MULTIFREQUENCY INPUT 1
REGULATOR AC BYPASS 2
~ SIGNAL LEVEL
~6 + VLAND MF OUTPUT
5~ ACIDC CHARACT.ADJUSt
5- 40731 2
The L5342 interface the M751 and M761/761A tone diallers with the telephone line. Power is only
applied to the system when the handset is lifted and a key pressed. At this time 51 is also switched (see
fig. 2) disconnecting the speech circuit from the line and connecting the dialling circuit.
In the dialling condition the L5342 performs 3 functions:
1) D.C. and A.C. line termination
2) Tone dialler power supply
3) Amplification and transmission of tone pairs.
In the initial stage of switch-on the supply voltage VDD is regulated at ~ 4 volt. This overdrives the
M751/761/761A internal oscillator causing a rapid start-up and therefore rapid generation of output
When the system reaches its normal operating point the supply voltage VDD is stabilized at 2.5V ± 4%.
Rthi-amb Thermal resistance junction-ambient
max 100 °C/W