUB10A,
θ
JA = 190°C/W. TJMAX = 150°C for the
LM4912. Depending on the ambient temperature, T
A, 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 decreased,
the load impedance increased or T
A reduced. For the typical
application of a 3V power supply, with an 32
load, the max-
imum ambient temperature possible without violating the
maximum junction temperature is approximately 144°C pro-
vided that device operation is around the maximum power
dissipation point. Thus, for typical applications, power dissi-
pation is not an issue. Power dissipation is a function of output
power and thus, if typical operation is not around the maxi-
mum power dissipation point, the ambient temperature may
be increased accordingly. Refer to the Typical Performance
Characteristics curves for power dissipation 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 LM4912. A bypass ca-
pacitor value in the range of 0.1F to 1F is recommended
for C
S.
MICRO POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4912's shutdown function. Activate micro-power shutdown
by applying a logic-low voltage to the SHUTDOWN pin. When
active, the LM4912's micro-power shutdown feature turns off
the amplifier's bias circuitry, reducing the supply 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 0.1A(typ)
shutdown current is achieved by applying 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 mi-
croprocessor, or a microcontroller. 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 opera-
tion by opening the switch. Closing the switch connects the
SHUTDOWN pin to ground, activating micro-power shut-
down.
The switch and resistor guarantee that the SHUTDOWN pin
will not float. This prevents unwanted state changes. In a sys-
tem with a microprocessor or microcontroller, use a digital
output to apply the control voltage to the SHUTDOWN pin.
Driving the SHUTDOWN pin with active circuitry eliminates
the pull-up resistor.
Shutdown enable/disable times are controlled by a combina-
tion of C
B and VDD. Larger values of CB results in longer turn
on/off times from Shutdown. Smaller Vdd values also in-
crease turn on/off time for a given value of C
B. Longer shut-
down times also improve the LM4912's resistance to click and
pop upon entering or returning from shutdown. For a 2.4V
supply and C
B = 4.7F, the LM4912 requires about 2 seconds
to enter or return from shutdown. This longer shutdown time
enables the LM4912 to have virtually zero pop and click tran-
sients upon entering or release from shutdown.
Smaller values of C
B will decrease turn-on time, but at the cost
of increased pop and click and reduced PSRR. Since shut-
down enable/disable times increase dramatically as supply
voltage gets below 2.2V, this reduced turn-on time may be
desirable if extreme low supply voltage levels are used as this
would offset increases in turn-on time caused by the lower
supply voltage.
www.national.com
12
LM4912
相关PDF资料 |
PDF描述 |
|---|---|
| LM581JH | 1-OUTPUT THREE TERM VOLTAGE REFERENCE, 10 V, MBCY3 |
| LM581TH | 1-OUTPUT THREE TERM VOLTAGE REFERENCE, 10 V, MBCY3 |
| LM6181IM/NOPB | VIDEO AMPLIFIER, PDSO16 |
| LM8500HVA9/NOPB | SPECIALTY CONSUMER CIRCUIT, PQCC44 |
| LM8500IMT9/NOPB | SPECIALTY CONSUMER CIRCUIT, PDSO48 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LM4912MMX/NOPB | 功能描述:IC AMP AUDIO PWR .145W AB 10MSOP RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Boomer® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR) |
| LM4913 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:2W Monaural, 90mW Stereo Headphone Audio Amplifier |
| LM4913A WAF | 制造商:Texas Instruments 功能描述: |
| LM4913MH | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM4913MH/NOPB | 功能描述:IC AMP AUDIO MONO/STER 10TSSOP RoHS:是 类别:集成电路 (IC) >> 线性 - 音頻放大器 系列:Boomer® 产品培训模块:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 标准包装:2,500 系列:DirectDrive® 类型:H 类 输出类型:耳机，2-通道（立体声） 在某负载时最大输出功率 x 通道数量:35mW x 2 @ 16 欧姆 电源电压:1.62 V ~ 1.98 V 特点:I²C，麦克风，静音，短路保护，音量控制 安装类型:表面贴装 供应商设备封装:25-WLP（2.09x2.09） 封装/外壳:25-WFBGA，WLCSP 包装:带卷 (TR) |
发布紧急采购，3分钟左右您将得到回复。