Datasheet

POLE
1
CA
2 f (RA RB)
=
π ×−
Figure 13 shows the frequency response of the circuit in
Figure 12. With RA = 47kΩ, RB = 22kΩ, and CA = 0.33μF,
the passband gain is set to 8.8dB.
Layout and Grounding
Proper layout and grounding are essential for optimum
performance. Connect PGND and SGND together at a
single point on the PC board. Connect PV
SS
to SV
SS
and bypass with a 1μF capacitor to PGND. Bypass V
DD
to PGND with a 1μF capacitor. Place the power-supply
bypass capacitor and the charge-pump capacitors as
close to the MAX9723 as possible. Route PGND and all
traces that carry switching transients away from SGND
and the audio signal path. Route digital signal traces
away from the audio signal path. Make traces perpen-
dicular to each other when routing digital signals over or
under audio signals.
The thin QFN package features an exposed paddle that
improves thermal efficiency. Ensure that the exposed
paddle is electrically isolated from PGND, SGND, and
V
DD
. Connect the exposed paddle to SV
SS
when the
board layout dictates that the exposed paddle cannot
be left floating.
Figure 12. Using BassMax to Increase MAX9723’s Maximum
Gain
Figure 13. Increasing the Maximum Gain Using BassMax
Table 12. BassMax Gain Examples
(R1 = 47kΩ)
Table 13. BassMax Pole and Zero
Examples for a Gain Boost of 8.8dB
(R1 = 47kΩ, R2 = 22kΩ)
C3 (nF) f
POLE
(Hz) f
ZERO
(Hz)
100 38 106
82 47 130
68 56 156
56 68 190
47 81 230
22 174 490
10 384 1060
R2 (kΩ) AV GAIN (dB)
39 20.6
33 15.1
27 11.3
22 8.8
15 5.7
10 3.7
CA
RB
RA
R
R
OUT_
BB_
AUDIO
INPUT
BassMax
ENABLE
MAX9723
FREQUENCY RESPONSE OF FIGURE 12
FREQUENCY (Hz)
A
V
(dB)
1k100101
1
2
3
4
5
6
7
8
9
10
0
0.1 10k
MAX9723A
CMD REGISTER
CODE = 0xFF
RA = 47kΩ
RB = 22kΩ
CA = 0.33mF
MAX9723 Stereo DirectDrive Headphone Amplier
with BassMax, Volume Control, and I
2
C
www.maximintegrated.com
Maxim Integrated │ 19