U4090B-P Datasheet, PDF (12/35 Pages) ATMEL Corporation – Monolithic Integrated Feature Phone Circuit EMI Improved

Figure 3-7. Reducing Speaker Amplifier Gain Results in an Equal Reduction of AFS
Attenuation
ATAFS (dB)
ATAFS_m
ATAFS_a
R_ATAFS
R_ATAFS
not usable
GSA_o
GSA_a
36 dB _{GSA (dB)}
Figure 3-8. Line Detection with Two Comparators for Speech Mode and Pulse Dialing
IL
LIDET
PD
3.3 Line Detection (LIDET)
The line current supervision is active under all operating conditions of the U4090B-P. In speech
mode (PD = inactive), the line-current comparator uses the same thresholds as the comparator
for switching off the entire speaker amplifier. The basic behavior is illustrated in Figure 3-9 on
page 13. Actual values of ILON/ILOFF vary slightly with the adjustment of the DC characteristics
and the selection of the internal line impedance.
When Power Down is activated (during pulse dialing), the entire line current flows through the
short-circuiting transistor QS (see Figure 3-3 on page 8). As long as IL is above typically 1.6 mA,
output LIDET is low. This comparator does not use hysteresis.
12 U4090B-P
4741C–CORD–11/05