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L7590C Datasheet(PDF) 4 Page - Agere Systems |
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L7590C Datasheet(HTML) 4 Page - Agere Systems |
4 / 10 page 4 4 Lucent Technologies Inc. Data Sheet June 1998 L7590C Telephone Ringing Driver Functional Description Ringer Requirements This discussion highlights some of the requirements in the United States and Germany. Beginning with the telephone set ringer to be powered, the United States requires 40 Vrms to be delivered to the equivalent of five parallel telephone sets, or 5 REN (Ringer Equiva- lence Number), that translates to 1386 Ω + 40 µF. In Germany, 30 mApeak must be delivered to four parallel telephone sets. In Germany, 4 REN have an imped- ance of 450 Ω + 3.4 µF. The difference results from the impedance of the telephone-set ringers of the two countries. Ringing Requirements In Germany, both single-ended ringing and balanced ringing can be used. This is not so in the United States, where some ringers on older equipment have a ground connection at the telephone set, and the signal lead is either the Tip or Ring wire of the twisted pair. This has led to the recommended use of single-ended ringing. Both administrations allow ringing with a negative dc level, known as battery-backed ringing, but in the United States, there is a constraint that this level can- not be more negative than –75 V. With the exception of the United States, most world- wide administrations require an injection of a pure sine wave. Depending on the country, the distortion require- ment is in the range of 3% to 5%. In the United States, the wave does not need to resemble a sine wave, but it cannot be a square wave. The shape requirement of the wave in the United States is expressed as a crest factor (c.f.). This is the ratio of the peak to the rms volt- age of the signal. The requirement is 1.2 < c.f. < 1.6. Operation On the L7590C, the prefiltered output is a high- voltage replica of the PWM digital signal that is applied to the CLK input. The signal at OUT is produced by level shifting and control of the high-voltage transistors. The level is determined by the magnitude of the nega- tive dc voltage applied to the output stage transistors. The output, ideally, should be an exact time replica of the CLK input to faithfully reproduce the modulating waveform. This high-voltage replica of the CLK input is filtered to leave only the low-frequency, high-voltage sine wave ringing signal. Figure 3, parts A and B, illus- trates the PWM signal with relation to the modulating signal frequency. The PWM signal is at a 100 kHz rate and modulated at the desired ringing signal frequency, typically 20 Hz to 30 Hz. Laboratory equipment genera- tion of the required signal is shown in Figure 5. Propa- gation delays and switching parameters associated with the control circuitry and output stage transistors can cause skewing which will produce a distorted out- put of the modulating waveform. Skewing is illustrated in Figure 4, parts A, B, and C. The skewing can be seen as an increase in the duty cycle of the L7590C output compared to the input signal duty cycle. Using the test arrangement as shown in Figure 5, the harmonic distortion of the filtered output of the L7590C was measured with two different loading circuits. With the North American 5 REN (1386 Ω + 40 µF) load, the THD was typically 2.0% to 2.5%. With the Germany 4 REN (450 Ω + 3.4 µF) load, the THD was typically 1.5% to 2.0%. The 25 Hz output of the HP* 3311A generator showed a typical THD of 1.5% when supply- ing a signal to the HP 8116A. A 20 Ω resistor (RILIM) must be added between L1 and OUT for 5 REN loads. * HP is a registered trademark of Hewlett-Packard Company. |
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