MC34118
     
                    VOICE SWITCHED SPEAKERPHONE CIRCUIT
     
     The MC34118  Voice  Switched  Speakerphone  Circuit  incorporates  the
nessesary amplifier, attenuators, level detectors, and control algorithm to
form the heart for a high quality hands-free speacerphone system . Included
are a microphone amplifier with adjustable gain and MUTE control.  Transmit
and Receive attenuators which operate  in  a  complementary  manner,  level
detectors  at  both  input  and output of both attenuators,  and background
noise monitors for both the transmit and  receive  channals.  A  Dial  Tone
Detector  prevents  the  dial  tone  fom  being  attenuated  by the Receive
baskgrounds noise  monitor  circuit.  Also  included  are  two  line  drive
ampifiers which can be used to form a hybrid network in conjunction with an
external coupling transforsmer.  A high-pass filter can be used  to  filter
out 60Hz noise in the receive channel,  or for other filtering functions. A
Chip Disable pin permits powering down the entire circuit to conserve power
on long loops where loop current is at a minimum.
     The MC34118 may be operated from a power supply,  or it can be powered
from  the  telephone  line,  requiring  typically  5mA.  The MC34118 can be
interfaced directly to Tip and Ring (thought a  coupling  transformer)  for
stand-alone  operation,  or  it  can  be  used in cojunction with a handset
speech network and/or other features of a featurephone.
     
                                 FEATURES
     - Improved Attenuator Gain Range: 52dB Between Transmit and Receive
     - Low Voltage Operation for Line-Powered Applications (3...6,5V)
     - 4-Point Signal Sencing for Improved Sencitivity
     - Background Noise Monitors for Both Transmit and Receive Parts
     - Microphone  Amplifier Gain Set by External Resistors - Mute Function
       Included
     - Chip Disable for Active/Standby Operation
     - On Board Filter Pinned-Out for User Defined Function
     - Dial  Tone  Detector  to  Inhibit Receive Idle Mode during Dial Tone
       Presence
     - Standart 28-Pin Plastic DIP Package and SOIC Package Avaible
     - Compatible with MC34119 Speaker Amplifier
     
                          ABSOLUTE MAXIMUM RATING
     Supply Voltage (Pin4)                            -1,+7V
     Voltage at CD (Pin3), MUT (Pin12)                -1,Vcc+1V
     Volage at VLC (Pin13)                            -1,Vcc+0,5V
     Voltage at TXI (Pin9), RXI (Pin21), FI (Pin2)    -0,5;Vcc+0,5V
     
     RECOMMENDED OPERATING LIMITS                   Min     Typ    Max
     Supply Limits (Pin4)                           3,5Vdc   -     6,5Vdc
     CD Input (Pin3), MUT (Pin12)                   0        -     Vcc
     Ivb Current (Pin15)                             -       -     500mkA
     VLC (Pin13)                                    0,3xVb   -     Vb,Vdc
     Attenuator Input Signal Voltage (Pin9,21)      0        -     350mVrms
     Microphone Amplifier, Hibrid Amplifier Gain    0        -     40dB
     Load Current @ RXO, TXO (Pin8,22)              0        -   -+2mA
                  @ MCO(Pin10)                      0        -   -+1mA
                  @ HTO-, HTO+ (Pin6,5)             0        -   -+5mA
     Ambient Temperature Range                     -20C      -    +60C