U4090B-P Datasheet, PDF (13/35 Pages) ATMEL Corporation – Monolithic Integrated Feature Phone Circuit EMI Improved

Figure 3-9. Line Detection in Speech Mode with Hysteresis
LIDET
U4090B-P
ILOFF
ILON
IL
3.4 Ringing Power Converter (RPC)
The RPC transforms the input power at VRING (high voltage/low current) into an equivalent out-
put power at V_B (low voltage/high current) which is capable of driving the low-ohmic
loudspeaker. Input impedance at VRING is fixed at 5 kΩ and the efficiency of the step-down con-
verter is approximate 65%.
Figure 3-10. Comparator Thresholds Depending on DC Mask and Line Impedance
7
R_DC = ∞
6
R_DC = 130 kΩ
5
4
R_DC = 68 kΩ
3
10 12
14
16
18 20
I_L (mA)
= ILON _{at line impedance = 600Ω}
= ILOFF
=
=
ILON
ILOFF
at
line
impedance
=
900Ω
3.5 Ringing Frequency Detector (RFD)
The U4090B-P offers an output signal for the microcontroller, which is a digital representation of
the double ringing frequency. It is generated by a current comparator with hysteresis. The input
voltage V_RING is transformed into a current via RTHA. The thresholds are 8 µA and 24 µA. RFDO
and V_RING are in phase. A second comparator with hysteresis is used to enable the output RFDO
as long as the supply voltage for the microprocessor VMP is above 2.0V.
13
4741C–CORD–11/05