MT88E45BNR Zarlink, MT88E45BNR Datasheet - Page 9

• Manufacturer Part Number: MT88E45BNR
• Description: Caller ID CMOS 3.58MHz 3.3V 20-Pin SSOP T/R
• Manufacturer: Zarlink

Specifications of MT88E45BNR

• Package: 20SSOP
• Telecommunication Standards Supported: ANSI/TIA/EIA-716|ETSI/ETS 300 778-1|GR-30|SIN227|SIN242|SR-TSV-002476|TIA/EIA-777
• Fabrication Technology: CMOS
• Maximum Data Rate: 1212 Bd
• Typical Operating Supply Voltage: 3.3 V
• Typical Supply Current: 2.8 mA
• Minimum Operating Temperature: -40 °C
• Maximum Operating Temperature: 85 °C
• Operating Frequency: 3.58 MHz

MT88E45
dropouts once EST has met the minimum tone
duration so as to decrease the likelihood of a long
talkoff being broken up into several talkoffs. Usually
t
there is another way to deal with the problem (by
ignoring further detections for 2 seconds after every
detection).
Tone present guard time (t
initially there is no CAS, EST is low so Q1 is off. C
has been fully charged applying 0V to ST/GT so Q2
is on. When both tones are detected EST goes high
and turns off Q2. Because C has been fully charged
(ST/GT=0V), the comparator output is low and Q1
stays off. With both Q1 and Q2 off the high at EST
discharges C through R1 and the ST/GT voltage
increases from 0V. When the voltage exceeds the
comparator threshold VTGt, which is typically 0.5
Vdd, the comparator output goes high; Q1 turns on
and accelerates the discharge of C (ST/GT goes
quickly to Vdd); STD goes low to indicate that a valid
CAS has been received. If one or both tones
disappeared before t
ST/GT voltage is still below VTGt), Q2 turns back on
8
GA
is set very short or removed altogether because
CAS
EST
ST/GT
STD
Both Tones Present
GP
has been reached (i.e. when
t
DP
GP
t
) operation: In Figure 5
GP
Figure 5 - CAS Guard Time Circuit Operation
t
REC
Comparator
+
-
t
DA
t
GA
and charges C quickly to bring the ST/GT voltage
back to 0V. Then if EST goes high again the t
duration must start over.
Tone absent guard time (t
initially both tones have been detected for t
fully discharged and ST/GT is at Vdd. While both
tones continue to be detected EST stays high; ST/GT
is at Vdd (the comparator output is high); so Q1 is on
and Q2 is off. When one or both tones stop EST
goes low and turns off Q1. Because C is fully
discharged (ST/GT=Vdd), the comparator output is
high and Q2 stays off. With both Q1 and Q2 off the
low at EST charges C through Rp=(R1 || R2) and the
ST/GT voltage falls towards 0V. When the voltage
has fallen below VTGt, the comparator output goes
low. Since EST is also low Q2 turns on and
accelerates the charging of C so that ST/GT goes
quickly to 0V. STD goes high to indicate that the CAS
has ended. If EST goes back to high before t
been reached (i.e. when ST/GT voltage is still above
V
bring the ST/GT voltage back to Vdd. Then if EST
TGt
VTGt
t
ABS
), Q1 turns back on and discharges C quickly to
P
N
Q2
Q1
= Vss
MT88E45
t
t
Rp=R1 || R2
t
GP
GA
GA
=R1C ln [Vdd / (Vdd-VTGt)]
=RpC ln
=0 if R2=0
Advance Information
GA
ST/GT
EST
Vdd
DR
Indicates STD in CAS
detection mode
R1
) operation: In Figure 5
VTGt - Vdiode (Rp/R2)
Vdd - Vdiode (Rp/R2)
Rp=R1 || R2
/
STD
C
R2
V
diode
GP
so C is
GA
has
GP