- 您現(xiàn)在的位置：買賣IC網(wǎng) > PDF目錄358866 > LM4732 (National Semiconductor Corporation) Stereo 50W Audio Power Amplifier with Mute PDF資料下載
參數(shù)資料
| 型號： | LM4732 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | Stereo 50W Audio Power Amplifier with Mute |
| 中文描述： | 50瓦立體聲音頻功率放大器與靜音 |
| 文件頁數(shù)： | 13/22頁 |
| 文件大?。?/td> | 861K |
| 代理商： | LM4732 |
Application Information
MUTE MODE
The muting function allows the user to mute the amplifier.
This can be accomplished as shown in the Typical Applica-
tion Circuit. The resistor R
M
is chosen with reference to the
negative supply voltage and is used in conjunction with a
switch. The switch, when opened or switched to GND, cuts
off the current flow from the MUTE pins to V
EE
, thus placing
the LM4732 into mute mode. Refer to the Mute Attenuation
vs Mute Current curves in the
Typical Performance Char-
acteristics
section for values of attenuation per current out
of each MUTE pin. The resistance R
M
is calculated by the
following equation:
R
M
≤
(|V
EE
| 2.6V) / I
MUTE
Where I
MUTE
≥
0.5mA for each MUTE pin.
The MUTE pins can be tied together so that only one resistor
is required for the mute function. The mute resistor value
must be chosen so that a minimum of 1mA is pulled through
the resistor R
. This ensures that each amplifier is fully
operational. Taking into account supply line fluctuations, it is
a good idea to pull out 1mA per MUTE pin or 2mA total if
both pins are tied together.
A turn-on MUTE or soft start circuit may also be used during
power up. A simple circuit like the one shown below may be
used.
200724A3
The RC combination of C
M
and R
M1
may cause the voltage
at point A to change more slowly than the -V
EE
supply
voltage. Until the voltage at point A is low enough to have
0.5mA of current per MUTE pin flow through R
M2
, the IC will
be in mute mode. The series combination of R
M1
and R
M2
needs to satisfy the mute equation above for all operating
voltages or mute mode may be activated during normal
operation. For a longer turn-on mute time, a larger time
constant,
τ
= RC = R
C
(sec), is needed. For the values
show above and with the MUTE pins tied together, the
LM4732 will enter play mode when the voltage at point A is
-17.6V. The voltage at point A is found with Equation (1)
below.
V
A
(t) = (V
f
- V
O
)e
-t/
τ
(Volts)
where:
t = time (sec)
τ
= RC (sec)
V
o
= Voltage on C at t = 0 (Volts)
V
f
= Final voltage, -V
EE
in this circuit (Volts)
(1)
UNDER-VOLTAGE PROTECTION
Upon system power-up, the under-voltage protection cir-
cuitry allows the power supplies and their corresponding
capacitors to come up close to their full values before turning
on the LM4732. Since the supplies have essentially settled
to their final value, no DC output spikes occur. At power
down, the outputs of the LM4732 are forced to ground before
the power supply voltages fully decay preventing transients
on the output.
OVER-VOLTAGE PROTECTION
The LM4732 contains over-voltage protection circuitry that
limits the output current while also providing voltage clamp-
ing. The clamp does not, however, use internal clamping
diodes. The clamping effect is quite the same because the
output transistors are designed to work alternately by sinking
large current spikes.
THERMAL PROTECTION
The LM4732 has a sophisticated thermal protection scheme
to prevent long-term thermal stress of the device. When the
temperature on the die exceeds 150C, the LM4732 shuts
down. It starts operating again when the die temperature
drops to about 145C, but if the temperature again begins to
rise, shutdown will occur again above 150C. Therefore, the
device 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 150C and
145C. 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 so that
thermal shutdown is not activated during normal operation.
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
limiting the output power.
Equation (2)
shows the theoretical maximum power dissipa-
tion point of each amplifier in a single-ended configuration
where V
CC
is the total supply voltage.
P
DMAX
= (V
CC
)
2
/ 2
π
2
R
L
(2)
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
results from
Equation (2)
since there are two amplifiers in
each LM4732. Refer to the graphs of Power Dissipation
versus Output Power in the
Typical Performance Charac-
teristics
section which show the actual full range of power
dissipation not just the maximum theoretical point that re-
sults from
Equation (2)
.
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 is not activated under
normal circumstances.
The thermal resistance from the die to the outside air,
θ
JA
(junction to ambient), is a combination of three thermal re-
sistances,
θ
JC
(junction to case),
θ
CS
(case to sink), and
θ
SA
(sink to ambient). The thermal resistance,
θ
JC
(junction to
case), of the LM4732T is 0.8C/W. Using Thermalloy Ther-
macote thermal compound, the thermal resistance,
θ
CS
(case to sink), is about 0.2C/W. Since convection heat flow
(power dissipation) is analogous to current flow, thermal
L
www.national.com
13
相關PDF資料 |
PDF描述 |
|---|---|
| LM4732TA | Stereo 50W Audio Power Amplifier with Mute |
| LM4780 | Audio Power Amplifier Series Stereo 60W, Mono 120W Audio Power Amplifier with Mute |
| LM4780TA | Audio Power Amplifier Series Stereo 60W, Mono 120W Audio Power Amplifier with Mute |
| LM4781TA | Overture⑩ Audio Power Amplifier Series 3 Channel 35W Audio Power Amplifier with Mute |
| LM4781 | Overture⑩ Audio Power Amplifier Series 3 Channel 35W Audio Power Amplifier with Mute |
相關代理商/技術參數(shù) |
參數(shù)描述 |
|---|---|
| LM4732TA | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Stereo 50W Audio Power Amplifier with Mute |
| LM4733 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:3 Channel 30W Audio Power Amplifier with Mute |
| LM4733BG240G320WCF | 制造商:DENSITRON 功能描述:LCD MODULE GRAPHIC |
| LM4733TA | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:3 Channel 30W Audio Power Amplifier with Mute |
| LM4733TABD | 功能描述:音頻 IC 開發(fā)工具 LM4733 EVAL BOARD RoHS:否 制造商:Texas Instruments 產(chǎn)品:Evaluation Kits 類型:Audio Amplifiers 工具用于評估:TAS5614L 工作電源電壓:12 V to 38 V |
發(fā)布緊急采購，3分鐘左右您將得到回復。