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SA2531J Datasheet(PDF) 4 Page - Sames |
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SA2531J Datasheet(HTML) 4 Page - Sames |
4 / 24 page 4/24 SA2531 A/B/C/E/G/U sames FUNCTIONAL DESCRIPTION Power On Reset The on chip power on reset circuit monitors the supply voltage (V DD). When VDD rises above approx. 1.2V, a power on reset occurs to assure correct start-up and the RAM is cleared. DC Conditions The normal operating range is from 13mA to 100 mA. Operating range with reduced performance is from 5mA to 13mA. In the operating range all functions are operational. At line currents below 13mA the SA2531 provided an additional scope below 4.5V to allow parallel operation. (See Figure 12). The dc characteristic (excluding diode bridge and Pulsing transistors) is determined by the voltage at LI and the resistor R1 as follows: VLS = VLI + I Line.R1 The voltage at LI is 4.5V. During pulse dialling the speech circuit and other parts of the device not required are in a power down mode to save current. The CS pin is pulled to V SS in order to turn the external shunt transistor on to keep a low voltage drop at the LS pin during make periods. AC Impedance The Characteristic or Output impedance of the SA2531 is set within the IC and adjusted by Mask Options. Available options are for 600 Ω and 1000Ω. When the 1000Ω option is selected then a capacitor may be added to the circuit at pin CI to add a reactive element and make the output impedance complex. Oscillator All the Timing Functions of the SA2531 are based on a Clock Frequency of 3.58MHz. A crystal or ceramic resonator of this frequency should be connected to the OSC pin. In practise minor deviations from the nominal frequency may occur due to the characteristics of the frequency reference device used and so it is recommended that care is taken in the selection of components. Typically a small value capacitor ( ≤47pF) should be connected in parallel with the Frequency Reference to ensure start-up and/or operation at the nominal frequency. Speech Circuit The speech circuit consists of a transmit and a receive path born with soft clip, mute, line loss compensation and side tone cancellation. Transmit The gain of the transmit from M1/M2 to LS is 35dB for 600 Ω versions and 37dB for 1000Ω versions (see test circuit figure 5). The microphone input is differential with an input impedance of 25 k Ω. The soft clip circuit limits the output voltage at LI to 2.0V PEAK (see figures 8 & 9). The attack time is 30µs/6dB and the decay time is 20 ms/6 dB. When mute is active, during dialling |
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