Panasonic KX-T2373MXW Service Manual

Panasonic KX-T2373MXW Service Manual Manual pdf 14 page image

7.2. Speakerphone IC DataPinNO.Name Description1 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 tothe 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 externalcircuit 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 resistorincreases 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 thetransmit 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 resistorincreases 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 thereceive 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 pin22.15 SKO Speaker amplifier output. The SKO pin will source and sink up to 100 mA when ac coupled to the speaker. The speaker amp gainis internally set at 34 dB (50 V/V).16 V+ Input dc supply voltage. V+ can be powered from Tip and Ring if an ac decoupling inductor is used to prevent loading ac linesignals. The required V+ voltage is 6.0 to 11 V (7.5 V nominal) at 7.0 mA.17 AGC A capacitor from this pin to VB stabilizes the speaker amp gain control loop, and additionally controls the attack and decay timeof this circuit. The gain control loop limits the speaker amp input to prevent clipping at SKO. The internal resistance at the AGCpin is nominally 110 kohms.18 CS Digital chip select input. When at a Logic "0" (<0.7 V) the Vcc regulator is enabled. When at a Logic "1" (>1.6 V), the chip is in thestandby mode drawing 0.5 mA. An open CS pin is a Logic "0". Input impedance is nominally 140 kohms. The input voltage shouldnot exceed 11 V.19 SKI Input to the speaker amplifier. Input impedance is nominally 20 kohms.20 Vcc A 5.4 V regulated output which powers all circuit expect the speaker amplifier output stage. Vcc can be used to power externalcircuitry such as a microprocessor (3.0 mA max). A filter capacitor is required. The MC 34018 can be powered by a separateregulated supply by connecting V+ and Vcc to a voltage between 4.5 V and 6.5 V while maintaining CS at a Logic "1".21 VB An output voltage equal to approximately Vcc/2 which serves as an analogue ground for the speakerphone system. Up to 1.5 mAof external load current may be sourced from VB. Output impedance is 250 ohms. A filter capacitor is required.22 Gnd Ground pin for the IC (except the speaker amplifier).23 XDC Transmit detector output. A resistor and capacitor at this pin hold the system in the transmit mode during pauses between wordsor phrases. When the XDC pin voltage decays to ground, the attenuators switch from the transmit mode to the idle mode. Theinternal resistor at XDC is nominally 2.6 kohms.24 VLC Volume control input. Connecting this pin to the slider of a variable resistor provides receive mode volume control. The VLC pinvoltage should be less than or equal to VB.25 ACF Attenuator control filter. A capacitor connected to this pin reduces noise transients as the attenuator control switches levels ofattenuation.26 RXO Output of the receive attenuator. Normally this pin is ac coupled to the input of the speaker amplifier.27 RXI Input of the receive attenuator. Input resistance is nominally 5.0 kohms.28 RRX A resistor to ground determines the nominal gain of the receive attenuator. The receive channel gain is directly proportional to theRRX resistance.14KX-T2373MXW