Rainbow Electronics MAX98302 - Manual (Page 9)

_______________________________________________________________________________________ 9
MAX98302
Stereo 2.4W Class D Amplifier
Input Filtering
The input-coupling capacitor (C IN ), in conjunction with
the amplifier’s internal input resistance (R IN ), forms a
highpass filter that removes the DC bias from the incom-
ing signal. These capacitors allow the amplifier to bias
the signal to an optimum DC level.
Assuming zero-source impedance with a gain setting of
A
V = 12dB, 15dB, or 18dB, C IN is:
IN
3dB
8
C [ F]
f
−
= µ
with a gain setting of A
V
= 9dB, C
IN
is:
IN
3dB
5.7
C [ F]
f
−
= µ
with a gain setting of A V = 6dB, C IN is:
IN
3dB
4
C [ F]
f
−
= µ
where f -3dB is the -3dB corner frequency. Use capaci-
tors with adequately low-voltage coefficients for best
low-frequency THD performance.
Layout and Grounding
Proper layout and grounding are essential for optimum
performance. Good grounding improves audio perfor-
mance and prevents switching noise from coupling into
the audio signal.
Use wide, low-resistance output traces. As load imped-
ance decreases, the current drawn from the device
outputs increase. At higher current, the resistance of
the output traces decrease the power delivered to the
load. For example, if 2W is delivered from the speaker
output to a 4I load through a 100mI trace, 49mW is
consumed in the trace. If power is delivered through a
10mI trace, only 5mW is consumed in the trace. Wide
output, supply, and ground traces also improve the
power dissipation of the device.
The MAX98302 is inherently designed for excellent RF
immunity. For best performance, add ground fills around
all signal traces on top or bottom PCB planes.
The MAX98302 TDFN-EP package features an exposed
thermal pad on its underside. This pad lowers the pack-
age’s thermal resistance by providing a heat conduction
path from the die to the PCB. Connect the exposed
thermal pad to the ground plane by using a large pad
and multiple vias.