15.3 Speakerphone IC Data
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Pin
NO.
Name Description
1 RR A resistor to ground provides a reference current for the transmit and receive attenuators.
2 RTX A resistor to ground determines the nominal gain of the transmit attenuator. The transmit channel gain is inversely
proportional to the RTX resistance.
3 TXI Input to the transmit attenuator. Input resistance is nominally 5.0 kohms.
4 TXO Output to the transmit attenuator. The TXO output signal drives the input of the transmit level detector, as well as
the external circuit which drives the telephone line.
5 TLI Input of the transmit level detector. An external resistor ac coupled to the TLI pin sets the detection level.
Decreasing this resistor increases the sensitivity to transmit channel signals.
6 TLO Output of the transmit level detector. An external resistor and capacitor set the time the comparator will hold the
system in the transmit mode after speech ceases.
7 RLI Input of the receive level detector. An external resistor ac coupled to the RLI pin sets the detection level.
Decreasing this resistor increases the sensitivity to receive channel signals.
8 RLO Output of the receive level detector. An external resistor and capacitor set the time the comparator will hold the
system in the receive mode after the receive signal ceases.
9 MCI Microphone amplifier input. Input impedance is nominally 10 kohms and the dc bias voltage is approximately
equal to VB.
10 MCO Microphone amplifier output. The mic amp gain is internally set at 34 dB (50 V/V).
11 CP1 A parallel resistor and capacitor connected between this pin and Vcc holds a voltage corresponding to the
background noise level. The transmit detector compares the CP1 voltage with the speech signal from CP2.
12 CP2 A capacitor at this pin peak detects the speech signals for comparison with the background noise level held at CP1.
13 XDI Input to the transmit detector system. The microphone amplifier output is ac coupled to the XDI pin through an
external resistor.
14 SKG High current ground pin for the speaker amp output stage. The SKG voltage should be within 10 mV of the ground
voltage at pin 22.
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