BU8241F Datasheet, PDF (9/11 Pages) Rohm – Cross point mixer for telephones

Communication ICs
BU8241F / BU8241FS / BU8242F / BU8244F
FOperation notes
(1) Turning on the power supply
When the power supply is turned on, the shift register is
in an indeterminate state. After turning on the power sup-
ply, switch settings should be entered by supplying shift
clock pulses to shift 64 bits of data into the shift register,
and then setting the LATCH pin to HIGH. (For the
BU8244, send 16 clock pulses.)
(2) Setting serial data
If the number of bits shifted or clock pulses applied is less
than or more than the number stated above, the switches
will not be set properly. Never apply shift clock pulses
when the LATCH pin is HIGH. Doing so will change the
data latch contents.
(3) Drive impedance
The input impedance Zin is 80 ± 32kΩ.
To suppress input gain and loss, we recommend using
the drive impedance shown in the table below.
If the level is to be attenuated at the input pin, make sure
the level is not affected by the internal resistance of the
IC, as shown in Figure 10. This can cause gain and / or
loss.
(4) Gain and noise when mixing signals
Increasing the number of signals mixed in a single output
(increasing the number of switches connected to the
same output amplifier that are on) causes a slight drop
in gain. With the BU8241 and BU8241FS /
BU8242F, increasing the number of signals mixed in a
single output (increasing the number of switches con-
nected to the same output amplifier that are on) causes
a slight increase in the noise level in terms of logic. If
noise is a problem, we recommend limiting the number
of signals mixed in a single output.
(5) Output load capacitance
The capacitance connected to GND in relation to an out-
put pin (the output load capacitance) should be kept to
50pF or lower. (BU8241F / BU8241FS / BU8242F)
FElectrical characteristic curves
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