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ISL5586 Folha de dados(PDF) 9 Page - Intersil Corporation |
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ISL5586 Folha de dados(HTML) 9 Page - Intersil Corporation |
9 / 20 page 4-9 The quiescent current terms are specified in the electrical tables for each operating mode. Load power dissipation is not a factor since this is an on hook mode. Some applications may specify a standby current. The standby current may be a charging current required for modern telephone electronics. Standby Current Power Dissipation Any standby line current, ISLC, introduces an additional power dissipation term PSLC. Equation 17 illustrates the power contribution is zero when the standby line current is zero. If the battery voltage is less than -49V (the MTU clamp is off), the standby line current power contribution reduces to Equation 18. Most applications do not specify charging current requirements during standby. When specified, the typical charging current may be as high as 5mA. Forward Active Mode Overview The Forward Active mode (FA, 001) is the primary AC transmission mode of the SLIC. On hook transmission, DC loop feed and voice transmission are supported during this mode. The device may be operated from either high or low battery for on-hook transmission and from low battery for loop feed. Loop supervision is provided by the switch hook detector at the DET output. When DET goes low, the low battery should be selected for DC loop feed and voice transmission. On-Hook Transmission The primary purpose of on hook transmission will be to support caller ID and other advanced signalling features. The transmission over load level while on hook is 3.1VPEAK. When operating from the high battery, the DC voltages at Tip and Ring are MTU compliant. The typical Tip voltage is -4V and the Ring voltage is a function of the battery voltage for battery voltages less than -60V as shown in Equation 19. Feed Architecture The SLIC design implements a voltage feed current sense architecture. The voltage across Tip and Ring is controlled by sensing the load current. Resistors are placed in series with the Tip and Ring outputs to provide the current sensing function. The diagram below illustrates the concept. By monitoring the current at the amplifier outputs, a negative feedback mechanism sets the output voltage for a defined load. The amplifier closed loop gains are set by internal resistor ratios (RA,RB,RC) providing all the performance benefits of matched resistors. The internal sense resistor RCS, is much smaller than the gain resistors and are typically 20 Ω. The feedback mechanism, KS, represents the gain configuration providing negative feedback to the loop. DC Loop Feed The feedback mechanism for monitoring the DC portion of the loop current is contained within the loop detector block. A low pass filter is used in the feedback loop to block voice and other signals from interfering with the loop current limit function. The pole of the low pass filter is set by the external 4.7 µF capacitor (CDC) and an internal 8KΩ resistor. The DC feed characteristic of the SLIC will drive Tip and Ring towards half battery to regulate the DC loop current. For light loads, Tip will be near -4V and Ring will be near VVBL + 4.5V. Most applications will operate the device from low battery while off hook. The following diagram depicts the DC feed characteristic. The point on the y-axis labeled VTR(OC) is the open circuit Tip to Ring voltage and is defined by the feed battery voltage. The curve of Figure 5 shows the loop current for a given set of loop conditions. The loop conditions are determined by the low battery voltage and the DC loop resistance. The DC loop resistance is the sum of the protection resistance, copper resistance (ohms/foot) and the telephone off hook DC resistance. P SL C I SLC V BH 49 – 1I SL Cx1200 ++ () × = (EQ. 17) P SL C I SLC V BH 1I SLC x1200 ++ () × = (EQ. 18) V RING V BH 4.5V + = (EQ. 19) FIGURE 4. VOLTAGE FEED CURRENT SENSE DIAGRAM + - + - VIN VOUT RC RCS RL RB RA KS FIGURE 5. DC FEED CHARACTERISTIC m= ( ∆VTR/∆IL)= 11.1kΩ ILOOP (mA) ILIM VTR(OC) V TR OC () V BL 9 – = (EQ. 20) ISL5586 |
Nº de peça semelhante - ISL5586 |
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Descrição semelhante - ISL5586 |
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