tda2500 Tripath Technology Inc., tda2500 Datasheet - Page 16

• Manufacturer Part Number: tda2500
• Description: Stereo Class-t Digital Audio Amplifier Driver Using Digital Power Processing Dpp
• Manufacturer: Tripath Technology Inc.

IN PUT CAPAC ITOR SELECTION
C
frequency pole. Typically this pole is set at 10Hz. C
MODULA TOR FEEDBACK D ESIGN
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 value of R
internal to the TDA2500 hybrid, (see 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 even as
the supply voltage fluctuates due to current draw.
For the best signal-to-noise ratio and lowest distortion, the maximum modulator feedback voltage should
be approximately 4.5Vpp. 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. It should be noted that
the modulator works over basically a 2:1 supply voltage ratio with optimum performance around 3.5Vpp-
4Vpp of feedback. Thus, the actual value of R
shown in the Application/Test Circuit to achieve maximum performance.
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 (FDBKN1/GNDKELVIN1 for channel 1) can be viewed as inputs to an inverting
differential amplifier. The internal 1k: and 1.02k: resistors bias the feedback signal to approximately
2.5V and R
4Vpp, depending on the supply voltage, VPP and VNN.
16
I
can be calculated once a value for R
C
where: R
I
= 1 / (2S x F
FB
, along with the internal series 1k:, scales the large output1 signal to down to approximately
F
P
I
= Input resistor value in ohms
= Input low frequency pole (typically less than 10Hz)
P
Figure 3: Modulator Feedback
x R
Processing
Modulation
I
)
&
1/2 TDA2500
1.02K
1.02K
AGND
V5
IN
1.02K
1.02K
has been determined. C
1.0K
1.0K
FB
may need to be adjusted from the typical value (39.2k:)
GNDKELVIN1
I
is calculated according to:
FDBKN1
T r i p a t h T e c h n o l o g y , I n c . - T e c h n i c a l I n f o r m a t i o n
18
9
18.7K 1/4W
18.7K 1/4W
I
and R
TDA2500 – KL/ Rev. 0.9/05.05
FB
, in conjunction with resistors
OUTPUT 1
OUTPUT 1
GROUND
I
determine the input low-