AN1500A South African Micro-Electronic Systems, AN1500A Datasheet - Page 16

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

lowered by only 0.2V for line currents >17mA. At lower line currents however, as required for these countries, the
DC mask is lowered significantly, since slope-down of LI occurs already at line currents <17mA..
Fig.10 shows a typical example for a low DC mask setting compared with the DC-mask specs for Denmark (ETS
300 001: March 1996) : the solid line indicates the DC mask with a 16k
line shows the DC mask of the original AN1500 A0 version with a single PNP hook transistor (ref. pt.16).
Note: When connecting a resistor at CI, AC impedance, DTMF level, Tx/Rx gains and LLC gain curves are slightly
changed. Therefore, after installing a resistor at CI, the above parameters must be readjusted.
15.3 Speech mode
In speech mode, shunt regulation (by Q3) is active and line current flows as described in pt 15.1. At the same time,
both Tx and Rx amplifiers and 2 wire-4 wire conversion circuits are active.
15.4 DTMF dialing
During DTMF dialing the same line conditions as in Speech mode apply, except that speech is muted in both
directions and a confidence tone is sent to the Rx amplifier.
The DTMF signal is modulated to the line by controlling the shunt transistor, Q3. During inter-digit pauses speech is
also muted.
15.5 Pulse dialing
With pulse dialing, the line has to be interrupted during “break” periods and short circuited during “make” periods.
For example, “LD 60/40 10pps” means: break/make ratio is 60:40 with 10 pulses per second =
The dialing pulse is a 60ms break (line interrupt) followed by a 40ms make (line short circuit).
Dialing number “1” will result in one dialing pulse, total time = 100ms.
Dialing number “0” will result in 10 dialing pulses, total time = 10*100ms = 1sec.
Line break pulses are performed by Q1 being switched off. The on-off control signal is output from the HS/DP pin
(#10) switching Q2 (and in turn Q1) on and off.
16/27
AN1500A
15
13
11
-1
9
7
5
3
1
0
5
10
sames
sames
sames
sames
Fig. 9 : Example for low DC mask: Denmark
15
I line [mA]
DC mask: Denmark
20
25
30
35
resistor connected at CI, while the dotted
40
CI = 16k
CI = n.c.
DC mask UL
DC mask LL