ST3938B Datasheet | STMicroelectronics

DESCRIPTION The device consists of the speech and the dialer functions. It provides the DC line interface circuit that terminates the telephone line, analog amplifier for speech transmission and necessary signals for either DTMF and pulse dialing. When mated with a tone ringer, a plete telephonecan be producedwith just two ICs. The DClineinterfacecircuit developsits ownlinevoltage acrossthedeviceandit is adjustableby externalresistor to suit different country’s specification. A built-in LED driver can deliver excess line current to external LED indicator(s) during dialing and speech mode. The LED(s) can be used either for keyboard illumination purpose or for tone mode indication during softswitch and mixed mode dialing by connecting MU/MFI pin to VDDand GND oranyrowrespectively.The LEDcurrent is limited to 17m A (typical). The speech network provides the two to four wires interface,electronic switchingbetweendialingandspeechand automaticgain control on transmit and receive. The dialing network buffers up to 32 digits into the LND memorythatcan be laterredialedwith asinglekeyinput. Users can store all 13 signalling keys and access several unique functions with single key entries. These functions include : Pause, Last Number Dialled (LND), Softswitch and Flash. (see Figure 1). The FLASH key simulates a hookflash to transfercalls or to activate other special features provided by the PABX or central office. The PAUSE key stores a timed pause in the number...