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AS2535T Datasheet(PDF) 6 Page - ams AG |
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AS2535T Datasheet(HTML) 6 Page - ams AG |
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6 / 25 page  6 Rev. 7 July 1998 Data Sheet AS2533...6 Line Loss Compensation The line loss compensation is a pin option. When it is activated, the transmit and receive gains are decreased by 6 dB at line currents from 20 to 50 mA when LLC = A GND and 45 to 75 mA when LLC = high (@ R1 = 30 Ω). The line loss compensation is disabled when LLC = low (see figure 4 and 5). Dialling Functions Valid Keys The key scanning is enabled when HS/DPN is pulled high and V DD is above VREF. A valid key is detected from the keyboard by connecting the appropriate row to the column (R ON < 1 kΩ). This can be done using an n x m keyboard matrix with single contacts. Four diodes are used to extend the number of rows (see keyboard arrangement fig. 2). It is also possible to connect a µcontroller to the rows and columns (see application note AN3010). P/M and MT Key The P/M key (not AS2534E) is used to enter the Programme/Mute state and the MT key for muting (AS2534E only). Depressing the P/M key mutes the speech circuit and the device is in programme state. Repressing the P/M key deactivates the mute and programme state (toggle function).The MT key works in a similar way, but has no programme function. When programme/mute is activated, the LED indication is turned on (flashing: 80 ms 'on' and 1 sec 'off'). Dial Mode Selection The default mode (LD or MF) can be selected by the mode pin. When default LD mode is selected, a temporary change to MF can be invoked by pressing T/P key (not AS2535) or the * key (when mode pin = row 5, the MF tone is generated with the first * key entry). The circuit will revert to LD by repression the T/P key (not AS2535) or by pressing the R (R1, R2 or R3) key or by next on- hook. When MF mode is selected by the mode pin, the circuit can not be changed temporary to LD but will remain in MF mode. Centrex Keys (not AS2535) The alphameric keys accommodate easy use of centrex services. The A, B, C and D keys are only valid in MF mode (including temporary MF) and are not storable. Pressing one of these keys will invoke the appropriate MF tones to be transmitted. The microphone input is differential with an input impedance of 20 k Ω. The soft clip circuit limits the output voltage at LI to 2V PEAK (see figure 12). The attack time is 30 µs/6 dB and the decay time is 20 ms/6 dB. When mute is active, during dialling or after pressing the P/M key, the gain is reduced by > 60 dB. Receive The gain of the receive path is 3 dB for 600 Ω line termination (test circuit figure 10). The receive input is the differential signal of RI and STB. When mute is active during dialling the gain is reduced by > 60 dB. During DTMF dialling a MF comfort tone is applied to the receiver. The comfort tone is the DTMF signal with a level that is -30 dB relative to the line signal. The receive gain can be changed by pressing the volume keys. The VOL key gives a +5.4 dB boost and has a toggle function, i.e. repressing the key resets the gain to default. As an alternative the +/– keys can be used. The + key increases the gain by 8.1 dB in 3 steps and the – key decreases the gain by 5.4 dB in 2 steps (total range 13.5 dB). On AS2533/5 the volume is reset to default by next off-hook and on AS2534/6 the volume setting will remain at last setting. A POR will always reset the volume to default. The soft clip circuit limits the voltage at the receive output (RO) to 1V PEAK (see figure 11). It prevents harsh distortion and acoustic shock. Sidetone A good sidetone cancellation is achieved by using the following equation: ZBAL ZLINE = Z 2 Z 1 The sidetone cancellation signal is applied to the STB input. ZLINE Z1 Z2 ZBAL Figure 3 Side Tone Balance |
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Similar Description - AS2535T |
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