BH3866AS Datasheet, PDF (24/25 Pages) Rohm – Dual-line serial control sound processor IC

Video ICs
BH3866AS
(14) The necessity for Cch and the application
If there are only a left and right speaker, moving slightly
to the left or right of the television set causes a differ-
ence in the sound paths, and a characteristic trough
from 500Hz to 2kHz is created by the ensuing interfer-
ence, producing a muffled or contained sound. Also, lis-
teners positioned to the left or right hear the sounds from
the closest speaker causing the positions of the image
and sound to not match. Due to their setup, low-pitched
sounds are produced more easily from the left and right
speakers. However, in front of the speakers, because
the placement of the speakers directs the sound in a
cone-shaped direction, traveling along the sides of the
television, a "port" effect results and the sound becomes
muffled. To solve this problem, a center speaker is pro-
vided, and assuming this speaker is attached directly to
the center grille, the orientation and clarity are improved
significantly. Also, as a center channel application, this
can be used to adjust the microphone mixing level,
enabling use of the set as a karaoke set.
(15) Noise when the step is switched
In the application circuit example, using the SRV, SLV,
SCV, STB, and STT pins as an example, constants are
provided for each. These constants change depending
on the signal level setting, the mounting wiring pattern,
and other factors. Careful consideration should be given
to the constants before they are determined. An internal
equivalent circuit is shown below. (A primary integration
circuit is set, so that changes are implemented slowly.)
R Each pin
+
–
C
(External)
Fig.16
R value (kΩ)
SRV, SLV, SCV, STB, STT
30
(16) Level settings for volume and tone
In this databook, values are noted for the control serial
data in relation to the amount of attenuation or gain, as
reference values. Since the internal D / A converter is
configured on the R-2R system, data exists in locations
where there are no continuous changes between one
item of data and the next. This can be used where
detailed settings are required. However, the volume
must be set within eight bits (256 steps), and the tone
24
within seven bits (64 + 1 step).
(17) I²C BUS control
High-frequency digital signals are input to the SCL and
SDA pins, so the wiring and wiring patterns must be
arranged in such a way that they do not interfere with
the analog signal system line.
(18) Power On Reset
When the power supply is turned on, an internal circuit
carries out an initialization within the IC. When the power
supply is turned on, the volume levels of the left, right,
and center channels are set to – ∞, and the DAC output
(pin 17) is set to 0V. Once it has been turned on, if the
power supply is turned off and then immediately turned
on again, if there is any residual load on the capacitor,
there may be cases when the status described above
does not occur. If this happens, operation should be car-
ried out with the muting function on, until an I²C BUS
command is transmitted.
(19) Vref (pin 8) capacitor
A capacitance of 100µF is recommended for the power
supply filter attached to VREF. If this capacitance is set
too low, the minimum attenuation level of the volume
deteriorates. Crosstalk also tends to deteriorate. The IC
contains internal pre-charge and discharge circuits for
the capacitor attached to Vref.
(20) Excessive input
Steps have been taken with this product to avoid a situa-
tion in which, if a signal is input which exceeds the maxi-
mum input voltage for the LIN, RIN, and CIN pins, a
rebound waveform is produced even if hard clipping of
the output signal is implemented. Consequently, there is
no need to worry that the listener will hear distorted
sound because of a rebound waveform.
(21) Request concerning the fundamental design
Due to its pin layout, it is difficult to remove crosstalk
from the left channel to the center channel in this IC.
This is because the output signal at LOUT (pin 20) over-
laps the capacitance coupling of CB (pin 21) and CT (pin
22). This should be given adequate consideration in the
fundamental design of the set, when the pattern is laid
out. The following illustration shows an example of coun-
termeasures.
LOUT
CB
19
20
C+
10µ
Lch output
C
0.033µ
CT
21
C
470p