Datasheet

LM4941, LM4941SDBD, LM4941TMBD
www.ti.com SNAS347C –JUNE 2006–REVISED MAY 2013
When using DC coupled inputs, special care must be taken to match the values of the input resistors (R
i1
and
R
i2
) to each other. Because of the balanced nature of differential amplifiers, resistor matching differences can
result in net DC currents across the load. This DC current can increase power consumption, internal IC power
dissipation, reduce PSRR, and possibly damaging the loudspeaker. The chart below demonstrates this problem
by showing the effects of differing values between the feedback resistors while assuming that the input resistors
are perfectly matched. The results below apply to the application circuit shown in Figure 1, and assumes that V
DD
= 5V, R
L
= 8Ω, and the system has DC coupled inputs tied to ground.
Tolerance R
i1
R
i2
V
01
–V
02
I
LOAD
20% 0.8R 1.2R –0.500V 62.5mA
10% 0.9R 1.1R –0.250V 31.25mA
5% 0.95R 1.05R –0.125V 15.63mA
1% 0.99R 1.01R –0.025V 3.125mA
0% R R 0 0
Since the same variations can have a significant effect on PSRR and CMRR performance, it is highly
recommended that the input resistors be matched to 1% tolerance or better for best performance.
Recommended TM Board Layout
Figure 21. Recommended TM Board Layout: Top Figure 22. Recommended TM Board Layout: Top
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