6

4872A–CORD–08/05

U4091BM-R

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:

The U4091BM-R contains two identical series regulators which provide a supply voltage VMP of

3.3V 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.

4.

Supply Structure of the Chip

A main benefit of the U4091BM is the easy implementation of various applications due to the

flexible system structure of the chip.

Possible applications:

• Group listening phone

• Hands-free phone

• Phones which feature ringing with the built-in speaker amplifier

• Answering machine with external supply

The special supply topology for the various functional blocks is shown in Figure 4-1 on page 7.

There are four major supply states:

1.

Speech condition

In speech condition, the system is supplied by the line current. If the LIDET block

detects a line voltage above approximately 2V, the internal signal VLON is activated.

This is detected via the serial bus, all the blocks which are needed have to be switched

on via the serial bus.

For line voltages below 2V, the switches remain in quiescent state as shown in the

diagram.

40

AMPB

Input for playback signal of answering machine

41

AMREC

Output for recording signal of answering machine

42

STO

Output for connecting the sidetone network

43

STC

Input for sidetone network

44

STRC

Input for sidetone network

Table 2-1.

Pin Description

Pin

Symbol

Function

Note:

1. The protection device at pin RECIN is disconnected.

L

2R

SENSE

×

C

IND

R

DC

R

30

×

()

×

×

R

DC

R

30

+

()

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