2.1.5.2. Analog Low-pass
The output of the DAC is filterted by an analog low-
pass filter with a cut-off frequency of approximately
1.4 MHz. This filter removes the high-frequency com-
ponents of the noise-shaping signal.
Table 2–1:
AUXEN pin
AUXEN
0
1
2.1.5.3. Postfilter Op Amps
This block contains the active components for the
optional analog postfilters. It is recommended to use a
second-order filter (see Section 4. “Applications” on
caused by the noise shaper The op amps and all I/O-
pins for this block are shown in Fig. 2–2.
PRELIMINARY DATA SHEET
AUX not selected
AUX selected
This allows to use a jack that switches the AUXEN to
low when an analog source is plugged in, according to
the application note Section 4. “Applications” on page
mixer because the DAC is extremely quiet if no USB
audio is applied.
The AUXEN pin also keeps the UAC 3552A from
entering the low-power mode when an analog source
is connected. Please note that in this mode, the
UAC 3552A is not USB-compliant. If the USB is not
connected the GPIO pins work as an USB-indepen-
dent volume control (see Table 2–2). BassBoost is not
supported in this mode.
2.1.5.4. Input Mixer
This block is used to mix the auxiliary inputs and the
signals coming from the DAC. This allows to use an
UAC 3552A-based USB speaker in a non-USB envi-
ronment, like WIN 3.11 or other operating systems. On
the other hand, it allows to connect additional analog
sources, like CD-player or Walkman even while the
speaker is connected to the USB. The input mixer is
hardware-controlled by the AUXEN pin.
For external components
,
see section “Applications”
FOUTL
FOPL
FINL
UAC 3552A (Back-end)
Analog Vol. L
OUTL
−
from switch matrix
−
OUTR
−
−
Analog Vol. R
AVSS
VREF
AGNDC
FOUTR
FOPR
FINR
For external components
,
see section “Applications”
Fig. 2–2:
Postfilter op amps and analog volume
8
Micronas
MICRONAS [ MICRONAS ]
