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UTCTA31002

Telephone tone ringer

Unisonic Technologies 

UTC 31002A LINEAR INTEGRATED CIRCUIT

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 (FH1) and 640

Hz(FH2) at a 10 Hz(FL) rate.

The loudspeaker load is coupled through a 1300Ω

to 8Ω 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 (1300Ω:8Ω)

are not required.

However, a current limiting resistor is required.

The low frequency oscillator oscillates at a rate (FL)

controlled by an external resistor (R2) and capacitor

(C2).

The fequency can be determined using the

relation FL=1/1.289 R2* C2. The high frequency

oscillates at a FH1,FH2 controlled by an external

resistor (R3) and capacitor (C3). The frequency can

be determined using the relation FH1=1/1.504 R3*C3

and FH2=

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<6.8KΩ

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.

UTC UNISONIC TECHNOLOGIES CO., LTD. 3

QW-R108-005,A

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