参数资料
型号: TPA4861DRG4
厂商: TEXAS INSTRUMENTS INC
元件分类: 音频/视频放大
英文描述: 1.1 W, 1 CHANNEL, AUDIO AMPLIFIER, PDSO8
封装: GREEN, PLASTIC, MS-012AA, SOIC-8
文件页数: 8/26页
文件大小: 623K
代理商: TPA4861DRG4
www.ti.com
SELECTION OF COMPONENTS
Audio
Input
Bias
Control
VDD = 5 V
1-W
Internal
Speaker
6
5
8
7
VO1
VO2
VDD
1
2
3
4
IN +
IN
BYPASS
SHUTDOWN (see Note A)
VDD/2
CI
RI
RF
CF
50 k
50 k
46 k
46 k
CB
CS
NOTE A: SHUTDOWN must be held low for normal operation and asserted high for shutdown mode.
+
+
Gain Setting Resistors, RF and RI
Gain + * 2
R
F
R
I
(5)
Effective Impedance +
R
FRI
R
F ) RI
(6)
TPA4861
SLOS163C – SEPTEMBER 1996 – REVISED JUNE 2004
Figure 37 is a schematic diagram of a typical notebook computer application circuit.
Figure 37. TPA4861 Typical Notebook Computer Application Circuit
The gain for the TPA4861 is set by resistors RF and RI according to Equation 5.
BTL mode operation brings about the factor of 2 in the gain equation due to the inverting amplifier mirroring the
voltage swing across the load. Given that the TPA4861 is a MOS amplifier, the input impedance is high;
consequently, input leakage currents are not generally a concern, although noise in the circuit increases as the
value of RF increases. In addition, a certain range of RF values are required for proper start-up operation of the
amplifier. Taken together, it is recommended that the effective impedance seen by the inverting node of the
amplifier be set between 5 k
and 20 k. The effective impedance is calculated in Equation 6.
As an example, consider an input resistance of 10 k
and a feedback resistor of 50 k. The gain of the amplifier
would be –10 V/V, and the effective impedance at the inverting terminal would be 8.3 k
, which is well within the
recommended range.
For high-performance applications, metal film resistors are recommended because they tend to have lower noise
levels than carbon resistors. For values of RF above 50 k, the amplifier tends to become unstable due to a pole
formed from RF and the inherent input capacitance of the MOS input structure. For this reason, a small
compensation capacitor of approximately 5 pF should be placed in parallel with RF. This, in effect, creates a
low-pass filter network with the cutoff frequency defined in Equation 7.
16
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