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參數(shù)資料
| 型號： | LM4854MM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 0.2 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO10 |
| 封裝： | 0.118 INCH, 0.50 MM PITCH, TSSOP-10 |
| 文件頁數(shù)： | 7/23頁 |
| 文件大小： | 1795K |
| 代理商： | LM4854MM |
Application Information (Continued)
The LM4854’s TJMAX = 150C. In the IBL package, the
LM4854’s
θ
JA is 150C/W. The LM4854’s TJMAX = 150C. In
the LD package soldered to a DAP pad that expands to a
copper area of 2.5in
2 on a PCB, the LM4854’s
θ
JA is 42C/W.
In the MT package, the LM4854’s
θ
JA is 80C/W. At any
given ambient temperature T
A, use Equation (4) to find the
maximum internal power dissipation supported by the IC
packaging. Rearranging Equation (4) and substituting P
DMAX
for P
DMAX’ results in Equation (5). This equation gives the
maximum ambient temperature that still allows maximum
stereo power dissipation without violating the LM4854’s
maximum junction temperature.
T
A =TJMAX -PDMAX-MONOBTLθJA
(5)
For a typical application with a 5V power supply and an 8
load, the maximum ambient temperature that allows maxi-
mum stereo power dissipation without exceeding the maxi-
mum junction temperature is approximately 102C for the
IBL package.
T
JMAX =PDMAX-MONOBTLθJA +TA
(6)
Equation (6) gives the maximum junction temperature T
J-
MAX
. If the result violates the LM4854’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 (3) is
greater than that of Equation (4), 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
JA. The heat sink can be created
using additional copper area around the package, with con-
nections 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
JA is the sum of θJC, θCS, and
θ
SA.(θJC is the junction-to-case thermal impedance, θCS is
the case-to-sink thermal impedance, and
θ
SA is the sink-to-
ambient thermal impedance.) Refer to the Typical Perfor-
mance Characteristics curves for power dissipation informa-
tion at lower output 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 10F in parallel with a 0.1F filter capacitors to stabi-
lize 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 1.0F
tantalum bypass capacitance connected between the
LM4854’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 LM4854’s power supply pin and
ground as short as possible. Connecting a 1F capacitor,
CB, between the BYPASS pin and ground improves the
internal bias voltage’s stability and improves the amplifier’s
PSRR. The PSRR improvements increase as the bypass pin
capacitor value increases. Too large, however, increases
turn-on time and can compromise the amplifier’s click and
pop performance. The selection of bypass capacitor values,
especially CB, depends on desired PSRR requirements,
click and pop performance (as explained in the section,
Proper Selection of External Components), system cost, and
size constraints.
STANDBY
The LM4854 features a low-power, fast turn-on standby
mode. Applying a logic-low to the STANDBY pin act actives
the standby mode. When this mode is active, the power
supply current decreases to a nominal value of 30A and the
amplifier outputs are muted. Fast turn-on is assured be-
cause all bias points remain at the same voltage as when the
part is in fully active operation. The LM4854 returns to fully
active operation in 100s (typ) after the input voltage on the
STANDBY pin switches from a logic low to a logic high.
MICRO-POWER SHUTDOWN
The LM4854 features an active-low micro-power shutdown
mode. When active, the LM4854’s micro-power shutdown
feature turns off the amplifier’s bias circuitry, reducing the
supply current. The logic threshold is typically V
DD/2. The
low 0.1A typical shutdown current is achieved by applying a
voltage to the SHUTDOWN pin that is as near to GND as
possible. A voltage that is greater than GND may increase
the shutdown current.
CONTROLLING STANDBY AND MICROPOWER SHUT-
DOWN
There are a few methods to control standby or micro-power
shutdown. These include using a single-pole, single-throw
switch (SPST), a microprocessor, or a microcontroller. When
using a switch, connect a 100k
pull-up resistor between the
STANDBY or SHUTDOWN pin and V
DD and the SPST
switch between the STANDBY or SHUTDOWN pin and
GND. Select normal amplifier operation by opening the
switch. Closing the switch applies GND to the STANDBY or
SHUTDOWN pins, activating micro-power shutdown. The
switch and resistor guarantee that the STANDBY or SHUT-
DOWN pins 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 active-state voltage to
the STANDBY or SHUTDOWN pin.
HEADPHONE (SINGLE-ENDED) AMPLIFIER OPERATION
Previous single-supply amplifiers that were designed to drive
both BTL and SE loads used a SE (or headphone) ’sense’
input. This input typically required two external resistors to
bias the sense input to a preset voltage that selected BTL
operation.
The LM4854 has a unique headphone sense circuit that
eliminates the external resistors. The amplifier has an inter-
nal comparator that monitors the voltage present on the
R-OUT pin. It compares this voltage against the voltage on
the HP-SENSE pin. When these voltages are equal, BTL
mode is selected and AMP3 is shutdown and its output has
a very high impedance. When the comparator’s input signals
are different, (a typical
V of 200mV), the comparator’s
output switches and activates the SE (headphone) mode.
LM4854
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 |
|---|---|
| LM4854MT | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM4854MT/NOPB | 功能描述:IC AMP AUDIO PWR 2.3W AB 14TSSOP 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(fēng)，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) |
| LM4854MTX/NOPB | 功能描述:IC AMP AUDIO PWR 2.3W AB 14TSSOP 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(fēng)，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) |
| LM4855 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Boomer AUDIO POWER AMPLIFIER Integrated Audio Amplifier System |
| LM48555 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Ceramic Speaker Driver |
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