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TP5700AN Arkusz danych(PDF) 6 Page - National Semiconductor (TI) |
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TP5700AN Arkusz danych(HTML) 6 Page - National Semiconductor (TI) |
6 / 8 page Applications Information The TP5700A and TP5700 are flexible circuits designed with several user adjustments to enable the performance to be optimized for different applications The choice of trans- ducer types and the cavities in which they are mounted will also greatly influence the acoustic performance of the tele- phone Some of the consequences of circuit adjustments are as follows RDC ADJUSTMENT 56X is the recommended value for RDC if it is required to meet a maximum Tip-Ring voltage of 45V on a 20 mA loop (assuming no more than 14V is dropped across the polarity guard) If a higher Tip-Ring voltage is acceptable RDC may be increased which will provide a small increase in the available transmit output voltage swing before clipping oc- curs RDC should be less than 82X to avoid exceeding the maximum rated voltage on a short loop RAGC ADJUSTMENT The available AGC range is more than adequate to compen- sate for the loss of most loops RAGC should be chosen only to partly compensate for the anticipated maximum loop loss as over-compensation may tend to exaggerate the var- iations of sidetone with loop length SIDETONE ADJUSTMENT The component values used for ZBAL should be selected to provide a clear sidetone sound without excessive ‘‘hollow- ness’’ The capacitor value and ratio of the two resistors will fix the pole location To avoid reducing the low voltage per- formance of the circuit the sum of the two resistors should not exceed 10 kX POWERING ELECTRET MICROPHONES Electret microphones with integral FET buffers are available in both two-wire and three-wire versions and a range of op- erating voltage ranges There are four methods of powering the microphone 1 The 12V VREG2 output provides the lowest voltage meth- od for microphones rated down to 1V VREG2 must be decoupled with a 1 mF capacitor to ground (See Figure 5 ) 2 If VREG1 is not required for DTMF generator operation it may be used to provide up to 200 mA for microphone power 3 VBIAS (pin 15) may be used as a decoupled but unregu- lated supply for electrets requiring a higher operating voltage than VREG1 or VREG2 The additional current drawn through Ro will however raise the minimum oper- ating voltage of the Speech Circuit If this method is used the decoupling capacitor must be increased to at least 100 mF to maintain good low frequency return loss (See Figure 4 ) 4 An electret type with a good power supply rejection ratio can be powered from Va or a regulated and decoupled supply dropped from Va TONE DIALING TELEPHONE Figure 4 shows the TP5700 directly interfacing to a low volt- age DTMF generator VREG1 supplies the necessary 2V minimum bias to enable the low voltage tone dialer to sense key closures and pull its MUTE output high VREG1 then switches to a 3V regulated output to sustain the Tone Dialer during tone generation The TP5700A DTMF input incorpo- rates the necessary load resistor to Vb and provides gain plus AGC action to compensate for loop length A muted tone level is heard in the receiver For DTMF generators with a higher output level a resistive potentiometer should TLH5201 – 8 FIGURE 4 Typical Tone Dialing Telephone 6 |
Podobny numer części - TP5700AN |
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Podobny opis - TP5700AN |
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