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參數(shù)資料
| 型號： | LM1876T |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | Overture⑩ Audio Power Amplifier Series Dual 20W Audio Power Amplifier with Mute and Standby Modes |
| 中文描述： | 22 W, 2 CHANNEL, AUDIO AMPLIFIER, PZFM15 |
| 封裝： | PLASTIC, TO-220, 15 PIN |
| 文件頁數(shù)： | 12/16頁 |
| 文件大?。?/td> | 593K |
| 代理商： | LM1876T |
Application Information
MUTE MODE
By placing a logic-high voltage on the mute pins, the signal
going into the amplifiers will be muted. If the mute pins are
left floating or connected to a logic-low voltage, the amplifi-
ers will be in a non-muted state. There are two mute pins,
one for each amplifier, so that one channel can be muted
without muting the other if the application requires such a
configuration. Refer to the
Typical Performance Character-
istics
section for curves concerning Mute Attenuation vs
Mute Pin Voltage.
STANDBY MODE
The standby mode of the LM1876 allows the user to drasti-
cally reduce power consumption when the amplifiers are
idle. By placing a logic-high voltage on the standby pins, the
amplifiers will go into Standby Mode. In this mode, the cur-
rent drawn from the V
supply is typically less than 10 μA
total for both amplifiers. The current drawn from the V
sup-
ply is typically 4.2 mA. Clearly, there is a significant reduction
in idle power consumption when using the standby mode.
There are two Standby pins, so that one channel can be put
in standby mode without putting the other amplifier in
standby if the application requires such flexibility. Refer to
the
Typical Performance Characteristics
section for
curves showing Supply Current vs. Standby Pin Voltage for
both supplies.
UNDER-VOLTAGE PROTECTION
Upon system power-up, the under-voltage protection cir-
cuitry allows the power supplies and their corresponding ca-
pacitors to come up close to their full values before turning
on the LM1876 such that no DC output spikes occur. Upon
turn-off, the output of the LM1876 is brought to ground be-
fore the power supplies such that no transients occur at
power-down.
OVER-VOLTAGE PROTECTION
The LM1876 contains over-voltage protection circuitry that
limits the output current to approximately 3.5 Apk while also
providing voltage clamping, though not through internal
clamping diodes. The clamping effect is quite the same,
however, the output transistors are designed to work alter-
nately by sinking large current spikes.
SPiKe PROTECTION
The
LM1876
peak-temperature stressing of the power transistor array.
The Safe Operating graph in the
Typical Performance
Characteristics
section shows the area of device operation
where
SPiKe
Protection Circuitry is not enabled. The wave-
form to the right of the SOA graph exemplifies how the dy-
namic protection will cause waveform distortion when en-
abled.
is
protected
from
instantaneous
THERMAL PROTECTION
The LM1876 has a sophisticated thermal protection scheme
to prevent long-term thermal stress of the device. When the
temperature on the die reaches 165C, the LM1876 shuts
down. It starts operating again when the die temperature
drops to about 155C, but if the temperature again begins to
rise, shutdown will occur again at 165C. Therefore, the de-
vice is allowed to heat up to a relatively high temperature if
the fault condition is temporary, but a sustained fault will
cause the device to cycle in a Schmitt Trigger fashion be-
tween the thermal shutdown temperature limits of 165C and
155C. This greatly reduces the stress imposed on the IC by
thermal cycling, which in turn improves its reliability under
sustained fault conditions.
Since the die temperature is directly dependent upon the
heat sink used, the heat sink should be chosen such that
thermal shutdown will not be reached during normal opera-
tion. Using the best heat sink possible within the cost and
space constraints of the system will improve the long-term
reliability of any power semiconductor device, as discussed
in the
Determining the Correct Heat Sink
Section.
DETERMlNlNG MAXIMUM POWER DISSIPATION
Power dissipation within the integrated circuit package is a
very important parameter requiring a thorough understand-
ing if optimum power output is to be obtained. An incorrect
maximum power dissipation calculation may result in inad-
equate heat sinking causing thermal shutdown and thus lim-
iting the output power.
Equation (1) exemplifies the theoretical maximum power dis-
sipation point of each amplifier where V
CC
is the total supply
voltage.
P
DMAX
= V
CC
2/2
π
2
R
L
Thus by knowing the total supply voltage and rated output
load, the maximum power dissipation point can be calcu-
lated. The package dissipation is twice the number which re-
sults from equation (1) since there are two amplifiers in each
LM1876. Refer to the graphs of Power Dissipation versus
Output Power in the
Typical Performance Characteristics
section which show the actual full range of power dissipation
not just the maximum theoretical point that results from
equation (1).
(1)
DETERMINING THE CORRECT HEAT SINK
The choice of a heat sink for a high-power audio amplifier is
made entirely to keep the die temperature at a level such
that the thermal protection circuitry does not operate under
normal circumstances.
The thermal resistance from the die (junction) to the outside
air (ambient) is a combination of three thermal resistances,
θ
,
θ
, and
θ
. In addition, the thermal resistance,
θ
JC
(junction to case), of the LM1876TF is 2C/W and the
LM1876T is 1C/W. Using Thermalloy Thermacote thermal
compound, the thermal resistance,
θ
(case to sink), is
about 0.2C/W. Since convection heat flow (power dissipa-
tion) is analogous to current flow, thermal resistance is
analogous to electrical resistance, and temperature drops
are analogous to voltage drops, the power dissipation out of
the LM1876 is equal to the following:
P
DMAX
= (T
JMAX
T
AMB
)/
θ
JA
where T
JMAX
= 150C, T
AMB
is the system ambient tempera-
ture and
JA
=
θ
JC
+
θ
CS
+
θ
SA
.
Once the maximum package power dissipation has been
calculated using equation (1), the maximum thermal resis-
tance,
θ
, (heat sink to ambient) in C/W for a heat sink can
be calculated. This calculation is made using equation (3)
which is derived by solving for
θ
SA
in equation (2).
θ
SA
= [(T
JMAX
T
AMB
)P
DMAX
(
θ
JC
+
θ
CS
)]/P
DMAX
Again it must be noted that the value of
θ
is dependent
upon the system designer’s amplifier requirements. If the
ambient temperature that the audio amplifier is to be working
(2)
(3)
www.national.com
12
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| LM1881-X | LM1881 Video Sync Separator |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM1876T/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM1876TF | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM1876TF | 制造商:Texas Instruments 功能描述:IC AMP AUDIO DUAL 20W |
| LM1876TF/NOPB | 功能描述:音頻放大器 RoHS:否 制造商:STMicroelectronics 產(chǎn)品:General Purpose Audio Amplifiers 輸出類型:Digital 輸出功率: THD + 噪聲: 工作電源電壓:3.3 V 電源電流: 最大功率耗散: 最大工作溫度: 安裝風格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
| LM1877 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Dual Audio Power Amplifier |
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