HC55120_06 Datasheet, PDF (26/36 Pages) Intersil Corporation – Low Power Universal SLIC Family

HC55120, HC55121, HC55130, HC55140, HC55142, HC55143, HC55150
Given: V_BH = V_BL = -48V, Loop current = 30mA, R_L (load
across tip and ring) = 600Ω, Quiescent battery power =
(48V) (0.8mA) = 38.4mW, Quiescent VCC power = (5V)
(2.7mA) = 13.5mW, Power sharing resistor = 600Ω.
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.
PD = (V_BH)(30mA) + 38.4mW + 13.5mW – (RL)(30mA)²
PD = 952mW
(EQ. 42)
On-chip power dissipation with 600Ω power sharing resistor.
PD = (V_BH)(30mA) + 38.4mW + 13.5mW
– (R_L)(30mA)² – (R_PS)(30mA)²
PD = 412mW
(EQ. 43)
TIP ^UniSLIC14
V_TX
RING
ON SHORT LOOPS, THE
MAJORITY OF CURRENT
FLOWS OUT THE V_BL PIN
V_RX
V_BL
R_PS
V_BH
-48V -48V
FIGURE 25. POWER SHARING (SINGLE SUPPLY SYSTEMS)
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 (V_BH) and for short loops from
the low battery supply (V_BL).
40
35
V_BH
V_BL
30
25
VBH = -48V
20
VBL = -24V
RILim = 33.2kΩ
15
10
5 V_BL
0
V_BH
LOOP RESISTANCE (Ω)
FIGURE 26. BATTERY SELECTION (DUAL SUPPLY SYSTEMS)
Pinouts - 28 Lead PLCC Packages
HC55120
(28 LEAD PLCC)
TOP VIEW
HC55121
(28 LEAD PLCC)
TOP VIEW
4 3 2 1 28 27 26
RING 5
BGND 6
TIP 7
VBH 8
VBL 9
RDC_RAC 10
CRT 11
25 ^AGND
24 ^RSYNC
23 ^ILIM
22 ^ROH
21 ^RD
20 ^VCC
19 GKD
12 13 14 15 16 17 18
4 3 2 1 28 27 26
RING 5
BGND 6
TIP 7
VBH 8
VBL 9
RDC_RAC 10
CRT_REV 11
25 AGND
24 RSYNC_REV
23 ILIM
22 ROH
21 RD
20 ^VCC
19 GKD
12 13 14 15 16 17 18
26
FN4659.13
June 1, 2006