LM4946SQEVAL National Semiconductor, LM4946SQEVAL Datasheet - Page 25

• Manufacturer Part Number: LM4946SQEVAL
• Description: BOARD EVALUATION LM4946SQ
• Manufacturer: National Semiconductor
• Series: Boomer®r

Specifications of LM4946SQEVAL

• Amplifier Type: Class D
• Output Type: 1-Channel (Mono) with Stereo Headphones
• Max Output Power X Channels @ Load: 1.3W x 1 @ 8 Ohm; 85mW x 2 @ 32 Ohm
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Board Type: Fully Populated
• Utilized Ic / Part: LM4946
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

NATIONAL 3D ENHANCEMENT
The LM4946 features a stereo headphone, 3D audio en-
hancement effect that widens the perceived soundstage from
a stereo audio signal. The 3D audio enhancement creates a
perceived spatial effect optimized for stereo headphone lis-
tening. The LM4946 can be programmed for a “narrow” or
“wide” soundstage perception. The narrow soundstage has a
more focused approaching sound direction, while the wide
soundstage has a spatial, theater-like effect. Within each of
these two modes, four discrete levels of 3D effect that can be
programmed: low, medium, high, and maximum (Table 2, 3),
each level with an ever increasing aural effect, respectively.
The difference between each level is 3dB.
The external capacitors, shown in Figure 6, are required to
enable the 3D effect. The value of the capacitors set the cutoff
frequency of the 3D effect, as shown by Equations 1 and 2.
Note that the internal 20kΩ resistor is nominal.
(optional)
R
3D
10
20
FIGURE 6. External 3D Effect Capacitors
0
1
5
(kΩ)
f
f
3DR(-3dB)
3DL(-3dB)
= 1 / 2π * 20kΩ * C
= 1 / 2π * 20kΩ * C
C
3D
68
68
68
68
68
(nF)
3DL
3DR
0.05
0.25
0.50
1.00
M
0
TABLE 6. Pole Locations
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(1)
(2)
ΔAV (dB)
–0.4
–1.9
–3.5
–6.0
25
0
Optional resistors R
7) to affect the -3dB frequency and 3D magnitude.
ΔAV (change in AC gain) = 1 / 1 + M, where M represents
some ratio of the nominal internal resistor, 20kΩ (see exam-
ple below).
FIGURE 7. External RC Network with Optional R
f
f
3DL(-3dB)
3DR(-3dB)
f
3dB
f-3dB (3D)
(3D) = 1 / 2π (1 + M)(20kΩ * C
C
(Hz)
117
111
94
78
59
Equivalent
= 1 / 2π * (20kΩ + R
= 1 / 2π * 20kΩ + R
3DL
R
(new) = C
and R
3DR
to keep same
pole location
Value of C
Resistors
3DR
64.8
54.4
45.3
34.0
(nF)
3D
can also be added (Figure
/ 1 + M
3DR
3DL
3D
) * C
) * C
3D
3DR
3DL
)
new Pole
Location
www.national.com
(Hz)
117
117
117
117
3DL
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and
(3)
(4)
(5)
(6)