Evaluates: MAX9737
MAX9737 Evaluation Kit
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Filtered Output
Audio analyzers typically cannot accept pulse-width
modulated (PWM) signals at their inputs. Therefore, the
MAX9737 EV kit features a lowpass filter at the output
to ease evaluation. Use the filtering output posts
(FOUT+, FOUT-) to connect the filtered PWM output to
the audio analyzer. The default lowpass filter at the EV
kit output is optimized for an 8Ω speaker.
Filterless Output
The MAX9737 EV kit’s filterless outputs (OUT+, OUT-)
can be connected directly to a speaker load without
any filtering. Use the OUT+ and OUT- test points to
connect the speaker directly to the MAX9737 output
using twisted-pair cable. Remove inductors L1 and L2
for maximum efficiency.
Output Filtering Requirements
To ease evaluation, the MAX9737 EV kit is shipped with
inductor-based output filters. However, the MAX9737
meets EN55022B EMC radiation limits with an inexpen-
sive ferrite bead and capacitor filter, especially when
speaker-wire lengths are less than 1m.
To install the ferrite-bead filters, first remove the large
filter inductors (L1, L2). Next, replace resistors R3 and
R4 with ferrite beads listed in Table 1, and install filter
capacitors on C10 and C11 pads. The speaker wires
should be connected to the OUT+ and OUT- test points
using twisted-pair cable.
Although component selection for the output filter is
dependent on speaker-wire length, the components in
Table 1 are provided with the EV kit as a starting point.
Final component selection should be determined dur-
ing EMC testing. Contact the factory if required.
Jumper Selection
Mute Function (MUTE)
The MAX9737 features a mute function to mute the
audio output of the EV kit. Place a shunt on JU1 for nor-
mal operation. Remove the shunt on JU1 to drive MUTE
low and place the part in mute mode. See Table 2 for
shunt positions.
Digital Inputs Power Supply (DVDD)
The MAX9737 EV kit operates from a DC power supply
between 8V and 28V. This power-supply range is too
high for the digital input pins on the MAX9737 IC. The
EV kit includes a circuit to regulate the input power
supply to 5V for powering all the logic circuits on the
EV kit. Jumper JU2 sets the DVDD voltage (see Table 3
for shunt positions).
Table 1. Recommended EMI Filter
Components for 8Ω Loads
