HC55120CM INTERSIL [Intersil Corporation], HC55120CM Datasheet - Page 14

• Manufacturer Part Number: HC55120CM
• Description: Low Power Universal SLIC Family
• Manufacturer: INTERSIL [Intersil Corporation]

†
On Hook Overhead Voltage
Switch Hook Detect threshold (I
current for a constant on hook overhead voltage is defined
as ISH-.
The on hook overhead voltage, required for a given signal
level at the load, must take into account the AC voltage drop
across the 2 external protection resistors (R
internal sense resistors (R
on hook overload voltage is calculated using Equation 1.
where
V
V
R
R
Z
1.5V = Additional on hook overhead voltage requirement
HC55120, HC55121, HC55130, HC55131, HC55140, HC55141, HC55142, HC55143, HC55150, HC55151
V
Internal overhead voltage automatically generated by the SLIC.
OH(on) at Load
L
OH on at Load
sp(on)
P
S
ISH- = I
= AC load impedance for (600 )
= Protection Resistors (Typically 30 )
= Internal Sense Resistors (40 )
V
OH(on)
V
SHD
= Required on hook transmission for speech
BH
DC FEED CURVE
(0.6)
ISH-
LOOP CURRENT
2.5V
VBH
2.5V
=
= On hook overhead voltage at load
ON HOOK
OVERHEAD
†
I
V
SHD
sp on
S
4-14
VOH(on) AT LOAD
) as shown in Figure 16. The AC
1
+
The on hook overhead voltage
at the load (V
is independent of the V
battery voltage. Once set, the
on hook voltage remains
constant as the V
voltage changes. The on hook
voltage also remains constant
over temperature and line
leakages up to 0.6 times the
2R
----------------------------- -
SLIC SELF PROGRAMMING
SHD
P
Z
+
). The maximum loop
L
2R
ISH-
S
+
OH
P
1.5V
) and the 2
FIGURE 15. UniSLIC14 DC FEED CURVE
(on) at Load)
I
SHD
BH
IOH
battery
BH
(EQ. 1)
R
SAT
ILOOP(min)
LOOP CURRENT (mA)
To account for any process and temperature variations in the
performance of the SLIC, 1.5V is added to the overhead
voltage requirement for the on hook case in Equation 1 and
2.0V for the off hook case in Equation 3. Note the 2.5V
overhead is automatically generated in the SLIC and is not
part of the external overhead programming.
Off Hook Overhead Voltage
FIGURE 16. OVERHEAD VOLTAGE OF THE TIP AND RING
V
V
ZL
OH(off)
(LOAD)
V
VOH(off) AT LOAD
EXTERNAL PROTECTION
RESISTOR
SAT
DC FEED CURVE
V
Z
BH
L
AMPLIFIERS
I
LOOP CURRENT
LOOP(min)
2.5V
2R
OFF HOOK
OVER HEAD
P
V
Where:
V
transmission delivered to the load.
ZL
OH ON OFF
is the required on hook or offhook
2R
INTERNAL SENSE
RESISTORS
S
The off hook overhead
voltage V
also independent of the V
battery voltage and remains
constant over temperature.
The required off hook
overhead voltage is the sum
of the AC and DC voltage
drops across the internal
sense resistors (R
REQUIRED
OVERHEAD VOLTAGE
V
=
ILOOP(max)
OH
2R
----------------------------- - V
(ON, OFF)
OH
UniSLIC14
P
Z
CONSTANT
CURRENT
REGION
+
(off) at Load is
L
60k SLOPE
2R
TIP AND RING
AMPLIFIERS
S
S)
ZL
, the
BH