S1T2410B01

The application circuit illustrates the use of the S1T2410B01/B02 devices in typical telephone or extensive tone ringer applications. 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 wave form is filtered by capacitor C4 to provide a DC supply for the tone ringer chip.

When this voltage exceeds the initiation (VSI), oscillation starts.

With the components shown, the output frequency chops between 512 Hz (fH1) and 640Hz (fH2) at a 10Hz (L) rate.ahe loudspeaker load is coupled through a 1300Ω to 8Ω transformer.The output coupling capacitor C5  with transformer coupled loads is required.When driving a piezo-ceramic transducer type load, the coupling C5 and transformer (1300Ω :8 Ω) 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 function fL = 1/(1.289 R2 • C2). The high frequency oscillates at a fH1, fH2controlled by an external resistor (R3) and capacitor (C3). The frequency can be determined using the function  tHI = 1/(1.504 R3 • C3).  Voltage remains constant independent of RSL.

Pin 2 of the S1T2410B02 allows connection of an external resistor RSL, which is used to program the slope of the supply current vs supply voltage characteristics (see Fig. 2) and hence the supply current up to the initial voltage (VSI). This initial voltage remains constant independent of RSL.The supply current drawn prior to triggering is inversely proportional with RSL, decreasing for an increasing value of resistance.

Thus, increasing the value of RSL, will decrease the amount of AC ringing current required to trigger the device. Longer subscriber 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 compensate for smaller AC coupling capacitors (C
5 on Fig. 3) (higher impedance) to the line which is used to alter the ringer equivalence number of a tone ringer circuit.

The graph in Fig. 2 illustrates the variation of supply current with supply voltage of the S1T2410B02. Three curves are drawn to show the variation of the initiation current with RSL. Curve B (RSL = 6.8kΩ) shows the I-V characteristic for the S1T2410B02 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. After initiation, the I-V characteristic remain unchanged. Curve C illustrates the effect of increasing RSL above 6.8kΩ initiation current decreases, but is unchanged after triggering.