TISP8200M & TISP8201M
APPLICATIONS INFORMATION
Operation of SLICs using Positive and Negative Voltage Supply Rails
Figure 3 shows a typical powering arrangement for a multi-supply rail SLIC. VBATR is a positive supply and VBATL and VBATH are negative
supplies. VBATH is more negative than VBATL. With the positive and negative supply switches S2 and S1 in the positions shown, the line
driver amplifiers are powered between 0 V and VBATL. This mode minimizes the power consumption for short loop transmission. For long
loops, the driver voltage is increased by operating S1 to connect VBATH. To generate ringing, S2 is operated to apply VBATR, powering the
drivers from a total supply voltage of VBATR - VBATH. These conditions are shown in Figure 4.
SLIC
S2
0V
V
BATR
S1
LINE
V
BATL
V
BATH
LINE
DRIVERS
SUPPLY
SWITCHES
AI8XAF
Figure 3. SLIC with Voltage Supply Switching
V
BATR
V
SLICR
V
PKRING
/2
V
PKRING
/2
V
DCRING
V
PKRING
/2
0V
0V
V
BATR
- V
BATH
V
BATL
V
PKRING
/2
V
SLICH
V
BATH
SHORT LOOP
LONG LOOP
RINGING
AI8XAG
V
BATH
Figure 4. Driver Supply Voltage Levels
Conventional ringing is typically unbalanced ground or battery backed. To minimize the supply voltage required, most multi-rail SLICs use
balanced ringing as shown in Figure 4. The ringing has d.c., VDCRING, and a.c., VPKRING, components. A 70 V rms a.c. ring signal has a
peak value, VPKRING, of 99 V. If the d.c. component was 20 V, then the total voltage swing needed would be 99 + 20 = 119 V. There are
internal losses in the SLIC from the positive supply, VSLICR, and the negative supply, VSLICH. The sum of these two losses generally amounts
to a total of 10 V. This makes a total supply rail value of 119 + 10 = 129 V. In practice, the voltage might be distributed as VBATR = +60 V and
VBATH = -70 V. These values are nominal and some extra voltage should be provided to cover power supply voltage tolerance.
MAY 1998 - REVISED FEBRUARY 2005
Specifications are subject to change without notice.
Customers should verify actual device performance in their specific applications.
BOURNS [ BOURNS ELECTRONIC SOLUTIONS ]
