U4091BM-N Datasheet, PDF (6/38 Pages) ATMEL Corporation – PROGRAMMABLE TELEPHONE AUDIO PROCESSOR

Pin Description
Pin
Symbol Function
39
MICO Microphone preamplifier output
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
Note: 1. The protection device at Pin RECIN is disconnected.
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----^×------^R-----^S---^E---^N---^S---^E-----^×------^C----^I--^N---^D-----^×------⁽--^R-----^D---^C-----^×------^R----³---⁰---⁾
(R_DC + R₃₀)
The U4091BM-N 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 suffi-
cient 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.
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 illustrated in Figure 4 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 2 V, the internal signal VLON is acti-
vated. 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 2 V, the switches remain in quiescent state as shown in
the diagram.
2. Power down (pulse dialing):
When the chip is in power-down mode (Bit LOMAKE), e.g., during pulse dialing,
all internal blocks are disabled via the serial bus. In this condition, the voltage
regulators and their internal band gap are the only active blocks.
6 U4091BM-N
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