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PBL386402SOT Datasheet(PDF) 11 Page - Ericsson |
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PBL386402SOT Datasheet(HTML) 11 Page - Ericsson |
11 / 16 page PBL 386 40/2 11 Figure 10. Hybrid function. When choosing R TX, make sure the output load of the VTX terminal is >20 k Ω. If calculation of the Z B formula above yields a balance network containing an inductor, an alternate method is recom- mended. Contact Ericsson Microelectron- ics for assistance. The PBL 386 40/2 SLIC may also be used together with programmable CODEC/filters. The programmable CODEC/filter allows for system controller adjustment of hybrid balance to accom- modate different line impedances without change of hardware. In addition, the transmit and receive gain may be ad- justed. Please, refer to the programm- able CODEC/filter data sheets for design information. Longitudinal Impedance A Feed back loop counteracts longitudi- nal voltages at the two-wire port by injecting longitudinal currents in opposing phase. Thus longitudinal disturbances will appear as longitudinal currents and the TIPX and RINGX terminals will experi- ence very small longitudinal voltage excursions, leaving metallic voltages well within the SLIC common mode range. The SLIC longitudinal impedance per wire, Z LoT and ZLoR, appears as typically 20 Ω to longitudinal disturbances. It should be noted that longitudinal currents may exceed the dc loop current without disturbing the vf transmission. Capacitors C TC and CRC The capacitors designated C TC and CRC in figure 12, connected between TIPX and ground as well as between RINGX and ground, can be used for RFI filter- ing.. The recommended value for C TC and C RC is 2200 pF. Higher capacitance values may be used, but care must be taken to prevent degradation of either longitudinal balance or return loss. C TC and C RC contribute to a metallic imped- ance of 1/( π·f·C TC) = 1/(π·f·CRC), a TIPX to ground impedance of 1/(2· π·f·C TC) and a RINGX to ground impedance of 1/ (2· π·f·C RC). AC - DC Separation Capacitor, C HP The high pass filter capacitor connected between terminals HP and TIPX provides the separation of the ac signal from the dc part. C HP positions the low end VT Combination CODEC/Filter RTX RFB ZB ZRX ZT VTX RSN VRX PBL 386 40/2 frequency response break point of the ac loop in the SLIC. Refer to table 1 for recommended values of C HP. Example: A C HP value of 150 nF will position the low end frequency response 3dB break point of the ac loop at 1.8 Hz (f 3dB) according to f3dB = 1/(2·π·RHP·CHP) where R HP = 600 kΩ. High-Pass Transmit Filter The capacitor C TX in figure 12 connected between the VTX output and the CODEC/filter forms, together with R TX and/or the input impedance of a pro- grammable CODEC/filter, a high-pass RC filter. It is recommended to position the 3 dB break point of this filter between 30 and 80 Hz to get a faster response for the dc steps that may occur at DTMF signalling. Capacitor C LP The capacitor C LP, which connects between the terminals CLP and VBAT, positions together with the resistive loop feed resis- tor R SG (see section Battery Feed), the high end frequency break point of the low pass filter in the dc loop in the SLIC. C LP together with R SG, CHP and ZT (see section Two-Wire Impedance) forms the total two wire output impedance of the SLIC. The choise of these programmable components have an influence on the power supply rejection ratio (PSRR) from VBAT to the two wire side at sub-audio frequencies. At these frequencies capacitor C LP also influences the transversal to longitudinal balance in the SLIC. Table 1 suggests suitable values on C LP for different Feeding characteristics. Typical values of the transversal to longitu- dinal balance (T-L bal.) at 200Hz is given in table 1 for the chosen values on C LP. R Feed R SG C LP T-L bal. C HP @200Hz [ Ω][kΩ] [nF] [dB] [nF] 2 ⋅50 0 150 -46 47 2 ⋅200 60.4 100 -46 150 2 ⋅400 147 47 -43 150 2 ⋅800 301 22 -36 150 Table 1. R SG , CLP and CHP values for different Feeding characteristics. |
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