BU8871F データシートの表示（PDF） - ROHM Semiconductor

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BU8871F

DTMF receiver for telephones

ROHM Semiconductor 

Communication ICs

(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.

The relation between a momentary falter in the ESt guard

time (t.GL), 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.

BU8871F

FOperation notes

S 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.

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