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TEA1113T 데이터시트(PDF) 6 Page - NXP Semiconductors |
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TEA1113T 데이터시트(HTML) 6 Page - NXP Semiconductors |
6 / 20 page 1997 Mar 27 6 Philips Semiconductors Product specification Low voltage versatile telephone transmission circuit with dialler interface TEA1113 The internal circuitry of the TEA1113 is supplied from pin VCC. This voltage supply is derived from the line voltage by means of a resistor (RCC) and must be decoupled by a capacitor CVCC. It may also be used to supply peripheral circuits such as dialling or control circuits. The VCC voltage depends on the current consumed by the IC and the peripheral circuits as shown by the formula (see also Figs 5 and 6). RCCint is the internal impedance of the voltage supply point, and Irec is the current consumed by the output stage of the earpiece amplifier. The DC line current flowing into the set is determined by the exchange supply voltage (Vexch), the feeding bridge resistance (Rexch), the DC resistance of the telephone line (Rline) and the reference voltage (Vref). With line currents below 8 mA, the internal reference voltage (generating Vref) is automatically adjusted to a lower value. This means that more sets can operate in parallel with DC line voltages (excluding the polarity guard) down to an absolute minimum voltage of 1.6 V. At currents below 8 mA, the circuit has limited sending and receiving levels. This is called the low voltage area. V CC V CCO R CCint I p I rec – () × – = V CCO V LN R CC I CC × – = handbook, halfpage PERIPHERAL CIRCUIT IP Irec RCCint VCC VEE VCCO MBE792 Fig.5 VCC voltage supply for peripherals. Set impedance In the audio frequency range, the dynamic impedance is mainly determined by the RCC resistor. The equivalent impedance of the circuits is illustrated in Fig.7. LED supply (pin ILED) The TEA1113 gives an on-hook/off-hook status indication. This is achieved by a current made available to drive an LED connected between pins ILED and LN. In the low voltage area, which corresponds to low line current conditions, no current is available for this LED. For line currents higher than a threshold current, the ILED current increases proportionally to the line current (with a ratio of one third).The ILED current is internally limited to 19.5 mA (see Fig.8). For 17 mA < Iline < 77 mA: This LED driver is referenced to SLPE. Consequently, all the ILED supply current will flow through the RSLPE resistor. The AGC characteristics are not disturbed (see Fig.3 for the supply configuration). Microphone amplifier (pins MIC +, MIC− and GAS) The TEA1113 has symmetrical microphone inputs. The input impedance between pins MIC + and MIC− is 64 k Ω (2 × 32 kΩ). The voltage gain from pins MIC+/MIC− to pin LN is set to 51.8 dB (typ). The gain can be decreased by connecting an external resistor RGAS between pins GAS and REG. The adjustment range is 13 dB. A capacitor CGAS connected between pins GAS and REG can be used to provide a first-order low-pass filter. The cut-off frequency corresponds to the time constant CGAS × (RGASint // RGAS). RGASint is the internal resistor which sets the gain with a typical value of 69 k Ω. Automatic gain control is provided on this amplifier for line loss compensation. Dynamic limiter and microphone mute (pin DLS/MMUTE) The dynamic limiter only acts on the microphone channel, this is to prevent clipping of the line signal. To prevent distortion, the microphone gain is rapidly reduced when peaks on the line signal exceed an internally determined threshold level or when the current in the transmit output stage is insufficient. The time in which the gain reduction is realized is very short (attack time). The microphone channel stays in the reduced gain condition until the peaks I LED I line 17 – 3 ---------------------- = |
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