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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： | 14/18页 |
| 文件大小： | 648K |
| 代理商： | TC4864EUAG |
2001 Microchip Technology Inc.
DS21483
TC4864
300mW Audio Power Amplifier with Shutdown Mode
TC4864-1 12/20/00
RM
Power Supply Bypassing
As with any power amplifier, proper supply bypassing is
essential for low noise performance and high power supply
rejection. The location of the capacitor on both the bypass
and power supply pins should be as near the device as
possible. A larger half supply bypass capacitor has the effect
of improved PSRR due to increased half-supply stability.
Typical applications use a 5V regulator with 10
F and a
0.1
F bypass capacitor which aids in supply stability, but
does not eliminate the need for bypassing the supply nodes
of the TC4864. The selection of bypass capacitors, espe-
cially CB, is thus dependent upon desired PSRR require-
ments, click and pop performance (as explained in the
Proper Selection of External Components section), sys-
tem cost, and size limitations.
Shutdown Function
The TC4864 contains a shutdown pin to externally turn
off the amplifier’s bias circuitry in order to reduce power
consumption while not in use. This feature turns the amplifier
off when a logic high is placed on the shutdown pin. Typi-
cally, half supply is the trigger point between a logic low and
logic high level. To provide maximum device performance,
it's best to switch between the VIL and VIH limits specified in
the Electrical Characteristics tables. By switching the shut-
down pin to VDD, the TC4864 supply current draw will be
minimized in the shutdown mode. While the device may be
disabled with shutdown pin voltages less than the minimum
VIH, the shutdown current may be greater than the typical
value of 0.1
A. Regardless of the conditions, the shutdown
pin should be tied to a definite voltage so as to avoid
unwanted state changes.
In many applications, a microcontroller or microproces-
sor output is used to control the shutdown circuitry which
provides a quick, smooth transition into shutdown. Another
solution is to use a single-pole, single-throw switch in tan-
dem with an external pull-up resistor. When the switch is
closed, the shutdown pin is connected to ground and en-
ables the amplifier. Conversely, if the switch is open, the
external pull-up resistor will disable the TC4864. This design
ensures that the shutdown pin will not float, thus preventing
undesireable state changes.
Proper Selection of External Components
Proper selection of external components in applications
employing integrated power amplifiers is crucial in optimiz-
ing device and system performance. While the TC4864 is
tolerant of a variety of external component combinations,
consideration must be given to component values in order to
maximize overall system quality.
The TC4864 is unity-gain stable, giving maximum sys-
tem flexibility to the designer. The TC4864 is best used in low
gain configurations to minimize THD+N values and maxi-
mize the signal to noise ratio. Low gain configurations
require large input signals to obtain a specified output
power. Audio CODECs are sources from which input signals
equal to or greater than 1 VRMS are available. For a more
complete explanation of proper gain selection please refer
to the section, Audio Power Amplifier Design.
In addition to gain, one of the major considerations is the
closed-loop bandwidth of the amplifier. The bandwidth is
dictated, to a large extent, by the choice of external compo-
nents shown in Figure 1. The input coupling capacitor, Ci ,
forms a first order high pass filter which limits low frequency
response. This value should be chosen based on needed
frequency response for a few distinct reasons.
Selection of Input Capacitor Size
Large input capacitors are too bulky and less cost
effective for portable designs. There is clearly a need for a
space-saving capacitor to couple in low frequencies without
drastic attenuation. But, in many cases, the speakers used
in portable systems, whether internal or external, lack the
ability to reproduce signals below 150Hz. In this specific
case, employing a large input capacitor may not increase
system performance.
In addition to system cost and size, click and pop perfor-
mance is effected by the size of the input coupling capacitor,
Ci. A larger input coupling capacitor requires more charge
to reach its inactive DC voltage (nominally 1/2 VDD ). This
charge comes from the output via the feedback and is apt to
create pops upon enabling the device. Thus, by minimizing
the capacitor size based on necessary low frequency re-
sponse, turn-on pops are minimized.
Besides minimizing the input capacitor size, careful
attention should be paid to the bypass capacitor value.
Bypass capacitor,CB is the most critical component in mini-
mizing turn-on pops, since it determines how fast the TC4864
turns on. The slower the TC4864’s outputs ramp to their
quiescent DC voltage (nominally 1/ 2 VDD ), the smaller the
turn-on pop. Choosing CB = 1.0F along with a small value
of Ci (in the range of 0.1F to 0.39F), should produce a
clickless and popless shutdown function. While the device
will function properly (no oscillations or motorboating) with
CB = 0.1F , the device will be much more susceptible to
turn-on clicks and pops. Thus, a value of CB = 1.0F or larger
is recommended in all but the most cost sensitive designs.
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