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U3900BM Datasheet(PDF) 12 Page - TEMIC Semiconductors |
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U3900BM Datasheet(HTML) 12 Page - TEMIC Semiconductors |
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12 / 34 page  U3900BM Rev. A2, 25-Aug-98 Target Specification 12 (34) 3 DC Line Interface and Supply-Voltage Generation The DC line interface consists of an electronic inductance and a dual-port output stage which charges the capacitors at VMPS and VB. The value of the equivalent inductance is given by: L = 2 RSENSE CIND (RDC R30) / (RDC + R30) The U3900BM contains two identical series regulators which provide a supply voltage VMP of 3.3 V suitable for a microprocessor. In speech mode, both regulators are active because VMPS and VB are charged simultaneously by the DC-line interface. The output current is 6 mA. The capacitor at VMPS is used to provide the microcomputer with sufficient power during long line interruptions. Thus, long flash pulses can be bridged or an LCD display can be turned on for more than 2 seconds after going on-hook. When the system is in ringing mode, VB is charged by the on–chip ringing power converter. In this mode, only one regulator is used to supply VMP with maximum 3 mA. 3.1 Supply Structure of the Chip As main benefit of the U3900BM is the easy implementa- tion of various applications due to the flexible system structure of the chip. Possible applications: D Group listening phone D Hands-free phone D Phones which feature ringing with the built-in speaker amplifier D Answering machine with external supply The special supply topology for the various functional blocks is illustrated in figure 11. There are four major supply states: 1. Speech condition 2. Power down (pulse dialing) 3. Ringing 4. External supply 1. In speech condition, the system is supplied by the line current. If the LIDET-block detects a line voltage above approximately 2 V, the internal signal VLON is activated. This is detected via serial bus, all necessary the blocks have to be switched on via the serial bus. For line voltages below 2 V, the switches remain in quiescent state as shown in the diagram. 2. When the chip is in power-down mode (Bit LOMAKE), e.g., during pulse dialing, all internal blocks are disabled via the serial bus, except the oscillator. In this condition, the voltage regulators and their internal bandgap are the only active blocks. 3. During ringing, the supply for the system is fed into VB via the Ringing Power Converter (RPC). Normally, the speaker amplifier in single-ended mode is used for ringing. The frequency for the melody is generated by the DTMF/Melody generator. 4. In an answering machine, the chip is powered by an external supply via Pin VB. The answering machine connections could be directly put to U3900BM. The answering machine is connected to the Pin AMREC. For the output AMREC, an AGC function is select- able via the serial bus. The output of the answering machine will be connected to the Pin AMPB, which is directly connected to the switching matrix, and thus enables the signal to be switched to every desired output. 14573 + – – + 3.3 V 5.5 V VMPS VMP 5.5 V V 470 µF 300 k Ω – + R 47 µF 220 µF 1 µF 10 Ω RSENSE R IND C VL VB Figure 12. Supply generator 4 Ringing Power Converter (RPC) The RPC transforms the input power at VRING (high voltage/ low current) into an equivalent output power at VB (low voltage/ high current) which is capable of driving the low-ohmic loudspeaker. The input impedance at VRING is adjustable from 3 k W to 12 kW by RIMPA (ZRING = RIMPA / 100) and the efficiency of the step- down converter is approximately 65%. |
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