Table of Contents
Advertisement
Pin
Name
NO.
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
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
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
pin through an external resistor.
14
SKG High current ground pin for the speaker amp output stage. The SKG voltage should be within
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
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 Logic
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
is required. The MC 34018 can be powered by a separate regulated supply by connecting
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
speakerphone system. Up to 1.5 mA of external load current may be sourced from VB. Output
impedance is 250 ohms. A filter capacitor is required.
Description
16
Advertisement
Table of Contents
