TDA1400 Tripath Technology, TDA1400 Datasheet - Page 17

• Manufacturer Part Number: TDA1400
• Description: MONO CLASS-T DIGITAL AUDIO AMPLIFIER DRIVER
• Manufacturer: Tripath Technology

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Input Capacitor Selection
C
frequency pole. Typically this pole is set below 10Hz to minimize attenuation at 20Hz. C
according to:
Auxiliary Op Amp
The unused inverting op amp, as shown, is simply a voltage follower. As configured, it is not used in the
circuit. But this op amp can be used for any general purpose filtering function that requires an inverting
op amp.
Modulator Feedback Design
The modulator converts the signal from the input stage to the high-voltage output signal. The optimum
gain of the modulator is determined from the maximum allowable feedback level for the modulator and
maximum supply voltages for the power stage. Depending on the maximum supply voltage, the feedback
ratio will need to be adjusted to maximize performance. The values of R
explanation below) define the gain of the modulator. Once these values are chosen, based on the
maximum supply voltage, the gain of the modulator will be fixed.
For the best signal-to-noise ratio and lowest distortion, the modulator feedback resistors should be
adjusted to produce a differential modulator feedback voltage should be approximately 4Vpp. This will
keep the gain of the modulator as low as possible and still allow headroom so that the feedback signal
does not clip the modulator feedback stage. Sometimes increasing the value of R
to achieve full power for the amplifier since the input stage will clip at approximately 4Vpp. This will
ensure that the input stage doesn’t clip before the output stage.
Figure 3 shows how the feedback from the output of the amplifier is returned to the input of the modulator.
The input to the modulator (FBK_POS and FBK_NEG) can be viewed as inputs to an inverting differential
amplifier. R
OUTN signal to down to 4Vpp differentially.
17
I
can be calculated once a value for R
C
where: R
I
= 1 / (2π x F
FBA
and R
F
P
I
= Input resistor value in ohms (typically 20kΩ)
= Input low frequency pole (typically 3.6Hz)
FBB
Processing
Modulation
P
TDA1400
bias the feedback signal to approximately 2.5V and R
Figure 3: Modulator Feedback
x R
&
I
)
FBK_NEG
FBK_POS
I
has been determined. C
R
R
FBB
FBA
AGND
V5
R
R
FBA
FBB
T r i p a t h T e c h n o l o g y , I n c . - P r e l i m i n a r y I n f o r m a t i o n
R
R
FBC
FBC
OUTP
OUTN
I
and R
I
FBA
determine the input low-
, R
T D A 1 4 0 0 – R e v . 0 . 6 5 / K L i / 0 2 . 0 6
FBC
FBB
scales the large OUTP /
and R
FBC
may be necessary
FBC
IN
is calculated
(see