7

4872A–CORD–08/05

U4091BM-R

2.

Power down (pulse dialing)

When the chip is in power-down mode (bit LOMAKE), for example, during pulse dialing,

all internal blocks are disabled via the serial bus. In this condition, the voltage regula-

tors and their internal band gap are the only active blocks.

3.

Ringing

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.

External supply

In an answering machine, the chip is powered by an external supply via pin VB. The

answering machine connections can be directly made to U4091BM-R. The answering

machine is connected to the pin AMREC. For the output AMREC, an AGC function is

selectable 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. This enables the sig-

nal to be switched to every desired output.

Figure 4-1.

Supply Generator

5.

Ringing Power Converter (RPC)

The RPC transforms the input power at VRING (high voltage/low current) into an equivalent out-

put 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

Ω to 12 kΩ by R

IMPA

(Z

6.

Ringing Frequency Detector (RFD)

The U4091BM-R provides an output signal for the microcontroller. This output signal is always

double the value of the input signal (ringing frequency). It is generated by a current comparator

with hysteresis. The levels for the on-threshold are programmable in 16 steps, the off-level is

fixed. Every change of the comparator output generates a high level at the interrupt output INT.

The information can then be read out by means of a serial bus with either normal or fast read

mode. The block RFD is always enabled.

+

-

-

+

3.3V

5.5V

5.5V

V

470 µF

300 k

Ω

-

+

R

47 µF

220 µF

1 µF

10

R

IND

C