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1734709-9

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P18P19-P21P22-P24
The low-frequency boost attained by the BassMax cir-
cuit is added to the gain realized by the maximum gain
and volume settings. Select the BassMax gain so that
the output signal remains within the dynamic range of
the MAX9726. Output signal clipping occurs at low fre-
quencies if the BassMax gain boost is excessively
large. See the
Output Dynamic Range
section.
Capacitor C3 forms a pole and a zero according to the
following equations:
f
POLE
is the frequency at which the gain boost begins
to roll off. f
ZERO
is the frequency at which the bass-
boost gain no longer effects the transfer function. At
frequencies greater than or equal to f
ZERO
, the gain set
by resistors R
IN
and R
F
and the volume control attenua-
tion dominate. Table 8 contains a list of capacitor val-
ues and the corresponding poles and zeros for a given
DC gain. See Figure 8 for an example of a gain profile
using BassMax.
Single-Pole Active Lowpass Filter (LPF)
To configure the MAX9726 as an active single-pole low-
pass filter (Figure 9), connect a single feedback capac-
itor (C
F
) in parallel with the feedback resistor (R
F
). The
-3dB point (below passband) of the active lowpass filter
is equal to:
The passband gain of the active filter is determined by
the external component values described in the
Gain-
Setting Components
section.
To minimize distortion, use capacitors with low-voltage
coefficient dielectrics when selecting C
F
. Film or C0G
dielectric capacitors are good choices for feedback
capacitors. Capacitors with high-voltage coefficients,
such as ceramics (non-C0G dielectrics), can result in
increased distortion.
f
RC
Hz
dB
FF
−
=
3
1
2π
()
f
RR
CRR
Hz
f
RR
CRR
Hz
POLE
ZERO
=
×××
=
+
×××
−12
2312
12
2312
π
π
()
()
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I
2
C, Volume and Gain Control
______________________________________________________________________________________
19
Table 8. 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
MAX9726 fig08
FREQUENCY (Hz)
GAIN (dB)
1k100
-8
-6
-4
-2
0
2
4
6
8
10
-10
10 10k
BassMax FREQUENCY RESPONSE
BassMax ENABLED
f
ZERO
f
POLE
R1 = 47kΩ
R2 = 22kΩ
C3 = 0.1μF
R
L
= 32Ω
BassMax DISABLED
Figure 8. BassMax Gain Profile Example
C
F
R
F
R
IN
FB_
IN_
TO
ATTENUATOR
STAGE
f
-3dB
=
1
2πR
F
C
F
MAX9726
Figure 9. Single-Pole Active Lowpass Filter
MAX9726
Summing Amplifier (Audio Mixer)
Figure 10 shows the MAX9726 configured as a sum-
ming amplifier, which allows multiple audio sources to
be linearly mixed together. Using this configuration, the
output of the MAX9726 is equal to the weighted sum of
the input signals:
As shown in the above equation, the weighting or
amount of gain applied to each input signal source is
determined by the ratio of R
F
and the respective input
resistor (R
IN1
, R
IN2
, R
IN3
) connected to each signal
source. When BassMax is enabled, the low-frequency
gain (A
BOOST
) set by R1, R2, and C3 (see the
Gain-
Setting Components
section) adds to the gain deter-
mined by R
F
and R
IN_
. Select R
F
and R
IN_
such that the
dynamic range of the MAX9726 is not exceeded when
BassMax is enabled and/or when the input signals are
at their maximum values and in phase with each other.
Layout and Grounding
Proper layout and grounding are essential for optimum
performance. Connect PGND and SGND together at a
single point (star ground point) on the PC board.
Connect PV
SS
to SV
SS
at the device and bypass this
connection with a 1µF capacitor to PGND. Bypass V
DD
,
PREG, and NREG to PGND with a 1µF capacitor. Place
the power-supply bypass capacitor and the charge-
pump hold capacitor as close as possible to the
MAX9726. 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 perpendicular to each
other when routing digital signals over or under audio
signals.
The TQFN package features an exposed pad that
improves thermal efficiency. Ensure that the exposed
pad is electrically isolated from PGND, SGND, and
V
DD
. Connect the exposed pad to PV
SS
when the
board layout dictates that the exposed pad cannot
be left unconnected.
UCSP Applications Information
For the latest application details on UCSP construction,
dimensions, tape carrier information, PC board tech-
niques, bump-pad layout, and recommended reflow
temperature profile, as well as the latest information on
reliability testing results, go to Maxim’s website at
www.maxim-ic.com/ucsp and look up the Application
Note:
UCSP—A Wafer-Level Chip-Scale Package
.
VV
R
R
V
R
R
V
R
R
OUT IN
F
IN
IN
F
IN
IN
F
IN
_
=++
⎛
⎝
⎜
⎞
⎠
⎟
−
1
1
2
2
3
3
DirectDrive, Headphone Amplifier with
BassMax, I
2
C, Volume and Gain Control
20
______________________________________________________________________________________
DIAGRAM SHOWN WITH BassMax DISABLED.
R
F
R
IN2
FB_
IN_
TO
ATTENUATOR
STAGE
V
FB_
=
+V
IN1
R
F
-( )
R
IN1
MAX9726
+ V
IN2
R
F
R
IN2
V
IN3
R
F
R
IN3
C
IN
V
IN2
R
IN1
C
IN
V
IN1
R
IN3
C
IN
V
IN3
Figure 10. Summing Amplifier
MAX9726
DirectDrive, Headphone Amplifier with
BassMax, I
2
C, Volume and Gain Control
______________________________________________________________________________________
21
Functional Diagram/Typical Operating Circuit
POSITIVE
REGULATOR
PREG
V
CC
V
DD
INL FBL
OUTL
BML
BMR
OUTR
V
EE
1μF
R
IN
10kΩ
10
(E2)
1
(A1)
20
(B2)
6
(C2)
7
(C3)
14
(B4)
2
(B1)
4
(D1)
13
(E4)
3
(C1)
5
(E1)
C
PREG
1μF
C
IN
1μF
C
IN
1μF
C
NREG
1μF
C1
1μF
9
(D2)
8
(B3)
18
(A2)
19
(C4)
15
(D4)
17
(A3)
R
F
10kΩ
LEFT AUDIO
INPUT
RIGHT AUDIO
INPUT
2.7V TO 5.5V
R1
47kΩ
R2
22kΩ
C3
0.1μF
C3
0.1μF
R2
22kΩ
R1
47kΩ
10kΩ
TO I
2
C
MASTER
R
F
AND R
IN
ARE CHOSEN FOR A GAIN OF 20dB.
BassMax CIRCUIT TUNED FOR +8.8dB AT 106Hz.
( ) UCSP PACKAGE
10kΩ
SDA
NEGATIVE
REGULATOR
NREG
SGND
PV
SS
16
(A4)
11
(E3)
SV
SS
INR
12
(D3)
FBR
I
2
C
INTERFACE
SCL
CHARGE
PUMP
C1P
C1N
V
CC
V
EE
R
R
0 TO 120dB
ATTENUATOR
V
CC
V
EE
V
CC
V
EE
0 TO 120dB
ATTENUATOR
R
R
SHDN
OFF
ON
C2
1μF
PGND
R
IN
10kΩ
V
EE
V
CC
R
F
10kΩ
MAX9726
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1734709-9

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TE Connectivity
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Headers & Wire Housings 9 POS HDR R/A 1.0mm
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