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參數(shù)資料
| 型號： | LM4923 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 1.1 Watt Fully Differential Audio Power Amplifier With Shutdown Select |
| 中文描述： | 1.1瓦特全差分音頻功率放大器，具有關(guān)斷選擇 |
| 文件頁數(shù)： | 10/12頁 |
| 文件大?。?/td> | 433K |
| 代理商： | LM4923 |
Application Information
(Continued)
The via diameter should be 0.012in - 0.013in. Ensure effi-
cient thermal conductivity by plating-through and solder-
filling the vias.
Best thermal performance is achieved with the largest prac-
tical copper heat sink area. In all circumstances and condi-
tions, the junction temperature must be held below 150C to
prevent activating the LM4923’s thermal shutdown protec-
tion. The LM4923’s power de-rating curve in the Typical
Performance Characteristics shows the maximum power
dissipation versus temperature. Example PCB layouts are
shown in the Demonstration Board Layout section. Further
detailed and specific information concerning PCB layout,
fabrication, and mounting an LLP package is available from
National Semiconductor’s package Engineering Group un-
der application note AN1187.
PCB LAYOUT AND SUPPLY REGULATION
CONSIDERATIONS FOR DRIVING 4
LOADS
Power dissipated by a load is a function of the voltage swing
across the load and the load’s impedance. As load imped-
ance decreases, load dissipation becomes increasingly de-
pendent on the interconnect (PCB trace and wire) resistance
between the amplifier output pins and the load’s connec-
tions. Residual trace resistance causes a voltage drop,
which results in power dissipated in the trace and not in the
load as desired. This problem of decreased load dissipation
is exacerbated as load impedance decreases. Therefore, to
maintain the highest load dissipation and widest output volt-
age swing, PCB traces that connect the output pins to a load
must be as wide as possible.
Poor power supply regulation adversely affects maximum
output power. A poorly regulated supply’s output voltage
decreases with increasing load current. Reduced supply
voltage causes decreased headroom, output signal clipping,
and reduced output power. Even with tightly regulated sup-
plies, trace resistance creates the same effects as poor
supply regulation. Therefore, making the power supply
traces as wide as possible helps maintain full output voltage
swing.
POWER DISSIPATION
Power dissipation is a major concern when designing a
successful amplifer, whether the amplifier is bridged or
single-ended. Equation 2 states the maximum power dissi-
pation point for a single-ended amplifier operating at a given
supply voltage and driving a specified output load.
P
DMAX
= (V
DD
)
2
/ (2
π
2
R
L
) Single-Ended
(2)
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is an increase in
internal power dissipation versus a single-ended amplifier
operating at the same conditions.
P
DMAX
= 4 * (V
DD
)
2
/ (2
π
2
R
L
) Bridge Mode
(3)
Since the LM4923 has bridged outputs, the maximum inter-
nal power dissipation is 4 times that of a single-ended am-
plifier. Even with this substantial increase in power dissipa-
tion, the LM4923 does not require additional heatsinking
under most operating conditions and output loading. From
Equation 3, assuming a 5V power supply and an 8
load,
the maximum power dissipation point is 625mW. The maxi-
mum power dissipation point obtained from Equation 3 must
not be greater than the power dissipation results from Equa-
tion 4:
P
DMAX
= (T
JMAX
- T
A
) /
θ
JA
(4)
The LM4923’s
θ
JA
in an LQB08A package is 140C/W. De-
pending on the ambient temperature, T
A
, of the system
surroundings, Equation 4 can be used to find the maximum
internal power dissipation supported by the IC packaging. If
the result of Equation 3 is greater than that of Equation 4,
then either the supply voltage must be decreased, the load
impedance increased, the ambient temperature reduced, or
the
θ
reduced with heatsinking. In many cases, larger
traces near the output, V
, and GND pins can be used to
lower the
θ
. The larger areas of copper provide a form of
heatsinking allowing higher power dissipation. For the typical
application of a 5V power supply, with an 8
load, the
maximum ambient temperature possible without violating the
maximum junction temperature is approximately 62C pro-
vided that device operation is around the maximum power
dissipation point. Recall that internal power dissipation is a
function of output power. If typical operation is not around the
maximum power dissipation point, the LM4923 can operate
at higher ambient temperatures. Refer to the
Typical Per-
formance Characteristics
curves for power dissipation in-
formation.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is
critical for low noise performance and high power supply
rejection ratio (PSRR). The capacitor location on both the
bypass and power supply pins should be as close to the
device as possible. A larger half-supply bypass capacitor
improves PSRR because it increases half-supply stability.
Typical applications employ a 5V regulator with 10μF and
0.1μF bypass capacitors that increase supply stability. This,
however, does not eliminate the need for bypassing the
supply nodes of the LM4923. The LM4923 will operate with-
out the bypass capacitor C
, although the PSRR may de-
crease. A 1μF capacitor is recommended for C
. This value
maximizes PSRR performance. Lesser values may be used,
but PSRR decreases at frequencies below 1kHz. The issue
of C
selection is thus dependant upon desired PSRR and
click and pop performance as explained in the section
Proper Selection of External Components
.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4923 contains shutdown circuitry that is used to turn off
the amplifier’s bias circuitry. The device may then be placed
into shutdown mode by toggling the Shutdown Select pin to
logic low. The trigger point for shutdown is shown as a typical
value in the Supply Current vs Shutdown Voltage graphs in
the
Typical Performance Characteristics
section. It is best
to switch between ground and supply for maximum perfor-
mance. While the device may be disabled with shutdown
voltages in between ground and supply, the idle current may
be greater than the typical value of 0.1μA. In either case, the
shutdown pin should be tied to a definite voltage to avoid
unwanted state changes.
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry, which pro-
L
www.national.com
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| LM4923_07 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:1.1 Watt Fully Differential Audio Power Amplifier With Shutdown Select |
| LM4923LQ | 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(fēng)格:SMD/SMT 封裝 / 箱體:TQFP-64 封裝:Reel |
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| LM4923LQBD/NOPB | 制造商:Texas Instruments 功能描述:Evaluation Kit For 1.1 Watt Fully Differential Audio Power Amplifier With Shut-Down Select |
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