MAX9761EVKIT Maxim Integrated, MAX9761EVKIT Datasheet - Page 21

• Manufacturer Part Number: MAX9761EVKIT
• Description: Amplifier IC Development Tools
• Manufacturer: Maxim Integrated
• Series: MAX9760, MAX9761, MAX9762, MAX9763r

depending on the status of the gain control input. The
stereo MAX9760/MAX9761 feature two gain options per
channel. The mono MAX9762/MAX9763 feature two
gain options per single-ended channel, and a single
gain option for the mono speaker amplifier (see Tables
1a and 1b for the gain-setting options).
The MAX9762 defaults to GAINM in speaker mode and
can switch between GAINA and GAINB in headphone
mode.
Headphones typically have a poor low-frequency
response due to speaker and enclosure size limitations.
A bass boost circuit compensates the poor low-frequen-
cy response (Figure 9). At low frequencies, the capaci-
tor C
the feedback loop (R
At the frequency:
where the impedance, C
high frequencies, the C
impedance of the feedback loop is:
Figure 9. Bass Boost Circuit
F
is an open circuit, and the effective impedance in
R
R
IN
F EFF
(
______________________________________________________________________________________
Stereo 3W Audio Power Amplifiers with
F(EFF)
V
2
BIAS
)
πR C
=
F,
C
1
F
F
R
R
F
) is R
2
F
F
is a short circuit. Here the
1
1
begins to decrease, and at
F
R
×
+
F1
R
F(EFF)
F2
R
R
F
F
2
2
Bass Boost Circuit
= R
Headphone Drive and Input Mux
F1
.
Assuming R
twice that of R
Thus, the amplifier has more gain at lower frequencies,
boosting the system’s bass response. Set the gain roll-
off frequency based upon the response of the speaker
and enclosure.
Good PC board layout is essential for optimizing perfor-
mance. Use large traces for the power-supply inputs
and amplifier outputs to minimize losses due to para-
sitic trace resistance, as well as route heat away from
the device. Good grounding improves audio perfor-
mance, minimizes crosstalk between channels, and
prevents any digital switching noise from coupling into
the audio signal. If digital signal lines must cross over
or under audio signal lines, ensure that they cross per-
pendicular to each other.
The MAX9760–MAX9763 QFN and TSSOP-EP pack-
ages feature exposed thermal pads on their under-
sides. This pad lowers the package’s thermal
resistance by providing a direct heat conduction path
from the die to the printed circuit board. Connect the
pad to signal ground by using a large pad, or multiple
vias to the ground plane.
Figure 10. Bass Boost Response
R
F1
R
R
R
IN
F1
IN
R
F2
F1
GAIN
= R
F(EFF)
F2
, then R
at high frequencies (Figure 10).
2π R
Layout and Grounding
1
F2
F(EFF)
C
F
at low frequencies is
FREQUENCY
21