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LM4863MT 参数 Datasheet PDF下载

LM4863MT图片预览
型号: LM4863MT
PDF下载: 下载PDF文件 查看货源
内容描述: 双2.2W音频放大器加上立体声耳机功能 [Dual 2.2W Audio Amplifier Plus Stereo Headphone Function]
分类和应用: 音频放大器
文件页数/大小: 16 页 / 515 K
品牌: NSC [ National Semiconductor ]
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Non-MTE Specific Characteristics (Continued)  
Power Supply  
Rejection Ratio  
Open Loop  
Frequency Response  
Supply Current vs  
Supply Voltage  
DS012881-23  
DS012881-21  
DS012881-22  
Output power is also dependent on supply regulation. To  
keep the supply voltage from sagging under full output  
power conditions, the supply traces should be as wide as  
practical.  
Application Information  
EXPOSED-DAP MOUNTING CONSIDERATIONS  
The exposed-DAP must be connected to ground. The  
exposed-DAP package of the LM4863MTE requires special  
attention to thermal design. If thermal design issues are not  
properly addressed, an LM4863MTE driving 4will go into  
thermal shutdown.  
BRIDGE CONFIGURATION EXPLANATION  
As shown in Figure 1, the LM4863 has two pairs of opera-  
tional amplifiers internally, allowing for a few different ampli-  
fier configurations. The first amplifier’s gain is externally con-  
figurable, 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 Rf to R i while  
the second amplifier’s gain is fixed by the two internal 20 kΩ  
resistors. Figure 1 shows that the output of amplifier one  
serves as the input to amplifier two which results in both am-  
plifiers producing signals identical in magnitude, but out of  
phase 180˚. Consequently, the differential gain for each  
channel of the IC is  
The exposed-DAP on the bottom of the LM4863MTE should  
be soldered down to a copper pad on the circuit board. Heat  
is conducted away from the exposed-DAP by a copper  
plane. If the copper plane is not on the top surface of the cir-  
cuit board, 8 to 10 vias of 0.013 inches or smaller in diameter  
should be used to thermally couple the exposed-DAP to the  
plane. For good thermal conduction, the vias must be  
plated-through and solder-filled.  
The copper plane used to conduct heat away from the  
exposed-DAP should be as large as pratical. If the plane is  
on the same side of the circuit board as the exposed-DAP,  
2.5in2 is the minimum for 5V operation into 4. If the heat  
sink plane is buried or not on the same side as the exposed-  
DAP, 5in2 is the minimum for 5V operation into 4. If the am-  
bient temperature is higher than 25˚C, a larger copper plane  
or forced-air cooling will be required to keep the  
LM4863MTE junction temperature below the thermal shut-  
down temperature (150˚C). See the power derating curve for  
the LM4863MTE for derating information.  
=
*
(Rf/R )  
i
AVD  
2
By driving the load differentially through outputs +OutA and  
−OutA or +OutB and −OutB, an amplifier configuration com-  
monly 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 con-  
nected 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 the output swing for a speci-  
fied supply voltage. Four times the output power is possible  
as compared to a single-ended amplifier under the same  
conditions. This increase in attainable output power as-  
sumes that the amplifier is not current limited or clipped. In  
order to choose an amplifier’s closed-loop gain without caus-  
ing excessive clipping, please refer to the Audio Power Am-  
plifier Design section.  
The LM4863MTE requires forced-air cooling when operating  
into 3. With the part attached to 2.5in2 of exposed copper,  
with a 3load, and with an ambient temperature of 25˚C,  
450 linear-feet per minute kept the part out of thermal shut-  
down. In higher ambient temperatures, higher airflow rates  
and/or larger copper areas will be required to keep the part  
out of thermal shutdown.  
See DEMOBOARD CIRCUIT LAYOUT for an example of an  
A bridge configuration, such as the one used in LM4863,  
also creates a second advantage over single-ended amplifi-  
ers. Since the differential outputs, +OutA, −OutA, +OutB,  
and −OutB, are biased at half-supply, no net DC voltage ex-  
ists across the load. This eliminates the need for an output  
coupling capacitor which is required in a single supply,  
single-ended amplifier configuration. If an output coupling  
capacitor is not used in a single-ended configuration, the  
half-supply bias across the load would result in both in-  
creased internal IC power dissipation as well as permanent  
loudspeaker damage.  
exposed-DAP TSSOP circuit board layout.  
3& 4LAYOUT CONSIDERATIONS  
With low impedance loads, the output power at the loads is  
heavily dependent on trace resistance from the output pins  
of the LM4863. Traces from the output of the LM4863MTE to  
the load or load connectors should be as wide as practical.  
Any resistance in the output traces will reduce the power de-  
livered to the load. For example, with a 4load and 0.1of  
trace resistance in each output, output power at the load  
drops from 2.2W to 2.0W  
www.national.com  
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