UTCL6726

LINEAR INTEGRATED CIRCUIT

8

QW-R108-015,A

resistors R4 and R5 must not be less than 35 kΩ because of DC-current to ground. Below is some simple variations

of this network. (See figure 7).

DC-characteristics (R6):

Sets the DC-characteristic and take care of some of the supplied power. The resistor have also function with the

protection of the circuit, the transmitter, the gain regulation and side tone. Common values are 47 Ω to 100 Ω.

Side tone level, receiving gain and frequency response.(R7,R8,R9,R10,R11,C5):

The network sets the side tone balance. The network in the application is one of many possibilities. R10 and R11

balance together the signals that go two different ways from the transmitter output stage one from pin1 and the other

from pin2. The balance network consist of R8, R9 and C5.

The example is not optimized to any specified line, it is only given to show the principle.

Fig8, 9 and 10 are examples of balance networks. Fig.10 is especially suited for lines with high current supply.

R12, R13, C6, (R10, R11):

The networks gives the gain and frequency response for the receiver.

Input impedance at pin 15 is about 38 kΩ with a typical variation of ±20%.For different possibilities for the design

of the network, see the network for the transmitter (R4, R5, C3)

REC, R14:

R14 generates the output impedance to the magnetic earphone (fig.11). If a dynamic earphone is used it should

be placed between pin 17 and 18.See figure 16.

R15:

This resistor is used to set the driving capability of the receiver output amplifier. Common values are 0 Ω to 50 Ω.

Setting it for low driving capability results in function at lower line current. Breaking up pin 16 will give lower power

consumption and total mute of the receiver when muting the circuit. Disconnecting pin 15 will of cause also give total

receiver mute.

D1, D2, D3, D4, D5:

Rectifier bridge and over voltage protector. The zener voltage at D5 should be as low as possible. Common values

are between 12V~16V.

Refer to figure 5.

The pre-set output voltage of 2.35V can easily, if needed, be changed to another value by applying one or two

voltage and current from the DC-supply as long as the high current and voltage is available from the line. The DC

voltage has to be filtered by a capacitor and this can, at high DC-voltage and low line current, interfere with the

signal on the line and cause distortion. You can minimize the interference, with a resistor in series with the filter

capacitor. The DC voltage will, of course, be more dependent of the DC-supply current. The DC-output pin has a

very low input leak current, to allow stand-by feeding of the dialer. It is also possible to use pin 9 to feed

microphones etc. that do not need stand-by feeding, without interfering with the stand-by feeding on pin 8. Note that

a high current consumption by the external device will alter the DC characteristics of the speech circuit