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參數(shù)資料
| 型號： | LM4864N |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 音頻／視頻放大 |
| 英文描述： | 300 mW Audio Power Amplifier with Shutdown Mode |
| 中文描述： | 0.675 W, 1 CHANNEL, AUDIO AMPLIFIER, PDIP8 |
| 封裝： | 0.300 INCH, MDIP-8 |
| 文件頁數(shù)： | 7/10頁 |
| 文件大?。?/td> | 342K |
| 代理商： | LM4864N |
Application Information
BRIDGE CONFIGURATION EXPLANATION
As shown in Figure 1 the LM4864 has two operational am-
plifiers internally, allowing for a few different amplifier con-
figurations. The first amplifier’s gain is externally config-
urable, while the second amplifier is internally fixed in a
unity-gain, inverting configuration. The closed-loop gain of
the first amplifier is set by selecting the ratio of R
to R
while
the second amplifier’s gain is fixed by the two internal 10 k
resistors. Figure 1 shows that the output of amplifier one
serves as the input to amplifier two which results in both am-
plifiers producing signals identical in magnitude, but out of
phase 180. Consequently, the differential gain for the IC is
A
VD
= 2
*
(R
F
/R
i
)
By driving the load differentially through outputs V
and V
,
an amplifier configuration commonly referred to as “bridged
mode” is established. Bridged mode operation is different
from the classical single-ended amplifier configuration where
one side of its load is connected to ground.
A bridge amplifier design has a few distinct advantages over
the single-ended configuration, as it provides differential
drive to the load, thus doubling output swing for a specified
supply voltage. Four times the output power is possible as
compared to a single-ended amplifier under the same condi-
tions. This increase in attainable output power assumes that
the amplifier is not current limited or clipped. In order to
choose an amplifier’s closed-loop gain without causing ex-
cessive clipping, please refer to the
Audio Power Amplifier
Design
section.
A bridge configuration, such as the one used in LM4864,
also creates a second advantage over single-ended amplifi-
ers. Since the differential outputs, V
and V
, are biased at
half-supply, no net DC voltage exists across the load. This
eliminates the need for an output coupling capacitor which is
required in a single supply, single-ended amplifier configura-
tion. If an output coupling capacitor is not used in a
single-ended configuration, the half-supply bias across the
load would result in both increased internal lC power dissipa-
tion as well as permanent loudspeaker damage.
POWER DISSIPATION
Power dissipation is a major concern when designing a suc-
cessful amplifier, whether the amplifier is bridged or
single-ended. Equation 1 states the maximum power dissi-
pation point for a bridge amplifier operating at a given supply
voltage and driving a specified output load.
P
DMAX
= (V
DD
)
2
/(2
π
2
R
L
)
However, a direct consequence of the increased power de-
livered to the load by a bridge amplifier is an increase in in-
ternal power dissipation point for a bridge amplifier operating
at the same conditions.
P
DMAX
= 4(V
DD
)
2
/(
π
2
R
L
)
Since the LM4864 has two operational amplifiers in one
package, the maximum internal power dissipation is 4 times
that of a single-ended amplifier. Even with this substantial in-
crease in power dissipation, the LM4864 does not require
heatsinking. From Equation 1, assuming a 5V power supply
and an 8
load, the maximum power dissipation point is
625 mW. The maximum power dissipation point obtained
from Equation 2 must not be greater than the power dissipa-
tion that results from Equation 3:
P
DMAX
= (T
JMAX
T
A
)/
θ
JA
Single-Ended (1)
Bridge Mode (2)
(3)
For package MUA08A,
θ
= 210C/W, for package M08A,
θ
JA
= 170C/W and for package N08E,
θ
= 107C/W.
T
= 150C for the LM4864. Depending on the ambient
temperature, T
, of the system surroundings, Equation 3 can
be used to find the maximum internal power dissipation sup-
ported by the IC packaging. If the result of Equation 2 is
greater than that of Equation 3, then either the supply volt-
age must be decreased, the load impedance increased, the
ambient temperature reduced, or the
θ
reduced with heat-
sinking. 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 a 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 44C provided that device operation is
around the maximum power dissipation point and assuming
surface mount packaging. Internal power dissipation is a
function of output power. If typical operation is not around the
maximum power dissipation point, the ambient temperature
can be increased. Refer to the
Typical Performance Char-
acteristics
curves for power dissipation information for
lower output powers.
POWER SUPPLY BYPASSING
As with any power amplifier, proper supply bypassing is criti-
cal for low noise performance and high power supply rejec-
tion. The capacitor location on both the bypass and power
supply pins should be as close to the device as possible. The
effect of a larger half supply bypass capacitor is improved
PSRR due to increased half-supply stability. Typical applica-
tions employ a 5V regulator with 10 μF and a 0.1 μF bypass
capacitors which aid in supply stability, but do not eliminate
the need for bypassing the supply nodes of the LM4864. The
selection of bypass capacitors, especially C
, is thus depen-
dent upon desired PSRR requirements, click and pop perfor-
mance as explained in the section,
Proper Selection of Ex-
ternal Components
, system cost, and size constraints.
SHUTDOWN FUNCTION
In order to reduce power consumption while not in use, the
LM4864 contains a shutdown pin to externally turn off the
amplifier’s bias circuitry. This shutdown feature turns the am-
plifier off when a logic high is placed on the shutdown pin.
The trigger point between a logic low and logic high level is
typically half supply. It is best to switch between ground and
supply to provide maximum device performance. By switch-
ing the shutdown pin to V
, the LM4864 supply current
draw will be minimized in idle mode. While the device will be
disabled with shutdown pin voltages less than V
, the idle
current may be greater than the typical value of 0.7 μA. In ei-
ther case, the shutdown pin should be tied to a definite volt-
age to avoid unwanted state changes.
In many applications, a microcontroller or microprocessor
output is used to control the shutdown circuitry which pro-
vides a quick, smooth transition into shutdown.Another solu-
tion is to use a single-pole, single-throw switch in conjunction
with an external pull-up resistor. When the switch is closed,
the shutdown pin is connected to ground and enables the
amplifier. If the switch is open, then the external pull-up re-
sistor will disable the LM4864. This scheme guarantees that
the shutdown pin will not float, thus preventing unwanted
state changes.
www.national.com
7
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| LM4865IBPX | 功能描述:IC AMP AUDIO PWR 1W MONO 8USMD 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(biāo)準(zhǔn)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(fù)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(hù)，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) |
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