Tripath Technology, Inc. - Preliminary Information
connected directly to the ground star located at the power supply. These precautions will both minimize
audible noise and enhance the crosstalk performance of the TDA1400.
TDA1400 Amplifier Gain
The gain of the TDA1400 is the product of the input stage gain and the modulator gain for the TDA1400.
Please refer to the sections, Input Stage Design, and Modulator Feedback Design, for a complete
explanation of how to determine the external component values.
A V TDA1400 = A V INPUTSTAGE * A V MODULATOR
R
R
F
I
RFBC * (RFBA + RFBB )
A V TDA1400 ≈ −
+ 1
R
FBA * RFBB
For example, using a TDA1400 with the following external components,
RI = 20kΩ
RF = 20kΩ
R
FBA = 2.21kΩ
RFBB = 1kΩ
RFBC = 20kΩ
20k Ω 20.0k Ω * (1.0k Ω + 2.21k Ω)
V
V
A V TDA1400 ≈ −
+ 1 = - 30.05
20k Ω
1.0k Ω * 2.21k Ω
Input Stage Design
The TDA1400 input stage is configured as an inverting amplifier, allowing the system designer flexibility in
setting the input stage gain and frequency response. Figure 2 shows a typical application where the input
stage is a constant gain inverting amplifier. The input stage gain should be set so that the maximum input
signal level will drive the input stage output to 4Vpp.
The gain of the input stage, above the low frequency high pass filter point, is that of a simple inverting
amplifier:
R
R
F
A V INPUTSTAGE = −
I
TDA1400
OAOUT_AMP
45
V5
CI
RF
RI
INV_AMP 46
+
-
+
INPUT1
AGND
BIASCAP
V5
+
-
2
1
INV_AUX
AGND
OAOUT_AUX
Figure 2: TDA1400 Input Stage
16
TDA1400 – Rev. 0.65/KLi/02.06
TRIPATH [ TRIPATH TECHNOLOGY INC. ]
