參數資料
型號: TPA0112PWPR
廠商: TEXAS INSTRUMENTS INC
元件分類: 音頻控制
英文描述: 2 CHANNEL(S), VOLUME CONTROL CIRCUIT, PDSO24
封裝: GREEN, PLASTIC, HTSSOP-24
文件頁數: 14/34頁
文件大?。?/td> 655K
代理商: TPA0112PWPR
www.ti.com
INPUT CAPACITOR, C
I
f
c(highpass) +
1
2 p Z
I
C
I
3 dB
fc
(2)
C
I +
1
2 p Z
I fc
(3)
POWER SUPPLY DECOUPLING, C
S
MIDRAIL BYPASS CAPACITOR, C
BYP
TPA0112
SLOS204C – MAY 1999 – REVISED SEPTEMBER 2004
In the typical application, an input capacitor, CI, is required to allow the amplifier to bias the input signal to the
proper dc level for optimum operation. In this case, CI and the input impedance of the amplifier, ZI, form a
high-pass filter with the corner frequency determined in Equation 2.
The value of CI is important to consider as it directly affects the bass (low-frequency) performance of the circuit.
Consider the example where ZI is 26 k and the specification calls for a flat bass response down to 65 Hz.
Equation 2 is reconfigured as Equation 3.
In this example, CI is 94 nF so one would likely choose a value in the range of 0.1 F to 1 F. A further
consideration for this capacitor is the leakage path from the input source through the input network (CI) and the
feedback network to the load. This leakage current creates a dc-offset voltage at the input to the amplifier that
reduces useful headroom, especially in high gain applications. For this reason a low-leakage tantalum or ceramic
capacitor is the best choice. When polarized capacitors are used, the positive side of the capacitor should face
the amplifier input in most applications as the dc level there is held at VDD/2, which is likely higher than the
source dc level. Note that it is important to confirm the capacitor polarity in the application.
The TPA0112 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling to
ensure that the output total harmonic distortion (THD) is as low as possible. Power supply decoupling also
prevents oscillations for long lead lengths between the amplifier and the speaker. The optimum decoupling is
achieved by using two capacitors of different types that target different types of noise on the power supply leads.
For higher frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance (ESR)
ceramic capacitor, typically 0.1 F placed as close as possible to the device VDD lead works best. For filtering
lower frequency noise signals, a larger aluminum electrolytic capacitor of 10 F or greater placed near the audio
power amplifier is recommended.
The midrail bypass capacitor, CBYP, is the most critical capacitor and serves several important functions. During
start-up or recovery from shutdown mode, CBYP determines the rate at which the amplifier starts up. 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, which appears as degraded PSRR and
THD+N.
Bypass capacitor, CBYP, values of 0.47-F to 1-F ceramic or tantalum low-ESR capacitors are recommended for
the best THD and noise performance.
21
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