LUCL9215AAU-D AGERE [Agere Systems], LUCL9215AAU-D Datasheet - Page 24

• Manufacturer Part Number: LUCL9215AAU-D
• Description: Short-Loop Sine Wave Ringing SLIC
• Manufacturer: AGERE [Agere Systems]

Short-Loop Sine Wave Ringing SLIC
Applications
Power Control
Under normal device operating conditions, power dissi-
pation on the device must be controlled to prevent the
device temperature from rising above the thermal shut-
down and causing the device to shut down. Power dis-
sipation is highest with higher battery voltages, higher
current limit, and under shorter dc loop conditions.
Additionally, higher ambient temperature will also
reduce thermal margin.
To support required power ringing voltages, this device
is meant to operate with a high-voltage primary battery
(–65 V to –75 V typically). Thus, power control is nor-
mally achieved by use of the battery switch and an aux-
iliary lower absolute voltage battery. Operating
temperature range, maximum current limit, maximum
battery voltage, minimum dc loop length and protection
resistors values, airflow, and number of PC board lay-
ers will influence the overall thermal performance. The
following example illustrates typical thermal design
considerations.
The thermal resistance of the 32-pin PLCC package is
typically 50.5 C/W, which is representative of the natu-
ral airflow as seen in a typical switch cabinet with a
two-layer board.
The L9215 will enter thermal shutdown at a minimum
temperature of 150 C. The thermal design should
ensure that the SLIC does not reach this temperature
under normal operating conditions.
For this example, assume a maximum ambient operat-
ing temperature of 85 C, a maximum current limit of
30 mA, a maximum battery of –70 V, and an auxiliary
battery of –21 V. Assume a (worst-case) minimum dc
loop of 20
tors, and 200
the effects of parameter tolerance.
1. T
2. Allowed thermal rise = package thermal
24
impedance
65 °C = 50.5 °C/W
SLIC power dissipation (P
150 °C – 85 °C = 65 °C.
TSD
– T
AMBIENT(max)
of wire resistance, 30
•
for the handset. Additionally, include
SLIC power dissipation.
•
= allowed thermal rise.
SLIC power dissipation
D
) = 1.29 W.
protection resis-
Thus, if the total power dissipated in the SLIC is less
than 1.29 W, it will not enter the thermal shutdown
state. Total SLIC power is calculated as:
For the L9215, the worst-case SLIC on-hook active
power is 76.4 mW. Thus,
The power dissipated in the SLIC is the total power dis-
sipation less the power that is dissipated in the loop.
Thus, under the worst-case normal operating condi-
tions of this example, the thermal design, using the
auxiliary, is adequate to ensure the device is not driven
into thermal shutdown under worst-case operating con-
ditions.
dc Loop Current Limit
In the active modes, dc current limit is programmable
via an applied voltage source at the device’s V
control input. The voltage source may be an external
voltage source or derived via a resistor divider network
from the V
source. A programmable external voltage source may
be used to provide software control of the loop current
limit. The loop current limit (I
voltage at the onset of current limit by:
I
Note that there is a 12.5 k
istic in the current-limit region; thus, once in current
limit, the actual loop current will increase slightly, as
loop length decreases.
LIM
Total P
limit + SLIC quiescent power.
Total off-hook power = (I
tolerance)*(V
Total off-hook power = (0.030 A)(1.08) * (21) +
76.4 mW
Total off-hook power = 756.8 mW
SLIC P
Loop off-hook power = (I
min + 2R
Loop off-hook power = (0.030 A)(1.08)
60
Loop off-hook power = 293.9 mW
SLIC off-hook power = Total off-hook power – loop
off-hook power
SLIC off-hook power = 756.8 mW – 293.9 mW
SLIC off-hook power = 462.9 mW < 1.29 W
(mA) = 67 (mA/V) * V
+ 200
D
D
REF
= maximum battery
= total power – loop power
HANDSET
SLIC output or an external voltage
BATAPPLIED
)
)
PROG
) + SLIC on-hook power
LOOP
LOOP
LIM
slope to the I/V character-
(V)
) is related to the V
•
)(current-limit
maximum current
* 1.08)
September 2001
Agere Systems Inc.
2
2
•
(R
•
(20
LOOP(dc)
PROG
PROG
+