SA545 Datasheet, PDF (16/18 Pages) Sames – PULSE/DTMF SWITCHABLE DIALLERS WITH 10 REPERTORY MEMORIES

SA545
F. PIN 12 (SA545)/PIN 14 (SA54L5)
a) MUTE
b) MUTE
G. LNR Protocol
a) Numbers entered after * or # are never retained in the LNR store. (Attractive
for banking applications since PIN is not retained).
b) Numbers entered after * or # are retained in the LNR store if initial mode is
set to DTMF.
TYPICAL APPLICATIONS
The circuit in Figure 7 uses a constant current supply to draw current from the
telephone line which is used to power the SA54X5. The 2,5V reference diode
produces a stabilised supply voltage which determines the DTMF tone level of the
SA545.
In Figure 8, a stabilising voltage from the speech circuit is used to supply the SA545
during DTMF dialling to give accurate tone levels.
The SA545 is powered via the 150KΩ resistor during TBR operations and LD dialling
breaks, and via T1 during dialling makes. This configuration minimises the
component count, at the expense of allowing a leakage current of about 450µA
during dialling breaks. The 47µF reservoir capacitor maintains and smoothes the
supply to the chip.
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