IL2411
APPLICATION CIRCUIT
F
igure 3
APPLICATION NOTE
The application circuit illustrates the use of the IL2411 devices in typical telephone or extension tone ringer application.
The AC ringer signal voltage appears across the TIP and RING inputs of the circuit and is attenuated by capacitor C1
and resistor R1.
C1 also provides isolation from DC voltages (48V) on the exchange line.
After full wave rectification by the bridge diode, the waveform 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 ouptut frequency chops between 512(fh1) and 640Hz(fh2) at a 10Hz(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 piezo-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 frequency can be determined using the relation fL=1/1.289R2*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=1/1.504R3*C3, fH2=1/1.203R3*C3.
Pin 2 allows connection of an external resistor RSL, which is used to program the solpe of the supply current vs supply
voltage characteristics (see Fig2), 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 couplin capacitors (C5 on Fig 3) (higher impedance) to the
line which can be used to alter the ringer equivalence number of a tone ringer circuit.
The graph in Fig2 illustrates the variation of supply current with supply voltage. Three curves are drawn to show the
variation of initiation current with RSL. Curve B( RSL=6.8KΩ) shows the I-V characteristic for the IL2411 tone ringer.
Curve A is a plot with RSL<6.8KΩ and shows an increase in the current drawn up to the initiation voltageVSI. The I-V
characteristic after initiation remains unchanged. Curve C illustrates the effect of increasing RSL above 6.8KΩ initiation
current decreases but again current after triggering is unchanged.
5
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