SL2411
APPLICATION NOTE
The application circuit illustrates the use of the SL2411 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 1300W to 8W 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 (1300W:8W) 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=1/1.289R2xC2. 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=1/1.504R3xC3, fH2=1/1.203R3xC3.
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=6.8KW) shows the I-V characteristic for the SL2411 tone
ringer.
Curve A is a plot with RSL<6.8KW and shows an increase in the current drawn up to the initiation voltageV . The
SI
I-V characteristic after initiation remains unchanged. Curve C illustrates the effect of increasing RSL above 6.8KW
initiation current decreases but again current after triggering is unchanged.
System Logic
SLS
Semiconductor
SLS [ SYSTEM LOGIC SEMICONDUCTOR ]
