L3916A_1 datasheet(4/15 Pages) STMICROELECTRONICS

Part #	L3916A

Description	SPEECH AND 14 MEMORY DIALER WITH LED DRIVER

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

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IREF

Pin 13. An external resistor of 3.6kOhm con-

nected between IREF and GND will set the inter-

nal current level. Any change of this resistor value

will influence the microphone gain, DTMF gain,

earphone gain and sidetone.

VCC

Pin 14, VCC is the positive supply of the speech

network. It is stabilized by a decoupling capacitor

between VCC and GND. The VCC supply voltage

may also be used to supply external peripheral

circuits.

LED

Pin 15. Lighted dial indicator. The LED connected

to this pin will light up when the telephone is off-

hook and consuming 25% of the line current.

ILINE

Pin 16. A recommended external resistor of

20ohm is connected between ILINE and GND.

Changing this resistor value will have influence on

microphone gain, DTMF gain, sidetone, maximum

output swing on LN and on the DC characteristics

(especially in the low voltage region).

LN

Pin 17. LN is the positive line terminal of the de-

vice.

REG

Pin 18. The internal voltage regulator has to be

decoupled by a capacitor from REG to GND. The

DC characteristics can be changed with an exter-

nal resistor connected between LN and REG or

between REG and ILINE .

GTX, MIC–, MIC+

GTX (pin 19), MIC– (pin 20) and MIC+ (pin 21).

The one chip phone has symmetrical microphone

inputs. The amplification from microphone inputs to

LN is 51.5dB and it can be adjusted between 43.5

and 51.5dB. The amplification is proportional to ex-

ternal resistor connected between GTX and REG.

GDTMF

Pin 22. When the DTMF input is enabled, the mi-

crophone inputs and the receive amplifier input will

be muted and the dialing tone will be sent to the

line. The voltage amplification from GDTMF to LN

is 40dB. Final ouput level on LN can be adjusted

via the external resistor connected between

GDTMF and GND through a decoupling capaci-

tor. A confidence tone is sent to the earphone

during tone dialing. The attenuation of the confi-

dence tone from LN to Vear is –32dB typically.

VDD

Pin 23. VDD is the positive supply for the dialing

network and must meet the maximum and mini-

mum voltage requirements.

DEVICE OPERATION

During on-hook all keypad inputs are high imped-

ance internally and it requires very low current for

memory retention. At anytime, Row and Column

inputs assume opposite states at off-hook. The

circuit verifies that a valid key has been entered

by alternately scanning the Row and Column in-

puts. If the input is still valid following 32ms of de-

bounce, the digit is stored into memory, and dial-

ing

begins

after

a

pre-signal

delay

of

approximately 40ms (measured from the initial

key closure). Output tone duration is shown in Ta-

ble 1.

The device allows manual dialing of an indefinite

number of digits, but if more than 32 digits are di-

aled, it will ”wrap around”. That is, the extra digits

beyond 32 will be stored at the beginning of LND

buffer, and the first 32 digits will no longer be

available for redial.

Table 2: DTMF Output Frequency

Key Input

Stadard

Frequency

Actual

Frequency

% Deviation

ROW 1

ROW 2

ROW 3

ROW 4

697

770

852

941

699.1

766.2

847.4

948.0

+0.31

–0.49

–0.54

+0.74

COL 1

COL 2

COL 3

1209

1336

1477

1215.9

1331.7

1471.9

+0.57

–0.32

–0.35

NORMAL DIALING

D1

D2

D3

....etc

Normal dialing is straighforward, all keyboard en-

tries will be stored in the buffer and signaled in

succession.

PROGRAMMING AND REPERTORY DIALING

To program, enter the following:

PROG D1 D2 D3. . . Dn MEM (Location 0-9)

or

PROG

D1

D2. . . .Dn

E1-E3

During programming, dialing is inhibited.

FUNCTION PIN DESCRIPTION (continued)

L3916A - L3926A - L3936A

4/15

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