AN1500A South African Micro-Electronic Systems, AN1500A Datasheet - Page 17

• Manufacturer Part Number: AN1500A
• Description: Single Chip Telephone Demo Board
• Manufacturer: South African Micro-Electronic Systems

Make pulses are performed by Q3 with Q1 being switched on. The base of Q3 (=pin CS, #25) is pulled to V
resulting in V
CS is pulled low during the complete dialing period of one digit, which means in worst case (dialing number “0”) the
circuit cannot be supplied from line and must be buffered by the V
supply the active circuit for 1 second.
15.6 Pre-digit, Inter-digit ,inter-tone and access pauses
During pulse and DTMF dialing, several pauses must be added (see also: data sheet):
The following tables give an overview of the advantages and disadvantages of 3 different types of hook transistor
arrangements: single bipolar PNP, PNP darlington and MOSFET. Any of these configurations can be installed on
the demo board. Just check for corresponding part name on the PCB layout.
16.1 electrical requirements
Both hook transistor (Q1) and driver transistor (Q2) must be >=200V types, Q1 must have an IC >100mA. If single
PNP configuration is used, the transistor must have a gain
have enough gain to be in full saturation at high line currents ( if driving a bipolar hook transistor ).
recommended types:
2SA1210, MPSA92,BSS92 (depending on configuration)
BSP92 (SMD)
KSA1156Y
16.2 Single bipolar transistor
Schematic
16 Hook Transistor options
17/27
pre-digit pause (PDP):
inter-digit pause (IDP):
inter-tone pause (ITP):
access pause (AP):
AN1500A
LI
= V
BE
0.7V.
Q1
Pause between CS=low and first break (pulse dialing only)
Pause between pulse dialed out numbers, from last “make” to next PDP
Pause between DTMF dialed out numbers
manually inserted pause in a digit string (see pt. 7.8)
sames
sames
sames
sames
lowest DC mask at low currents
just one transistor
+
IC
IB
100
DD
-cap, C9. Therefore C9 must be big enough to
at I
C
=100mA. The driver transistor (Q2) must
BF820 (SMD)
Transistor type must have a gain
high on-resistance at high
currents slightly affects gains and
DTMF level
10k
AC impedance
IC
IB
MPSA43
2N5551
Q2
100
base resistor (R4) affects
at I
C
=100mA
-
SS
,