L3281AB Fast Delivery |IC PHOENIX CO.,LIMITED

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L3281AB
LOW VOLTAGE TELEPHONE SPEECH CIRCUITS
L3281
LOW VOLTAGE TELEPHONE SPEECH CIRCUITS
PRELIMINARY DATA
OPERATION DOWN TO 1.6V/ 6.5mA
DTMF& BEEP TONE INPUTS
EXTERNAL MUTING FOR EARPHONE AND
MICROPHONE
SUITABLE FOR DYNAMIC EARPHONE AND
DYNAMIC OR ELECTRET MICROPHONE
AGC CONTROL ON BOTH SENDING AND
RECEIVING
DESCRIPTION
The L3281is an electronic speech circuit devel-
opedto replace hybrid circuitsin telephone sets
that can be operated in parallel with other
phones.
June 1993
BLOCK DIAGRAM
DIP14
ORDERING NUMBERS:
L3281AB L3281AD1
SO14
1/10
PIN CONNECTION (top view)
THERMAL DATA
Symbol Parameter Value Unit
DIP-14 SO-14
Rth j-amb Thermal Resistance Junction Ambient Max 90 130 °C/W
ABSOLUTE MAXIMUM RATINGS
Symbol Parameter Value Unit
DIP-14 SO-14 Line Voltage(3ms pulse) 15 V Line Current 150 mA
Ptot Total Power Dissipation, Tamb =55°C 1.0 0.6 W
Top Operating Temperature –20to55 °C Junction Temperature –65to 150 °C
L3281
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TEST CIRCUITS
Figure1.
Figure2. Figure3.
L3281
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ELECTRICAL CHARACTERISTICSIL=20to 100mA; R4 =(51Ω// diode)+ 33Ω; 25°C;f =1kHz; Unless Otherwise Specified
Symbol Parameter Test Condition Min. Typ. Max. Unit Line Voltage IL= 6.5mA= 20mA= 50mA= 80mA
CMRR Common Mode Rej. Ratio 50 dB
Gtx Sending Gain Vmi= 10mV;IL= 20mA 30 31.5 33 dB
DGtx Delta Sending Gain Vmi= 10mV;IL= 70mA – 7.2 –5.7 –4.2 dB
THDtx Sending Distortion Vso= 700mV;IL= 20mA 5 %
Ntx Sending Noise Vmi= 0V;IL= 50mA –70 dB
Zml Mic. Input Impedance Vmi= 10mV 40 kΩ
Grx Receiving Gain IL= 20mA;Vri= 0.2V – 10.7 – 9.2 – 7.7 dB
DGrx Delta Receiving Gain IL= 70mA;Vri= 0.2V – 7.2 – 5.7 – 4.2 dB
THDrx Receiving Distortion Vro= 350mV; Load= 350Ω
Vro= 300mV;IL =10 mA
Nrx Receiving Noise Vri=0V 100 μV
Zro Rec. Output Impedance Load= 200Ω;Vro= 50V 10 Ω
Sidetone Vmi= 10mV 10 20 dB Line Match. Impedance Vri= 0.2V 500 600 700 Ω
Vso Sending Output Voltage IL= 6.5mA; THD=5% 100 mV
Iro Receiving Output Current IL= 6.5mA; THD=5% 0.5 mAp
MUlo Mute Input Low Dialing Mode 50 100 μA
MUhl Mute Input Open Speaking Mode 1 μA
Gmf DTMF Gain VmfIN= 10mV 14.5 16 17.5 dB
Rmf DTMF Input Impedance 5 10 kΩ
THDmf DTMF Distortion VmfLN= 140mV 5 %
Gbeep Beeptone Gain VbeepIN= 25mV 8.5 dB
Rbeep Beeptone Input Impedance 5.5 8 kΩ
THDbeep Beeptone Distortion VbeepIN= 100mV;IL= 20mA 0.5 5 % Zener Voltage (Pin5) Iz=1 mA 4.2 5.1 6.2 V
Ileak Leakage Current,Vpin5 =3V 20 μA
L3281
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CIRCUIT DESCRIPTION
TWO TO FOUR WIRE CONVERSION
The L3281ABis based ona Wheastone bridge
configuration.To balance the bridge the following
relation mustbe satisfied:// Zm = R2
The AC signal from the microphoneis sentto one
diagonalof the bridge (pins1 and3).A small per-
centageof the signal poweris lost on Zb (being> (Zm//Zi)); the main partis sentto the line via
R2. receiving mode, the AC signal coming from the
LINEis sensed across the second diagonalof the
bridge (pins12 and2).
The impedance Zm andZb canbe complex.
LOGIC OF MUTE SWITCHING
MUTE DTMF BEEP MIC IMP RX IMP
LOW ACTIVETO LINE ACTIVETO EARPHONE MUTED MUTED
(DIAL) OUTPUT OUTPUT
OPEN ACTIVETO LINE ACTIVETO EARPHONE ACTIVE ACTIVE
(SPEECH) OUTPUT OUTPUT
Figure4: 2/4 WireConversion
L3281
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CHARACTERISTICThe fig.5 shows the equivalent simplified circuitof
the DC regulator that providesto give the oppor-
tune DC impedance Zdc.=
Idc⋅ Z4 ⋅ (RA+ RB)+ VD+ VR1=
(Idc⋅ Z4)⋅+1 VD+ VR1
since RA= RB= (Idc⋅ Z4⋅2)+ VD+ VR1
WhenIL 18 mA and considering neglectible the+ VR1 variation versus line current:
ZDC=Δ VL Idc=2 ⋅Z4IL= 6.5 mA no current flows through Z4 but
onlyin the restof the circuit for internal biasing
(Io;Ia). The bias currentIois fixedby the resistor
R2. The line voltagein this caseis:=Ia RA+ VR1= 1.6V
The Fig.6 shows the DC characteristic (voltage
between pin12 and pin3 versus line current).
The device own an equivalent zener voltageat
pin5 that canbe usedas supply voltage for elec-
tret microphone (see Block Diagram).
The valueof the resistor R2 and the capacitor C2
should be chosenin orderto not affect the AC
line inpedance. The Fig.7 shows the zener
equivalent.
The zener voltage will be:=
70K
13.6K+1⋅ Vbeis possibleto supply 1mAto the electrete volt-
ageif VL> (1mA+ Iz)⋅ Rz+Vz
Figure5: Equivalent Simplified Circuit
Figure6: Low Voltage Speech Circuit.
Figure7: Zener Equivalent.
L3281
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Partno	Mfg	Dc	Qty	Available	Descript
L3281AB	STM	N/a	1337	avai	LOW VOLTAGE TELEPHONE SPEECH CIRCUITS