Datasheet

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−
+
R
I
R
O
R
L
V
I
Too Long
Too Long
Too Long
Too Long
TPA6120A2
R
F
−
+
R
I
R
O
R
L
V
I
TPA6120A2
Ground as Close to
the Pin as Possible
Short Trace
Before Resistors
R
F
Minimized Length of
the Trace Between
Output Node and R
O
Minimized Length of
Feedback Path
Thermal Considerations
Efficiency of an amplifier 
P
L
P
SUP
(1)
P
L

V
LRMS
2
R
L
, and V
LRMS

V
P
2

, therefore, P
L

V
P
2
2R
L
per channel
(2)
P
SUP
 V
CC
I
CC
avg  V
CC
I
CC(q)
(3)
I
CC
avg

1



2
0
V
P
R
L
sin(t) dt  
V
P
R
L
[cos(t)]

2
0

V
P
 R
L
(4)
TPA6120A2
SLOS431 – MARCH 2004
APPLICATION INFORMATION (continued)
Despite the removal of the ground plane in critical areas, stray capacitance can still make its way onto the
sensitive outputs and inputs. Place components as close as possible to the pins and reduce trace lengths. See
Figure 33 and Figure 34 . It is important for the feedback resistor to be extremely close to the pins, as well as the
series output resistor. The input resistor should also be placed close to the pin. If the amplifier is to be driven in a
noninverting configuration, ground the input close to the device so the current has a short, straight path to the
PowerPAD (gnd).
Figure 33. Layout That Can Cause Oscillation
Figure 34. Layout Designed To Reduce Capacitance On Critical Nodes
Amplifiers can generate quite a bit of heat. Linear amplifiers, as opposed to Class-D amplifiers, are extremely
inefficient, and heat dissipation can be a problem. There is no one to one relationship between output power and
heat dissipation, so the following equations must be used:
Where
Where
17