Matsushita Electric KX-TSC35MXW, Service Manual

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Pin
NO.
Name
Description
13 XDI Input to the transmit detector system. The microphone amplifier output is ac coupled to
pin through an external resistor.
14 SKG High current ground pin for the speaker amp output stage. The SKG voltage should be
mV of the ground voltage at pin 22.
15 SKO Speaker amplifier output. The SKO pin will source and sink up to 100 mA when ac coupled
the speaker. The speaker amp gain is 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
used to prevent loading ac line signals. The required V+ voltage is 6.0 to 11 V (7.5 V nominal)
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 time of this circuit. The gain control loop limits the speaker
input to prevent clipping at SKO. The internal resistance at the AGC pin is nominally 110
18 CS Digital chip select input. When at a Logic "0" (<0.7 V) the Vcc regulator is enabled. When
Logic "1" (>1.6 V), the chip is in the standby mode drawing 0.5 mA. An open CS pin is a
"0". Input impedance is nominally 140 kohms. The input voltage should not 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.
can be used to power external circuitry such as a microprocessor (3.0 mA max). A filter
capacitor is required. The MC 34018 can be powered by a separate regulated supply by
connecting V+ and Vcc to a voltage between 4.5 V and 6.5 V while maintaining CS at a Logic
21 VB An output voltage equal to approximately Vcc/2 which serves as an analogue ground for
speakerphone system. Up to 1.5 mA of external load current may be sourced from VB.
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 words or phrases. When the XDC pin voltage decays to ground,
the attenuators switch from the transmit mode to the idle mode. The internal resistor at
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 pin voltage should be less than or equal to VB.
25 ACF Attenuator control filter. A capacitor connected to this pin reduces noise transients as
attenuator control switches levels of attenuation.
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
gain is directly proportional to the RRX resistance.
11. MODULE BLOCK DIAGRAM
11.1. LCD MODULE BLOCK
34