BU8872FS-E2 Datasheet, PDF (8/10 Pages) Rohm – DTMF receiver for telephones BU8872 / BU8872FS

Communication ICs
(3) DTMF input
BU8872 / BU8872FS
The relation between a momentary falter in the ESt guard
time (tGL), a momentary HIGH level in the ESt guard time
(tGH), and the time constant is shown below. Figure 10
shows a timing diagram for guard times.
C501 : This is the DC blocking capacitor. Select a ca-
pacitor that will pass DTMF signals (greater
than 697Hz) without significantly attenuating
the signals.
JP592 : If DTMF signals are being input directly, both
ends should be shorted.
C591
R591 X R595 ^{Use these to increase the sensitivity of}
C592, C593 ^{the DTMF receiver.}
(4) ESt output
The ESt guard time is determined by the CPU of the host
computer, but to reduce the load on the host computer,
the guard time can be set using an external circuit, as
shown below.
199