MAX9879 Maxim Integrated Products, MAX9879 Datasheet - Page 29

• Manufacturer Part Number: MAX9879
• Description: Stereo Class D Audio Subsystem
• Manufacturer: Maxim Integrated Products

www.datasheet4u.com
GSM radios transmit using time-division multiple access
(TDMA) with 217Hz intervals. The result is an RF signal
with strong amplitude modulation at 217Hz that is easily
demodulated by audio amplifiers. Figure 14 shows the
susceptibility of the MAX9879 to a transmitting GSM
radio placed in close proximity. Although there is mea-
surable noise at 217Hz and its harmonics, the noise is
well below the threshold of hearing using typical head-
phones.
In RF applications, improvements to both layout and
component selection decreases the MAX9879’s sus-
ceptibility to RF noise and prevent RF signals from
being demodulated into audible noise. Trace lengths
should be kept below
quency of interest. Minimizing the trace lengths pre-
vents them from functioning as antennas and coupling
RF signals into the MAX9879. The wavelength λ in
meters is given by:
where c = 3 x 10
interest.
Route audio signals on middle layers of the PCB to
allow ground planes above and below 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 from rely-
ing on the self-resonant frequency of capacitors as it
exhibits the frequency response similar to a notch filter.
Depending on the manufacturer, 10pF to 20pF capaci-
tors typically exhibit self resonance at RF frequencies.
These capacitors, when placed at the input pins, can
effectively shunt the RF noise at the inputs of the
MAX9879. For these capacitors to be effective, they
must have a low-impedance, low-inductance path to
the ground plane. Do not use microvias to connect to
the ground plane as these vias do not conduct well at
RF frequencies.
______________________________________________________________________________________
8
m/s, and f = the RF frequency of
1
/
4
λ = c/f
the wavelength of the RF fre-
with DirectDrive Headphone Amplifier
RF Susceptibility
Stereo Class D Audio Subsystem
For the latest application details on UCSP construction,
dimensions, tape carrier information, PCB techniques,
bump-pad layout, and recommended reflow tempera-
ture profile, as well as the latest information on reliability
testing results, refer to the Application Note 1891:
Understanding the Basics of the Wafer-Level Chip-
Scale Package (WL-CSP) on Maxim’s website at
www.maxim-ic.com/ucsp. See Figure 15 for the rec-
ommended PCB footprint for the MAX9879.
Figure 15. PCB Footprint Recommendation Diagram
UCSP Applications Information
45±5μm
250μm
29