
26
FN4659.13
June 1, 2006
Given: VBH = VBL = -48V, Loop current = 30mA, RL (load
across tip and ring) = 600
, Quiescent battery power =
(48V) (0.8mA) = 38.4mW, Quiescent VCC power = (5V)
(2.7mA) = 13.5mW, Power sharing resistor = 600
.
1. Without power sharing, the on-chip power dissipation
would be 952mW (Equation 42).
2. With power sharing, the on-chip power dissipation is
412mW (Equation 43). A power redistribution of 540mW.
On-chip power dissipation without power sharing resistor.
On-chip power dissipation with 600
power sharing resistor.
Battery Selection
Battery selection is a technique, for a two battery supply
system, where the SLIC automatically diverts the loop
current to the most appropriate supply for a given loop
length. This results in significant power savings and lowers
the total power consumption on short loops. This technique
is particularly useful if most of the lines are short, and the on
hook condition requires a -48V battery. In Figure 26, it can
be seen that for long loops the majority of the current comes
from the high battery supply (VBH) and for short loops from
the low battery supply (VBL).
PD
V
BH
() 30mA
() 38.4mW 13.5mW
RL
() 30mA
()
2
–
++
=
(EQ. 42)
PD
952mW
=
PD
V
BH
() 30mA
() 38.4mW 13.5mW
++
=
(EQ. 43)
R
L
() 30mA
()
2
–
R
PS
() 30mA
()
2
–
PD
412mW
=
FIGURE 25. POWER SHARING (SINGLE SUPPLY SYSTEMS)
VTX
VRX
UniSLIC14
TIP
RING
VBL
VBH
-48V
ON SHORT LOOPS, THE
MAJORITY OF CURRENT
FLOWS OUT THE VBL PIN
RPS
FIGURE 26. BATTERY SELECTION (DUAL SUPPLY SYSTEMS)
LOOP
CUR
RE
NT
(mA)
0
35
30
25
20
15
10
5
1000
900
800
600
700
575
550
525
500
475
450
400
350
300
250
200
150
2000
LOOP RESISTANCE (
)
100
40
VBH = -48V
VBL = -24V
RILim = 33.2k
VBL
VBH
VBL
Pinouts - 28 Lead PLCC Packages
HC55120
(28 LEAD PLCC)
TOP VIEW
HC55121
(28 LEAD PLCC)
TOP VIEW
DR
C3
C2
C1
SH
D
CDC
DT
RRLY
PT
G
VT
X
NC
VR
X
ZT
CH
RSYNC
ILIM
ROH
RD
AGND
GKD
VCC
1
2
3
4
5
6
7
8
9
10
11
12 13 14 15 16 17 18
19
20
21
22
23
24
25
26
27
28
BGND
TIP
VBH
VBL
RING
CRT
RDC_RAC
DR
C3
C2
C1
SH
D
CDC
DT
RRLY
PT
G
VT
X
SP
M
VR
X
ZT
CH
RSYNC_REV
ILIM
ROH
RD
AGND
GKD
VCC
1
2
3
4
5
6
7
8
9
10
11
12 13 14 15 16 17 18
19
20
21
22
23
24
25
26
27
28
BGND
TIP
VBH
VBL
RING
CRT_REV
RDC_RAC
HC55120, HC55121, HC55130, HC55140, HC55142, HC55143, HC55150