Datasheet
OBSOLETE
LM4550
SNAS032F –SEPTEMBER 2001–REVISED APRIL 2013
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Table 3. POWER SUPPLIES AND REFERENCES (continued)
Name Pin I / O Functional Description
Nominal 2.2 V internal reference
V
REF
27 O Not intended to sink or source current. Use short traces to bypass (3.3 µF, 0.1 µF) this pin to
maximize codec performance. This pin must be tied to AV
DD
with a 10 kΩ pull-up resistor.
Nominal 2.2 V reference output
V
REF_OUT
28 O
Can source up to 5 mA of current and can be used to bias a microphone.
Table 4. 3D SOUND AND NO-CONNECTS (NC)
Name Pin I / O Functional Description
These pins are used to complete the National 3D Sound stereo enhancement circuit. Connect a 0.022
µF capacitor between pins 3DP and 3DN. National 3D Sound can be turned on and off via the 3D bit
3DP, 3DN 33,34 O (bit D13) in the General Purpose register, 20h. National 3D Sound uses a fixed-depth type stereo
enhancement circuit hence the 3D Control register, 22h is read-only and is not programmable. If
National 3D Sound is not needed, these pins should be left open (NC).
29, 30
These pins are not used and should be left open (NC).
31, 32
NC NC For second source applications these pins may be connected to a noise-free supply or ground (e.g.
38, 42
AV
DD
or AV
SS
), either directly or through a capacitor.
43, 44
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