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参数资料
| 型号： | TC4864EUAG |
| 元件分类： | 音频／视频放大 |
| 英文描述： | 0.74 W, 1 CHANNEL, AUDIO AMPLIFIER, PDSO8 |
| 封装： | MSOP-8 |
| 文件页数： | 13/18页 |
| 文件大小： | 648K |
| 代理商： | TC4864EUAG |
TC4864
4
TC4864-1 12/20/00
300mW Audio Power Amplifier with Shutdown Mode
2001 Microchip Technology Inc.
DS21483A
DETAILED DESCRIPTION
Application Information
Bridge Configuration Explanation
As shown in Figure 1, the TC4864 has two operational
amplifiers internally, allowing for several different amplifier
configurations.
The first amplifier’s gain is externally configurable, while
the second amplifier is internally fixed in a unity-gain, invert-
ing configuration. The closed-loop gain of the first amplifier
is set by selecting the ratio of RF to Ri while the second
amplifier’s gain is fixed by the two internal 10k
resistors.
Figure 1 shows that the output of amplifier one serves as the
input to amplifier two which results in both amplifiers produc-
ing signals identical in magnitude, but out of phase 180
°.Con-
sequently, the differential gain for the IC is
AVD = 2*(RF/Ri)
The load is driven differentially through outputs VO1 and
VO2, creating an amplifier configuration commonly referred
to as a "bridged mode". Bridged mode operation is different
from the classical single-ended amplifier configuration where
one side of its load is connected to ground.
There are several distinct advantages to having a bridge
amplifier design as opposed to a single-ended configura-
tion. First, the bridge design provides differential drive to the
load, thus doubling output swing for a predetermined supply
voltage. Second, it is possible to generate four times the
output power as that of a single-ended amplifier under the
same conditions, provided that the amplifier is not current
limited or clipped. For information on how to choose an
amplifier’s closed-loop gain while avoiding excessive clip-
ping, please refer to the Audio Power Amplifier Design
section.
A bridge configuration, such as the one used in the
TC4864, also creates a third advantage over single-ended
amplifiers. Since the differential outputs, VO1 and VO2 , are
biased at half-supply, no net DC voltage exists across the
load. Thus, the need for an output coupling capacitor is
eliminated in a bridge. As opposed to a single supply, single-
ended amplifier configuration, in which the capacitor is a
requirement. 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 dissi-
pation as well as permanent loudspeaker damage.
POWER DISSIPATION
Power dissipation is an important factor when designing
a successful amplifier, whether the amplifier be bridged or
single-ended. Equation 1 illustrates the maximum power
dissipation point for a bridge amplifier operating at a given
supply voltage and driving a specified output load.
PDMAX = (VDD )
2/(2
π2RL )
Single-Ended
Equation 1.
However, a direct consequence of the increased power
delivered to the load by a bridge amplifier is an increase in
internal power dissipation point for a bridge amplifier oper-
ating under the same conditions.
PDMAX = 4(VDD )
2/(
π2RL )
Bridge Mode
Equation 2.
Since the TC4864 has two operational amplifiers in one
package, the maximum internal power dissipation is 4 times
that of a single-ended amplifier. Still, the TC4864 does not
require heatsinking, even with this substantial increase in
power dissipation, . 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
dissipation that results from Equation 3:
PDMAX = (TJMAX – TA )/θJA
Equation 3.
For the MSOP package,
θJA = 210°C/W. TJMAX = 150°C
for the TC4864. Depending on the ambient temperature, TA,
of the system surroundings, Equation 3 can be used to find
the maximum internal power dissipation supported by the IC
packaging. If the result of Equation 2 is greater than that of
Equation 3, either the supply voltage must be decreased,
the load impedance must be increased, the ambient tem-
perature reduced, or, through heat-sinking, the
θJA must be
lowered.
In a lot of cases, larger traces near the output, VDD ,and
GND pins can be used to lower the
θJA . The larger areas of
copper serve as 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 exceeding the maximum junction tempera-
ture, is approximately 44
°C. (Provided that the device op-
eration is around the maximum power dissipation point and
assuming surface mount packaging.) Internal power dissi-
pation is a function of output power. If typical operation is not
around the maximum power dissipation point, the ambient
temperature can be increased. For power dissipation infor-
mation for lower output powers, refer to the Typical Perfor-
mance Characteristics curves.
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