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參數(shù)資料
| 型號： | LM4888 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Dual 2.1W Audio Amplifier Plus Stereo Headphone & 3D Enhancement |
| 中文描述： | 雙2.1W音頻功率放大器加立體聲耳機 |
| 文件頁數(shù)： | 15/22頁 |
| 文件大小： | 1179K |
| 代理商： | LM4888 |
Application Information
(Continued)
The LM4888’s power dissipation is twice that given by Equa-
tion (2) or Equation (3) when operating in the single-ended
mode or bridge mode, respectively. Twice the maximum
power dissipation point given by Equation (3) must not ex-
ceed the power dissipation given by Equation (4):
P
DMAX
' = (T
JMAX
T
A
)/
θ
JA
The LM4888’s T
= 150C. In the SQ package soldered
to a DAP pad that expands to a copper area of 5in
2
on a
PCB, the LM4888’s
θ
is 20C/W. At any given ambient
temperature T
, use Equation (4) to find the maximum inter-
nal power dissipation supported by the IC packaging. Rear-
ranging Equation (4) and substituting P
for P
' re-
sults in Equation (5). This equation gives the maximum
ambient temperature that still allows maximum stereo power
dissipation without violating the LM4888’s maximum junction
temperature.
T
A
= T
JMAX
– 2*P
DMAX
θ
JA
For a typical application with a 5V power supply and an 4
load, the maximum ambient temperature that allows maxi-
mum stereo power dissipation without exceeding the maxi-
mum junction temperature is approximately 99C for the SQ
package.
T
JMAX
= P
DMAX
θ
JA
+ T
A
Equation (6) gives the maximum junction temperature
T
JMAX
. If the result violates the LM4888’s 150C, reduce the
maximum junction temperature by reducing the power sup-
ply voltage or increasing the load resistance. Further allow-
ance should be made for increased ambient temperatures.
The above examples assume that a device is a surface
mount part operating around the maximum power dissipation
point. Since internal power dissipation is a function of output
power, higher ambient temperatures are allowed as output
power or duty cycle decreases.
If the result of Equation (2) is greater than that of Equation
(3), then decrease the supply voltage, increase the load
impedance, or reduce the ambient temperature. If these
measures are insufficient, a heat sink can be added to
reduce
θ
. The heat sink can be created using additional
copper area around the package, with connections to the
ground pin(s), supply pin and amplifier output pins. External,
solder attached SMT heatsinks such as the Thermalloy
7106D can also improve power dissipation. When adding a
heat sink, the
θ
is the sum of
θ
,
θ
CS
, and
θ
. (
θ
is the
junction-to-case thermal impedance,
θ
CS
is the case-to-sink
(4)
(5)
(6)
thermal impedance, and
θ
is the sink-to-ambient thermal
impedance.) Refer to the
Typical Performance Character-
istics
curves for power dissipation information at lower out-
put power levels.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection. Applications that employ a 5V regulator typically
use a 10 μF in parallel with a 0.1 μF filter capacitor to
stabilize the regulator’s output, reduce noise on the supply
line, and improve the supply’s transient response. However,
their presence does not eliminate the need for a local 1.0 μF
tantalum bypass capacitance connected between the
LM4888’s supply pins and ground. Do not substitute a ce-
ramic capacitor for the tantalum. Doing so may cause oscil-
lation. Keep the length of leads and traces that connect
capacitors between the LM4888’s power supply pin and
ground as short as possible.
MICRO-POWER SHUTDOWN
The voltage applied to the SHUTDOWN pin controls the
LM4888’s shutdown function. Activate micro-power shut-
down by applying GND to the SHUTDOWN pin. When ac-
tive, the LM4888’s micro-power shutdown feature turns off
the amplifier’s bias circuitry, reducing the supply current. The
low 0.04 μAtypical shutdown current is achieved by applying
a voltage that is as near as GND as possible to the SHUT-
DOWN pin. A voltage that is more than GND may increase
the shutdown current.
Table 1
shows the logic signal levels
that activate and deactivate micro-power shutdown and
headphone amplifier operation.
There are a few ways to control the micro-power shutdown.
These include using a single-pole, single-throw switch, a
microprocessor, or a microcontroller. When using a switch,
connect an external 100k resistor between the SHUTDOWN
pin and Ground. Connect the switch between the SHUT-
DOWN pin V
DD
. Select normal amplifier operation by closing
the switch. Opening the switch sets the SHUTDOWN pin to
ground through the 100k resistor, which activates the micro-
power shutdown. The switch and resistor guarantee that the
SHUTDOWN pin will not float. This prevents unwanted state
changes. In a system with a microprocessor or a microcon-
troller, 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.
L
www.national.com
15
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM4888_06 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dual 2.1W Audio Amplifier Plus Stereo Headphone & 3D Enhancement |
| LM4888A E WAF | 制造商:Texas Instruments 功能描述: |
| LM4888SQ | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dual 2.1W Audio Amplifier Plus Stereo Headphone & 3D Enhancement |
| LM4888SQ/NOPB | 功能描述:IC AMP AUDIO PWR 3W STER 24LLP RoHS:是 類別:集成電路 (IC) >> 線性 - 音頻放大器 系列:Boomer® 產(chǎn)品培訓(xùn)模塊:Lead (SnPb) Finish for COTS Obsolescence Mitigation Program 標準包裝:2,500 系列:DirectDrive® 類型:H 類 輸出類型:耳機，2-通道（立體聲） 在某負載時最大輸出功率 x 通道數(shù)量:35mW x 2 @ 16 歐姆 電源電壓:1.62 V ~ 1.98 V 特點:I²C，麥克風，靜音，短路保護，音量控制 安裝類型:表面貼裝 供應(yīng)商設(shè)備封裝:25-WLP（2.09x2.09） 封裝/外殼:25-WFBGA，WLCSP 包裝:帶卷 (TR) |
| LM4888SQBD | 功能描述:BOARD EVALUATION LM4888SQ 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 標準包裝:1 系列:- |
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