Rainbow Electronics MAX98089 - Manual (Page 124)

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MAX98089
Low-Power, Stereo Audio Codec
with FlexSound Technology
Many configuration options in the ICs can be made
while the devices are operating, however, some regis-
ters should only be adjusted when the corresponding
audio path is disabled. Table 39 lists the registers that
are sensitive during operation. Either disable the cor-
responding audio path or set SHDN = 0 while changing
these registers.
Component Selection
Optional Ferrite Bead Filter
In applications where speaker leads exceed 20mm,
additional EMI suppression can be achieved by using a
filter constructed from a ferrite bead and a capacitor to
ground (Figure 42). Use a ferrite bead with low DC resis-
tance, high-frequency (> 600MHz) impedance between
100I and 600I, and rated for at least 1A. The capacitor
value varies based on the ferrite bead chosen and the
actual speaker lead length. Select a capacitor less than
1nF based on EMI performance.
Input Capacitor
An input capacitor, C IN , in conjunction with the input
impedance of the IC line inputs forms a highpass filter
that removes the DC bias from an incoming analog
signal. The AC coupling capacitor allows the amplifier
to automatically bias the signal to an optimum DC level.
Assuming zero-source impedance, the -3dB point of the
highpass filter is given by:
-3dB
IN IN
1
f
2 R C
=
π
Choose C IN so that f -3dB is well below the lowest fre-
quency of interest. For best audio quality use capacitors
whose dielectrics have low-voltage coefficients, such as
tantalum or aluminum electrolytic. Capacitors with high-
voltage coefficients, such as ceramics, may result in
increased distortion at low frequencies.
Charge-Pump Capacitor Selection
Use capacitors with an ESR less than 100mI for optimum
performance. Low-ESR ceramic capacitors minimize the
output resistance of the charge pump. Most surface-
mount ceramic capacitors satisfy the ESR requirement.
For best performance over the extended temperature
range, select capacitors with an X7R dielectric.
Table 39. Registers That Are Sensitive to Changes During Operation
Figure 42. Optional Class D Ferrite Bead Filter
MAX98089
SPK_P
SPK_N
REGISTER DESCRIPTION
0x10 to 0x13, 0x19 to 0x1B Clock Control Registers
0x14 to 0x17, 0x1C to 0x1F Digital Audio Interface Configuration
0x18, 0x20 Digital Passband Filters
0x25 to 0x2D Analog Mixers
0x52 to 0xC9 Digital Signal Processing Coefficients