To suppress this noise, and to provide a 2V
RMS
stan-
dard audio output level from a single 5V supply, the
MAX9724C can be configured as a line driver and
active lowpass filter. Figure 5 shows the MAX9724C
connected as 2-pole Rauch/multiple feedback filter with
a passband gain of 6dB and a -3dB (below passband)
cutoff frequency of approximately 27kHz (see Figure 6
for the Gain vs. Frequency plot).
Layout and Grounding
Proper layout and grounding are essential for optimum
performance. Connect PGND and SGND together at a
single point on the PCB. Connect PVSS to SVSS and
bypass with a 1µF capacitor. Place the power-supply
bypass capacitor and the charge-pump hold capacitor
as close to the MAX9724 as possible. Route PGND and
all traces that carry switching transients away from
SGND and the audio signal path. The thin QFN pack-
age features an exposed pad that improves thermal
efficiency. Ensure that the exposed pad is electrical-
ly isolated from PGND, SGND, and V
DD
. Connect the
exposed paddle to SVSS only when the board lay-
out dictates that the exposed pad cannot be left
floating.
UCSP Applications Information
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
UCSP—A
Wafer-Level Chip-Scale Package
available on Maxim’s
website at www.maxim-ic.com/ucsp.
MAX9724C/MAX9724D
Low RF Susceptibility DirectDrive Stereo Head-
phone Amplifier with 1.8V Compatible Shutdown
14 ______________________________________________________________________________________
vs. FREQUENCY
