UTC31002A

LINEAR INTEGRATED CIRCUIT

3

QW-R108-005,A

APPLICATION NOTE

The application circuit illustrates the use of the UTC

31002A device in typical telephone tone ringer

application.

The AC ringer

signal

voltage

appears

across

the TIP and

RING

inputs of the circuit and

is attenua-

ted by capacitor C1 and resistor R1.

C1 also provides isolation from DC voltage (48V)

on the exchanged line.

After full

wave

rectification

by

the bridge

diode, the wave form is filtered by capacitor C4 to

provide a DC supply for the tone ringer chip.

As this voltage exceeds the initiation voltage (Vsi),

oscillation starts.

With the components shown , the output frequency

chops between

512Hz

and 640

The loudspeaker load is coupled through a 1300

Ω

to 8

Ω transformer.

The output coupling capacitor C5 is required with

transformer coupled loads.

When driving a pizeo-ceramic transducer type load,

the coupling C5 and transformer

(1300

Ω:8Ω) are

not required.

However, a current limiting resistor is required.

controlled by an external resistor (R2) and capacitor

(C2).

The fequency can be determined using the relation

high

frequency

oscillates

at

(R3)

and capacitor (C3). The frequency can be determined

1/1.203 R3*C3.

Pin 2 of the UTC 31002A allows connection of

external resistor RSL, which is used to program the

slope

of

the supply current vs. supply voltage

characteristics (see Fig.3),

and hence

the

supply

current up to the initiation voltage (Vsi). This initiation

voltage remains constant independent of

RSL.

The supply current drawn prior to triggering varies

inversely with RSL, decreasing for increasing value

of resistance. Thus, increasing the value of RSL, will

decrease the amount of AC ringing current required to

trigger the device. As such, longer sucribser loops are

possible since less voltage is dropped per unit length of

loop wire due to the lower current level. RSL can

also be used to compensated for smaller

AC coupling

capacitors (C5 on Fig.4) (higher impedance) to

the

line which can

be used

to alter the ringer

equivalence

number of a tone ringer circuit.

The graph in Fig.3 illustrates the variation of supply

current

with

supply

voltage of

the UTC 31002A.

Three curves are drawn to show the variation of

initiation

current with

RSL.

Curve B

( RSL=6.8K)

shows the

I-V characteristic

for

UTC 31002A

tone

ringer.

Curve A is a plot

with

RSL<6.8K

Ω

and shows an increase in the current drawn

up to the

initiation voltage Vsi. The I-V characteristic after

initiation remains

unchanged.

Curve C illustrates the

effect

of

increasing

RSL

above

6.8K

initiation

current

decreases

but

again

current

alter triggering is unchanged.