66
Functional Diagram
The truth table for the internal logic of the HC55171 is pro-
vided in the above table. This family of ringing SLICS can be
configured to support traditional unbalanced ringing and thru
SLIC balanced ringing. Refer to the HC5509A1R3060 for
unbalanced ringing application information. The device oper-
ating states used by thru SLIC ringing applications are loop
power denial and normal feed. During loop power denial, the
tip and ring amplifiers are disabled (high impedance) and the
DC voltage of each amplifier approaches ground. The SLIC
will not provide current to the subscriber loop during this mode
and will not detect loop closure. Voice transmission occurs
during the normal loop feed mode. During normal loop feed
the SLIC is completely operational and performs all transmis-
sion and supervisory functions.
Power Dissipation
Careful thermal design is required to guarantee that the
maximum junction temperature of 150
o
C of the device is not
exceeded. The junction temperature of the SLIC can be cal-
culated using:
Where T
A
is maximum ambient temperature and
θ
JA
is junc-
tion to air thermal resistance (and is package dependent).
The entire term in parentheses yields the SLIC power dissi-
pation. The power dissipation of the subscriber loop does
not contribute to device junction temperature and is sub-
tracted from the power dissipation term. Operating at 85
o
C,
the maximum PLCC SLIC power dissipation is 1.18W. Like-
wise, the maximum SOIC SLIC power dissipation is 0.92W.
R
R
V
REF
R
V
RX
OUT 1
R/20
R/2
TIP
TA
R
2R
2R
R
90K
RING
SENSE 1
RA
4.5K
25K
25K
100K
100K
4.5K
90K
RF
25
17
12
+2V
TF
14
RF
15
16
26
3
OP AMP
V
RING
V
TX
GM
28
11
RF2
BIAS
NETWORK
AGND
V
CC
I
TSD
GK
RFC
SH
F0
F1
RS
ALM
RTD
SHD
TST
V
BAT
-IN 1
13
24
19
2
1
TF
BGND
22
27
4
5
6
9
20
21
7
8
10
R = 108k
R
R
100K
100K
90K
18
RTI
NU
I
LMT
SENSE
RING
SENSE 2
RDI
RDO
+
-
+
-
THERM
LTD
SHD
RTD
FAULT
DET
+
-
REF
VB/2
+
-
+
-
+
-
HC55171 DEVICE TRUTH TABLE
F1
F0
STATE
0
0
Loop power Denial Active
0
1
Power Down Latch RESET, Power on
RESET
1
0
RD Active
1
1
Normal Loop feed
T
J
T
A
θ
JA
I
CC
V
CC
I
BAT
V
BAT
I
LOOP
(
)
2
R
LOOP
(
)
–
+
(
)
+
=
(EQ. 1)
HC55171