sames

SA545

16/18

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 150K

Ω 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.