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参数资料
| 型号： | LM4864MWC |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 0.55 W, 1 CHANNEL, AUDIO AMPLIFIER, UUC13 |
| 封装： | WAFER |
| 文件页数： | 3/18页 |
| 文件大小： | 589K |
| 代理商： | LM4864MWC |
Application Information
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1, the LM4864 has two operational
amplifiers internally, allowing for a few different amplifier
configurations. The first amplifier’s gain is externally config-
urable, while the second amplifier is internally fixed in a
unity-gain, inverting configuration. The closed-loop gain of
the first amplifier is set by selecting the ratio of R
F to Ri while
the second amplifier’s gain is fixed by the two internal 10k
resistors. Figure 1 shows that the output of amplifier one
serves as the input to amplifier two which results in both
amplifiers producing signals identical in magnitude, but out
of phase 180. Consequently, the differential gain for the IC
is
A
VD = 2*(RF/Ri)
By driving the load differentially through outputs V
o1 and Vo2,
an amplifier configuration commonly referred to as “bridged
mode” is established. Bridged mode operation is different
from the classical single-ended amplifier configuration where
one side of its load is connected to ground.
A bridge amplifier design has a few distinct advantages over
the single-ended configuration, as it provides differential
drive to the load, thus doubling output swing for a specified
supply voltage. Four times the output power is possible as
compared to a single-ended amplifier under the same con-
ditions. This increase in attainable output power assumes
that the amplifier is not current limited or clipped. In order to
choose an amplifier’s closed-loop gain without causing ex-
cessive clipping, please refer to the Audio Power Amplifier
Design section.
A bridge configuration, such as the one used in LM4864,
also creates a second advantage over single-ended amplifi-
ers. Since the differential outputs, V
o1 and Vo2, are biased at
half-supply, no net DC voltage exists across the load. This
eliminates the need for an output coupling capacitor which is
required in a single supply, single-ended amplifier configura-
tion. If an output coupling capacitor is not used in a single-
ended configuration, the half-supply bias across the load
would result in both increased internal lC power dissipation
as well as permanent loudspeaker damage.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifier, whether the amplifier is bridged or
single-ended. Equation 1 states the maximum power dissi-
pation point for a bridge amplifier operating at a given supply
voltage and driving a specified output load.
P
DMAX =(VDD)
2/(2
π2R
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 point for a bridge amplifier oper-
ating at the same conditions.
P
DMAX = 4(VDD)
2/(2
π2R
L)
Bridge Mode (2)
Since the LM4864 has two operational amplifiers in one
package, the maximum internal power dissipation is 4 times
that of a single-ended amplifier. Even with this substantial
increase in power dissipation, the LM4864 does not require
heatsinking. From Equation 1, assuming a 5V power supply
and an 8
load, the maximum power dissipation point is
633 mW. The maximum power dissipation point obtained
from Equation 2 must not be greater than the power dissi-
pation that results from Equation 3:
P
DMAX =(TJMAX TA)/
θ
JA
(3)
For package MUA08A,
θ
JA = 210C/W, for package M08A,
θ
JA = 170C/W, for package N08E,
θ
JA = 107C/W, and for
package LDA10A,
θ
JA = 63C/W. TJMAX = 150C for the
LM4864. Depending on the ambient temperature, T
A,ofthe
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, the ambient tem-
perature reduced, or the
θ
JA reduced with heatsinking. In
many cases larger traces near the output, V
DD, and GND
pins can be used to lower the
θ
JA. The larger areas of copper
provide a form of heatsinking allowing a higher power dissi-
pation. For the typical application of a 5V power supply, with
an 8
load, the maximum ambient temperature possible
without violating the maximum junction temperature is ap-
proximately 44C provided that device operation is around
the maximum power dissipation point and assuming surface
mount packaging. Internal power dissipation is a function of
output power. If typical operation is not around the maximum
power dissipation point, the ambient temperature can be
increased. Refer to the Typical Performance Characteris-
tics curves for power dissipation information for lower output
powers.
EXPOSED-DAP PACKAGE PCB MOUNTING
CONSIDERATION
The LM4864’s exposed-dap (die attach paddle) package
(LD) provides a low thermal resistance between the die and
the PCB to which the part is mounted and soldered. This
allows rapid heat transfer from the die to the surrounding
PCB copper traces, ground plane, and surrounding air.
The LD package should have its DAP soldered to a copper
pad on the PCB. The DAP’s PCB copper pad may be con-
nected to a large plane of continuous unbroken copper. This
plane forms a thermal mass, heat sink, and radiation area.
Further detailed and specific information concerning PCB
layout, fabrication, and mounting an LD (LLP) package is
available from National Semiconductor’s Package Engineer-
ing Group under application note AN1187.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. The capacitor location on both the bypass and
power supply pins should be as close to the device as
possible. The effect of a larger half supply bypass capacitor
is improved PSRR due to increased half-supply stability.
Typical applications employ a 5V regulator with 10 F and a
0.1 F bypass capacitors which aid in supply stability, but do
not eliminate the need for bypassing the supply nodes of the
LM4864. The selection of bypass capacitors, especially C
B,
is thus dependent upon desired PSRR requirements, click
and pop performance as explained in the section, Proper
Selection of External Components, system cost, and size
constraints.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4864 contains a shutdown pin to externally turn off the
amplifier’s bias circuitry. This shutdown feature turns the
amplifier off when a logic high is placed on the shutdown pin.
The trigger point between a logic low and logic high level is
typically half supply. It is best to switch between ground and
supply to provide maximum device performance. By switch-
ing the shutdown pin to V
DD, the LM4864 supply current
LM4864
www.national.com
11
相关PDF资料 |
PDF描述 |
|---|---|
| LM4864N/NOPB | 0.675 W, 1 CHANNEL, AUDIO AMPLIFIER, PDIP8 |
| LM4864LD/NOPB | 0.725 W, 1 CHANNEL, AUDIO AMPLIFIER, DSO10 |
| LM4865IBP/NOPB | 1 CHANNEL(S), VOLUME CONTROL CIRCUIT, PBGA8 |
| LM4865IBPX/NOPB | 1 CHANNEL(S), VOLUME CONTROL CIRCUIT, PBGA8 |
| LM4865IBPX | 1 CHANNEL(S), VOLUME CONTROL CIRCUIT, PBGA8 |
相关代理商/技术参数 |
参数描述 |
|---|---|
| LM4864MX | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| LM4864MX/NOPB | 功能描述:音频放大器 RoHS:否 制造商:STMicroelectronics 产品:General Purpose Audio Amplifiers 输出类型:Digital 输出功率: THD + 噪声: 工作电源电压:3.3 V 电源电流: 最大功率耗散: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:TQFP-64 封装:Reel |
| LM4864N | 功能描述:IC AMP AUDIO PWR .725W MONO 8DIP RoHS:否 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) |
| LM4865 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:750 mW Audio Power Amplifier with DC Volume Control and Headphone Switch |
| LM4865IBP | 制造商:Texas Instruments 功能描述: |
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