4
U4090B-N
4740A–CORD–09/03
Pin Description
Pin
Symbol
Function
1
GT
A resistor from this pin to GND sets the amplification of the microphone and DTMF signals, the input
amplifier can be muted by applying VMP to G
T
Input for DTMF signals, also used for the answering machine and hands-free input
2
DTMF
3
MICO
Output of microphone preamplifier
4
MIC 2
Non-inverting input of microphone amplifier
5
MIC 1
Inverting input of microphone amplifier
6
PD
Active high input for reducing the current consumption of the circuit, simultaneously V
L
is shorted by an
internal switch
7
IND
The internal equivalent inductance of the circuit is proportional to the value of the capacitor at this pin, a
resistor connected to ground may be used to reduce the DC line voltage
8
VL
Line voltage
9
GND
Reference point for DC- and AC-output signals
10
SENSE
A small resistor (fixed) connected from this pin to V
L
sets the slope of the DC characteristic and also
effects the line-length equalization characteristics and the line current at which the loudspeaker amplifier
is switched on
11
VB
Unregulated supply voltage for peripheral circuits (voice switch), limited to typically 7 V
12
SAO
Output of loudspeaker amplifier
13
VMPS
Unregulated supply voltage for micorcontroller, limited to 6.3 V
14
VMP
Regulated supply voltage of 3.3 V for peripheral circuits (especially microprocessors), minimum output
current: 2 mA (ringing) 4 mA (speech mode)
15
SWOUT
Output for driving external switching transistor
16
COSC
40-kHz oscillator for ringing power converter
17
VRING
Input for ringing signal protected by internal Zener diode
18
THA
Threshold adjustment for ringing frequency detector
19
RFDO
Output of ringing frequency detector
20
LIDET
Line detect; output is low when the line current is more than 15 mA
21
IMPSEL
Control input for selection of line impedance
1.
600
2.
900
3.
Mute of second transmit stage (TXA); also used for indication of external supply (answering
machine); last chosen impedance is stored
22
TSACL
Time constant of anti-clipping of speaker amplifier
23
GSA
Current input for setting the gain of the speaker amplifier, adjustment characteristic is logarithmical, or
RGSA > 2 M , the speaker amplifier is switched off
24
SA I
Speaker amplifier input (for loudspeaker, tone ringer and hands-free use)
25
MUTX
Three-state input of transmit mute:
1.
Speech condition; inputs MIC1/MIC2 active
2.
DTMF condition; input DTMF active. A part of the input signal is passed to the receiving amplifier
as a confidence signal during dialing
3.
Input DTMF used for answering machine and hands-free use; receive branch not affected
26
ATAFS
Attenuation of acoustical feedback suppression, maximum attenuation of AFS circuit is set by a resistor
at this pin, without the resistor, AFS is switched off
27
INLDT
Input of transmit level detector