BU8874 Datasheet, PDF (9/10 Pages) Rohm – DTMF receiver for telephones

Communication ICs
FOperation notes
(1) Power down
When ACK is LOW, the power down mode can be en-
tered by applying a rising edge to the PWDN pin. Current
consumption drops from several seconds to several tens
of seconds after the power down mode has been speci-
fied.
Operation with SD multiple reading is recommended.
BU8874 / BU8874F
(2) Oscillation
Oscillation frequency precision can be a problem with ce-
ramic resonators. Before including a ceramic resonator
in your design, please consult the resonator manufactur-
er to make sure this will not be a problem.
Also, if an external clock is being injected, a DC blocking
capacitor must be inserted. Select a capacitor that will
neither attenuate the frequency components or put an
excessive load on the drive side.
This LSI is not equipped with the power-on reset function. Also, since the internal circuit (flip-flop circuit) becomes unsta-
ble at the rising edge of the power supply, the internal circuit is initialized as shown below by the first DTMF sequence
received after the rising edge of the power supply. Therefore, input four dummy ACK pulses before the DTMF reception.
FElectrical characteristic curves
210