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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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The trigger point between a logic low and logic high level is  
typically half supply. It is best to switch between ground and  
the supply VDD to provide maximum device performance. By  
switching the shutdown pin to VDD, the LM4863 supply cur-  
rent draw will be minimized in idle mode. While the device  
Application Information (Continued)  
POWER DISSIPATION  
Whether the power amplifier is bridged or single-ended,  
power dissipation is a major concern when designing the  
amplifier. Equation 1 states the maximum power dissipation  
point for a single-ended amplifier operating at a given supply  
voltage and driving a specified load.  
will be disabled with shutdown pin voltages less than VDD  
,
the idle current may be greater than the typical value of  
0.7 µA. In either case, the shutdown pin should be tied to a  
definite voltage to avoid unwanted state changes.  
PDMAX (VDD)2/(2π2RL): Single-Ended  
(1)  
=
In many applications, a microcontroller or microprocessor  
output is used to control the shutdown circuitry which pro-  
vides a quick, smooth transition into shutdown. Another solu-  
tion is to use a single-pole, single-throw switch in conjunction  
with an external pull-up resistor. When the switch is closed,  
the shutdown pin is connected to ground and enables the  
amplifier. If the switch is open, then the external pull-up re-  
sistor will disable the LM4863. This scheme guarantees that  
the shutdown pin will not float, thus preventing unwanted  
state changes.  
However, a direct consequence of the increased power de-  
livered to the load by a bridge amplifier is an increase in in-  
ternal power dissipation. Equation 2 states the maximum  
power dissipation point for a bridge amplifier operating at the  
same given conditions.  
=
*
PDMAX  
4
(VDD)2/(2π2RL): Bridge Mode (2)  
Since the LM4863 is a dual channel power amplifier, the  
maximum internal power dissipation is 2 times that of Equa-  
tion 1 or Equation 2 depending on the mode of operation.  
Even with this substantial increase in power dissipation, the  
LM4863 does not require heatsinking. The power dissipation  
from Equation 2, assuming a 5V power supply and an 8Ω  
load, must not be greater than the power dissipation that re-  
sults from Equation 3:  
HP-IN FUNCTION  
The LM4863 possesses a headphone control pin that turns  
off the amplifiers which drive +OutA and +OutB so that  
single-ended operation can occur and a bridged connected  
load is muted. Quiescent current consumption is reduced  
when the IC is in this single-ended mode.  
=
PDMAX (TJMAX − TA)/θJA  
(3)  
=
For packages M16A and MTA20, θJA  
80˚C/W, and for  
=
=
package N16A, θJA  
63˚C/W. TJMAX  
150˚C for the  
Figure 2 shows the implementation of the LM4863’s head-  
phone control function using a single-supply headphone am-  
plifier. The voltage divider of R1 and R2 sets the voltage at  
the HP-IN pin (pin 16) to be approximately 50 mV when there  
are no headphones plugged into the system. This logic-low  
voltage at the HP-IN pin enables the LM4863 and places it in  
bridged mode operation. Resistor R4 limits the amount of  
current flowing out of the HP-IN pin when the voltage at that  
pin goes below ground resulting from the music coming from  
the headphone amplifier. The output coupling capacitors pro-  
tect the headphones by blocking the amplifier’s half supply  
DC voltage.  
LM4863. Depending on the ambient temperature, TA, 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 the ambient tem-  
perature reduced. For the typical application of a 5V power  
supply, with an 8bridged load, the maximum ambient tem-  
perature possible without violating the maximum junction  
temperature is approximately 48˚C provided that device op-  
eration is around the maximum power dissipation point and  
assuming surface mount packaging. Internal power dissipa-  
tion 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 Perfor-  
mance Characteristics curves for power dissipation infor-  
mation for different output powers.  
When there are no headphones plugged into the system and  
the IC is in bridged mode configuration, both loads are es-  
sentially at a 0V DC potential. Since the HP-IN threshold is  
set at 4V, even in an ideal situation, the output swing cannot  
cause a false single-ended trigger.  
When a set of headphones are plugged into the system, the  
contact pin of the headphone jack is disconnected from the  
signal pin, interrupting the voltage divider set up by resistors  
POWER SUPPLY BYPASSING  
As with any power amplifier, proper supply bypassing is criti-  
cal for low noise performance and high power supply rejec-  
tion. 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 applica-  
tions employ a 5V regulator with 10 µF and a 0.1 µF bypass  
capacitors which aid in supply filtering. This does not elimi-  
nate the need for bypassing the supply nodes of the  
R1 and R2. Resistor R1 then pulls up the HP-IN pin, en-  
abling the headphone function. This disables the second  
side of the amplifier thus muting the bridged speakers. The  
amplifier then drives the headphones, whose impedance is  
in parallel with resistors R2 and R3. Resistors R2 and R3  
have negligible effect on output drive capability since the  
typical impedance of headphones are 32. Also shown in  
Figure 2 are the electrical connections for the headphone  
jack and plug. A 3-wire plug consists of a Tip, Ring and  
Sleave, where the Tip and Ring are signal carrying conduc-  
tors and the Sleave is the common ground return. One con-  
trol pin contact for each headphone jack is sufficient to indi-  
cate to control inputs that the user has inserted a plug into a  
jack and that another mode of operation is desired.  
LM4863. 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.  
The LM4863 can be used to drive both a pair of bridged 8Ω  
speakers and a pair of 32headphones without using the  
HP-IN pin. In this case the HP-IN would not be connected to  
the headphone jack but to a microprocessor or a switch. By  
enabling the HP-IN pin, the 8speakers can be muted.  
SHUTDOWN FUNCTION  
In order to reduce power consumption while not in use, the  
LM4863 contains a shutdown pin to externally turn off the  
amplifier’s bias circuitry. This shutdown feature turns the am-  
plifier off when a logic high is placed on the shutdown pin.  
9
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