ST3917A

ST3917B

SPEECH - TONE/PULSE DIALER - LED INDICATOR

July 1996

SPEECH CIRCUIT

.

2 TO 4 WIRES CONVERSION

.

PRESENT THE PROPER DC PATH FOR THE LINE

CURRENT AND THE FLEXIBILITY TO ADJUST IT

AND ALLOWPARALLEL PHONE OPERATION

.

SYMMETRICAL HIGH IMPEDANCE MICRO-

PHONE INPUTS SUITABLE FOR DYNAMIC,

ELECTRET OR PIEZOELECTRIC TRANSDUCER

.

ASYMMETRICAL EARPHONE OUTPUT SUIT-

ABLE FOR DYNAMIC TRANSDUCER

.

LINE LOSS COMPENSATION FIXED INTER-

NALLY BY A.G.C.

.

INTERNAL MUTING TO DISABLE SPEECH

DURING DIALING AND EXTERNAL MUTING

TO DISABLE TRANSMIT AMPLIFIER DURING

CONVERSATION MODE

.

LED INDICATOR EITHER FOR KEYBOARD ILLU-

MINATION (OR ON-LINE INDICATION) DURING

DIALING AND CONVERSATION OR FOR TONE

MODE INDICATION, THROUGH MU/MFI PIN

DIALER CIRCUIT

.

STORE UP TO 32 DIGITS FOR LAST NUMBER

REDIAL BUFFER, LNR IS INHIBITED IF THERE

ARE MORE THAN 32 DIGITS STORED

.

ALLOWMIXED MODE DIALING IN PULSE MODE

.

PACIFIER TONE PROVIDES AUDIBLE INDI-

CATION OF VALID KEY PRESSED IN A BUZZ-

ER OR/AND IN THE EARPHONE

.

TIMED PABX PAUSE / 10PPS PULSE RATE

.

MAKE/BREAK RATIO : 40/60 (ST3917A) AND

33/67 (ST3917B)

.

4 SELECTABLE OPTIONS ON FLASH DURA-

TION AND SOFTSWITCH INHIBITION IN ONE

OF THE OPTION WITH 100ms FLASH TIMING

.

2 SELECTABLE OPTIONS : TRANSMIT MUTE

TOGETHER WITH LED FOR KEYBOARD ILLUMI-

NATION OR LED FOR TONE MODE INDICATION

.

CONTINUOUS TONE FOR EACH DIGIT UNTIL

KEY RELEASE

.

USES INEXPENSIVE 3.579545MHz CERAMIC

RESONATOR

.

POWERED FROM TELEPHONE LINE, LOW

OPERATING VOLTAGE FOR LONG LOOP AP-

PLICATION

DESCRIPTION

The device consists of the speech and the dialer func-

tions. It provides the DC line interface circuit that termi-

nates the telephone line, analog amplifier for speech

transmission and necessary signals for either DTMF

and pulse dialing. When mated with a tone ringer, a

complete telephonecan be producedwith just two ICs.

TheDC lineinterfacecircuit developsits ownlinevoltage

acrossthedeviceandit is adjustableby external resistor

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

VDDandGND or anyrow respectively.The LEDcurrent

is limited to 17mA (typical).

The speech network provides the two to four wires inter-

face,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

sequence. Redial is then delayed until an outside line

can be accessed or some other activities occur before

normal signalling resumes. A LND key automatically

redials the last number dialed.

Adedicatedpin MU/MFI is used to select the muting for

transmit amplifier and lighted dial LED for keyboard

illumination or a LED indicator for tonemode indication.

The SEL pin allows selection of any one of the four

possible Flash duration options.

DIP28

(Plastic Package)

ORDER CODES :

ST3917AN - ST3917BN

SO28

(Plastic Package)

ORDER CODES :

ST3917AD - ST3917BD

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