MAX9726 Maxim Integrated Products, MAX9726 Datasheet - Page 19

• Manufacturer Part Number: MAX9726
• Description: Headphone Amplifier
• Manufacturer: Maxim Integrated Products

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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
to roll off. f
boost gain no longer effects the transfer function. At
frequencies greater than or equal to f
by resistors R
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.
To configure the MAX9726 as an active single-pole low-
pass filter (Figure 9), connect a single feedback capac-
itor (C
-3dB point (below passband) of the active lowpass filter
is equal to:
Table 8. BassMax Pole and Zero
Examples for a Gain Boost of 8.8dB
(R1 = 47kΩ, R2 = 22kΩ)
POLE
Single-Pole Active Lowpass Filter (LPF)
C3 (nF)
F
is the frequency at which the gain boost begins
100
) in parallel with the feedback resistor (R
82
68
56
47
22
10
ZERO
f
f
POLE
ZERO
IN
and R
f
−
is the frequency at which the bass-
3
______________________________________________________________________________________
dB
=
=
BassMax, I
2
f
2
POLE
F
=
DirectDrive, Headphone Amplifier with
π
π
and the volume control attenua-
×
174
384
2π
×
38
47
56
68
81
C
R
R
C
R C
(Hz)
1
1
3
3
1
F F
−
+
×
×
R
R
R
R
2
2
1
1
(
×
Hz
×
R
R
)
2
2
ZERO
(
(
Hz
Hz
f
)
)
ZERO
, the gain set
1060
106
130
156
190
230
490
(Hz)
2
F
C, Volume and Gain Control
). The
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
dielectric capacitors are good choices for feedback
capacitors. Capacitors with high-voltage coefficients,
such as ceramics (non-C0G dielectrics), can result in
increased distortion.
Figure 8. BassMax Gain Profile Example
Figure 9. Single-Pole Active Lowpass Filter
R
IN
-10
10
-2
-4
-6
-8
8
6
4
2
0
10
f
POLE
BassMax DISABLED
BassMax FREQUENCY RESPONSE
IN_
BassMax ENABLED
100
FREQUENCY (Hz)
MAX9726
R
f
C
-3dB
F
f
F
ZERO
=
2πR
1
F
C
1k
F
FB_
R1 = 47kΩ
R2 = 22kΩ
C3 = 0.1µF
R
L
= 32Ω
F
. Film or C0G
10k
TO
ATTENUATOR
STAGE
19