參數(shù)資料
型號(hào)： TPA112DGNG4
廠商： TEXAS INSTRUMENTS INC
元件分類(lèi)： 音頻／視頻放大
英文描述： 0.07 W, 2 CHANNEL, AUDIO AMPLIFIER, PDSO8
封裝： GREEN, PLASTIC, MSOP-8
文件頁(yè)數(shù)： 14/29頁(yè)
文件大?。?/td> 707K
代理商： TPA112DGNG4
www.ti.com
1
C
B
R
SOURCE
v
1
C
I RI
1
R
LCC
(6)
MIDRAIL BYPASS CAPACITOR, CB
1
C
B
R
SOURCE
v
1
C
I RI
(7)
6.25 v 50
(8)
OUTPUT COUPLING CAPACITOR, CC
f
(out high) +
1
2p R
L CC
(9)
TPA112
SLOS212E – AUGUST 1998 – REVISED JUNE 2004
APPLICATION INFORMATION (continued)
Where CBYPASS is the value of the bypass capacitor, and RSOURCE is the equivalent source impedance of the
voltage divider (the parallel combination of the two resistors). For example, if the voltage divider is constructed
using two 20-k
resistors, then R
SOURCE is 10 k.
The midrail bypass capacitor CB serves several important functions. During start-up, CB determines the rate at
which the amplifier starts up. This helps to push the start-up pop noise into the subaudible range (so slow it can
not be heard). The second function is to reduce noise produced by the power supply caused by coupling into the
output drive signal. This noise is from the midrail generation circuit internal to the amplifier. The capacitor is fed
from the resistor divider with equivalent resistance of RSOURCE. To keep the start-up pop as low as possible, the
relationship shown in Equation 7 should be maintained.
As an example, consider a circuit where CB is 1 F, RSOURCE = 160 k, CI is 1 F, and RI is 20 k. Inserting
these values into the Equation 8 results in:
which satisfies the rule. Recommended values for bypass capacitor CB are 0.1 F to 1 F, ceramic or tantalum
low-ESR, for the best THD and noise performance.
In the typical single-supply, single-ended (SE) configuration, an output coupling capacitor (CC) is required to
block the dc bias at the output of the amplifier, thus preventing dc currents in the load. As with the input coupling
capacitor, the output coupling capacitor and impedance of the load form a high-pass filter governed by
Equation 9.
The main disadvantage, from a performance standpoint, is that the typically small load impedances drive the
low-frequency corner higher. Large values of CC are required to pass low frequencies into the load. Consider the
example where a CC of 68 F is chosen and loads vary from 32 to 47 k. Table 1 summarizes the frequency
response characteristics of each configuration.
Table 1. Common Load Impedances vs Low Frequency
Output Characteristics in SE Mode
RL
CC
LOWEST FREQUENCY
32
68 F
73 Hz
10,000
68 F
0.23 Hz
47,000
68 F
0.05 Hz
As Table 1 indicates, headphone response is adequate and drive into line level inputs (a home stereo for
example) is good.
The output coupling capacitor required in single-supply, SE mode also places additional constraints on the
selection of other components in the amplifier circuit. With the rules described earlier still valid, add the following
relationship:
Output Pulldown Resistor, RC + RO
– Placing a 100-
resistor, R
C, from the output side of the coupling capacitor to ground ensures the coupling
capacitor, CC, is charged before a plug is inserted into the jack. Without this resistor, the coupling capacitor
would charge rapidly upon insertion of a plug, leading to an audible pop in the headphones.
21
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