MAX9888 Maxim Integrated Products, MAX9888 Datasheet - Page 109

• Manufacturer Part Number: MAX9888
• Description: Stereo Audio CODEC
• Manufacturer: Maxim Integrated Products

DataSheet.in
Traditional Class D amplifiers require an output filter
to recover the audio signal from the amplifier’s output.
The filters add cost, increase the solution size of the
amplifier, and can decrease efficiency and THD+N
performance. The traditional PWM scheme uses large
differential output swings (2 x V
causes large ripple currents. Any parasitic resistance in
the filter components results in a loss of power, lowering
the efficiency.
The IC does not require an output filter. The device relies
on the inherent inductance of the speaker coil and the
natural filtering of both the speaker and the human ear
to recover the audio component of the square-wave out-
put. Eliminating the output filter results in a smaller, less
costly, more efficient solution.
Because the frequency of the IC output is well beyond
the bandwidth of most speakers, voice coil move-
ment due to the square-wave frequency is very small.
Although this movement is small, a speaker not designed
to handle the additional power can be damaged. For
optimum results, use a speaker with a series inductance
> 10FH. Typical 8I speakers exhibit series inductances
in the 20FH to 100FH range.
GSM radios transmit using time-division multiple access
(TDMA) with 217Hz intervals. The result is an RF signal
with strong amplitude modulation at 217Hz and its har-
monics that is easily demodulated by audio amplifiers.
The IC is designed specifically to reject RF signals; how-
ever, PCB layout has a large impact on the susceptibility
of the end product.
Table 39. Example Startup Sequence
SEQUENCE
10
1
2
3
4
5
6
7
8
9
Ensure SHDN = 0
Configure clocks
Configure digital audio interface
Configure digital signal processing
Load coefficients
Configure mixers
Configure gain and volume controls
Configure miscellaneous functions
Enable desired functions
Set SHDN = 1
Filterless Class D Operation
DD
RF Susceptibility
peak to peak) and
DESCRIPTION
with FLEXSOUND Technology
In RF applications, improvements to both layout and com-
ponent selection decrease the IC’s susceptibility to RF
noise and prevent RF signals from being demodulated into
audible noise. Trace lengths should be kept below 1/4 of
the wavelength of the RF frequency of interest. Minimizing
the trace lengths prevents them from functioning as anten-
nas and coupling RF signals into the IC. The wavelength
(l) in meters is given by: l = c/f where c = 3 x 10
f = the RF frequency of interest.
Route audio signals on middle layers of the PCB to allow
ground planes above and below to shield them from RF
interference. Ideally, the top and bottom layers of the
PCB should primarily be ground planes to create effec-
tive shielding.
Additional RF immunity can also be obtained by rely-
ing on the self-resonant frequency of capacitors as it
exhibits a frequency response similar to a notch filter.
Depending on the manufacturer, 10pF to 20pF capaci-
tors typically exhibit self resonance at the RF frequencies
of interest. These capacitors, when placed at the input
pins, can effectively shunt the RF noise to ground. For
these capacitors to be effective, they must have a low-
impedance, low-inductance path to the ground plane.
Avoid using microvias to connect to the ground plane
whenever possible as these vias do not conduct well at
RF frequencies.
To ensure proper device initialization and minimal click-
and-pop, program the IC’s SHDN = 1 after configuring all
registers. Table 39 lists an example startup sequence for
the device. To shut down the IC, simply set SHDN = 0.
Stereo Audio CODEC
Startup/Shutdown Sequencing
0x4C
0x10 to 0x13, 0x19 to 0x1B
0x14 to 0x17, 0x1C to 0x1F
0x18, 0x20, 0x3D to 0x44
0x50 to 0xC7
0x21 to 0x29
0x2A to 0x3C
0x45 to 0x49
0x4A, 0x4B
0x4C
REGISTERS
8
m/s, and
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