Preliminary Data Sheet
September 2001
High-Voltage Ringing SLIC for VoIP Applications
L9500A
22
Agere Systems Inc.
Applications
(continued)
dc Loop Current Limit
Current limit may be chosen from two discrete values,
25 mA or 40 mA, depending on if V
PROG
is grounded
(25 mA) or left floating (40 mA). Note that there is a
12.5 k
slope to the I/V characteristic in the current-
limit region; thus, once in current limit, the actual loop
current will increase slightly, as loop length decreases.
The above describes the active mode steady-state cur-
rent-limit response. There will be a transient response
of the current-limit circuit upon an on- to off-hook transi-
tion. Typical active mode transient current-limit
response is given in Table 19.
Table 19. Typical Active Mode On- to Off-Hook Tip/
Ring Current-Limit Transient Response
Overhead Voltage
Active Mode
Overhead is fixed to a nominal 7.0 V, which is adequate
for an on-hook transmission of 3.14 dBm into 900
with additional head room for a 500 mV PPM signal.
Scan Mode
If the magnitude of the primary battery is greater than
51 V, the magnitude of the open loop tip-to-ring open
loop voltage is clamped typically between 44 V and
51 V. If the magnitude of the primary battery is less
than a nominal 51 V, the overhead voltage will track the
magnitude of the battery voltage, i.e., the magnitude of
the open circuit tip-to-ring voltage will be 4 V to 6 V less
than battery. In the scan mode, overhead is unaffected
by V
OVH
.
On-Hook Transmission Mode
If the magnitude of the primary battery is greater than
51 V, the magnitude of the open loop tip-to-ring open
loop voltage is clamped typically between 41 V and
49 V. If the magnitude of the primary battery is less
than a nominal 51 V, the overhead voltage will track the
magnitude of the battery voltage, i.e., the magnitude of
the open circuit tip-to-ring voltage will be 6 V to 8 V less
than battery. In the scan mode, overhead is unaffected
by V
OVH
.
Ring Mode
In the ring mode, to maximize ringing loop length, the
overhead is decreased to the saturation of the tip ring
drive amplifiers, a nominal 4 V. The tip to ground volt-
age is 1 V, and the ring to V
BAT1
voltage is 3 V. In the
ring mode, overhead is unaffected by V
OVH
.
During the ring mode, to conserve power, the receive
input at RCVN/RCVP is deactivated. During the ring
mode, to conserve power, the ACC amplifier in the
transmit direction at VITR is deactivated. However, the
AX amplifier at VTX is active during the ring mode; dif-
ferential ring current may be sensed at VTX during the
ring mode.
Loop Range
The dc loop range is calculated using:
R
L
=
– 2R
P
– R
DC
V
BAT2
is typically applied under off-hook conditions for
power conservation and SLIC thermal considerations.
The L9500 is intended for short-loop applications and,
therefore, will always be in current limit during off-hook
conditions. However, note that the ringing loop length
rather than the dc loop length will be the factor to deter-
mine operating loop length.
Parameter
Value
I
LIM
+ 60
Unit
mA
dc Loop Current:
Active Mode
R
LOOP
= 100
On- to Off-hook
Transition t < 5 ms
dc Loop Current:
Active Mode
R
LOOP
= 100
On- to Off-hook
Transition t < 50 ms
dc Loop Current:
Active Mode
R
LOOP
= 100
On- to Off-hook
Transition t < 300 ms
I
LIM
+ 20
mA
I
LIM
mA
BAT2
V
V
OH
–
I
LIMIT