參數資料
型號: TPA0312PWPR
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: 11/36頁
文件大?。?/td> 791K
代理商: TPA0312PWPR
www.ti.com
GAIN SETTING VIA GAIN0 AND GAIN1 INPUTS
INPUT RESISTANCE
C
R
IN
ZI
ZF
Input
Signal
–3 dB +
1
2p C R
RI
(1)
INPUT CAPACITOR, C
I
TPA0312
SLOS335A – DECEMBER 2000 – REVISED OCTOBER 2004
The gain of the TPA0312 is set by two input terminals, GAIN0 and GAIN1.
Table 1. GAIN SETTINGS
GAIN0
GAIN1
SE/BTL
AV
0
6 dB
0
1
0
10 dB
1
0
15.6 dB
1
0
X
1
4.1 dB
The gains listed in Table 1 are realized by changing the taps on the input resistors inside the amplifier. This
causes the input impedance, ZI, to be dependant on the gain setting. The actual gain settings are controlled by
ratios of resistors, so the actual gain distribution from part-to-part is quite good. However, the input impedance
will shift by 30% due to shifts in the actual resistance of the input impedance.
For design purposes, the input network (discussed in the next section) should be designed assuming an input
impedance of 10 k
, which is the absolute minimum input impedance of the TPA0312. At the lower gain settings,
the input impedance could increase as high as 115 k
.
Each gain setting is achieved by varying the input resistance of the amplifier, which can range from its smallest
value to over 6 times that value. As a result, if a single capacitor is used in the input high pass filter, the –3-dB or
cutoff frequency also changes by over 6 times. If an additional resistor is connected from the input pin of the
amplifier to ground, as shown in the following figure, the variation of the cutoff frequency is much reduced.
The typical input impedance at each gain setting is given in the table below:
Av
ZI
21.6 dB
25 k
15.6 dB
45 k
10 dB
70 k
6 dB
90 k
The –3-dB frequency can be calculated using Equation 1:
If the filter must be more accurate, the value of the capacitor should be increased while the value of the resistor
to ground should be decreased. In addition, the order of the filter could be increased.
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.
19
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