tda2075a Tripath Technology Inc., tda2075a Datasheet - Page 14

• Manufacturer Part Number: tda2075a
• Description: Stereo Class-t Digital Audio Amplifier Driver Using Digital Power Processingtm
• Manufacturer: Tripath Technology Inc.

TDA2075A Grounding
Proper grounding techniques are required to maximize TDA2075A functionality and performance.
Parametric parameters such as THD+N, Noise Floor and Crosstalk can be adversely affected if proper
grounding techniques are not implemented on the PCB layout. The following discussion highlights some
recommendations about grounding both with respect to the TDA2075A as well as general “audio system”
design rules.
The TDA2075A is divided into three sections: the input processor section, the FET driver section, and the
complementary output MOSFETs (high voltage) section. On the TDA2075A evaluation board, the ground
is also divided into distinct sections, Analog Ground (AGND) and Power Ground (PGND). To minimize
ground loops and keep the audio noise floor as low as possible, the two grounds must be only connected
at a single point.
The ground for the 5V supply is referred to as the analog ground and must be connected to pins 5, 41,
and 42 on the TDA2075A. Additionally, any external input circuitry such as preamps, or active filters,
should be referenced to the analog ground. The substrate, pin 36, should also be connected to the
analog ground.
For the power section, Tripath has traditionally used a “star” grounding scheme. Thus, the load ground
returns and the power supply decoupling traces are routed separately back to the power supply. In
addition, any type of shield or chassis connection would be 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 TDA2075A. It is possible to use a low impedance ground plane for PGND as well.
But the ground plane must be contiguous or ground currents from each channel can create crosstalk
issues. To minimize these issues, the FBKOUT1 (FBKOUT2) lines should be routed directly from the
PGND side of the load.
The TDA2075A incorporates a differential feedback system to minimize the effects of ground bounce and
cancel out common mode ground noise. Therefore, the feedback from the output ground for each
channel needs to be properly sensed. This can be accomplished by connecting the output ground
“sensing” trace directly to the star formed by the output ground return, output capacitor, C
capacitor, C
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To maximize the damping factor and reduce distortion and noise, the modulator feedback
connections should be routed directly to the pins of the output inductors. L
The output filter capacitor, C
return. The output ground feedback signal should be taken from this star point.
The modulator feedback resistors, R
together. These connections will serve to minimize common mode noise via the differential
feedback.
The feedback signals that come directly from the output inductors are high voltage and high
frequency in nature. If they are routed close to the input nodes, INV1 and INV2, the high
impedance inverting op-amp pins will pick up noise. This coupling will result in significant
background noise, especially when the input is AC coupled to ground, or an external source
such as a CD player or signal generator is connected. Thus, care should be taken such that
the feedback lines are not routed near any of the input section.
To minimize the possibility of any noise pickup, the trace lengths of INV1 and INV2 should be
kept as short as possible. This is most easily accomplished by locating the input resistors, R
and the input stage feedback resistors, R
the offset trim resistor, R
the TDA2075A input section.
Z
. Refer to the Application / Test Circuit for a schematic description.
OFB
, which connects to either INV1, or INV2, should be located close to
O
, and zobel capacitor, C
FBA
and R
F
as close to the TDA2075A as possible. In addition,
FBB
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
, should all be grounded and attached to 5V
Z
, should be star connected with the load
T D A 2 0 7 5 A – R e v . 0 . 9 / K L i / 1 0 . 0 5
O
.
O
, and the zobel
I