HC55120CM INTERSIL [Intersil Corporation], HC55120CM Datasheet - Page 15

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

protection resistors (R
voltage for speech (V
voltage for the pulse metering (V
The off hook overhead voltage is defined in Equation 2 and
calculated using Equation 3.
where:
V
V
across sense resistors (2R
V
V
metering
where:
80 = 2R
Z
2.0V = Additional off hook overhead voltage requirement
R
The R
determine the value of the RDC_RAC resistor (Equation 6).
The value of this resistor has an effect on both the on hook
and off hook overheads. In most applications the off hook
condition will dominate the overhead requirements.
Therefore, we’ll start by calculating the R
hook conditions and then verify that the on hook conditions
are also satisfied.
value of R
HC55120, HC55121, HC55130, HC55131, HC55140, HC55141, HC55142, HC55143, HC55150, HC55151
V
V
R
V
OH(off) at Load
OH
pm
OH(off) AT LOAD
OH off at Load
sp(off)
pm(off)
OH(off) at Load
SAT(off)
SAT
V
V
OH(off)
(R
= Pulse metering load impedance (typically 200 ).
SAT
SAT
sense
V
= Required (peak) off hook AC voltage for speech
s
Resistance Calculation
= Required (peak) off hook AC voltage for pulse
BH
=
DC FEED CURVE
+ 2R
SAT(off)
resistance of the DC feed curve is used to
V
--------------------------------------- -
OH(off) at Load
) = Required overhead for the DC voltage drop
I
I
LOOP CURRENT
LOOP(min)
LOOP(min)
2.5V
I
INT
LOOP(min)
=
=
= Off hook overhead voltage at load
+ V
80 I
is equal to 417 as calculated in Equation 4.
V
(reference Figure 17)
OH Rsense
pm off
R
sp(off)
SAT
R
LOOP max
P
SAT
), the required (peak) off hook
=
4-15
) and the required (peak) off hook
S
--------------- -
20mA
8.34V
x Iloop
1
When considering the Off
hook condition, R
to V
Iloop
For the given system
requirements (recommended
application circuit in back of
data sheet): Iloop (min) =
20mA, Iloop (max) = 30mA,
V
V
V
+
+
OH(off) at Load
sp(off)
spm(off)
V
2R
----------------------------- -
pm(off)
+
OH(off) at Load
sp off
=
V
(min)
P
(max)
Z
sp off
417
+
pm
= 3.2V
2R
), if applicable.
= 0V
(Equation 4).
+
SAT
)
S
V
pm off
+
PEAK
PEAK
1
value for the off
2.0V
= 8.34V the
+
SAT
2R
----------------------------- -
divided by
,
,
P
is equal
Z
+
L
(EQ. 4)
(EQ. 2)
(EQ. 3)
2R
S
Before using this R
resistor, we need to verify that the on hook requirements will
also be met.
V
met if we use the R
If the on hook overhead requirement is not met, then we
need to use the R
resistor value. The external saturation guard resistor
RDC_RAC is equal to 50 times R
In the example above R
RDC_RAC would then equal to 20.85k (closest standard
value is 21k ).
The Switch Hook Detect threshold current is set by resistor
R
example R
next closest standard value is 41.2k
The true value of ISH-, for the selected value of R
by Equation 8:
For the example above, ISH- equals 7.28mA (500 x 0.6/ 41.2K).
Verify that the value of ISH- is above the suspected line
leakage of the application. The UniSLIC family will provide a
constant on hook voltage level for leakage currents up to this
value of line leakage.
RDC_RAC = 50 x R
R
V
V
V
ISH- =
R
OH(on) AT LOAD
OH on
OH on
OH on
D
D
SAT on
V
OH(on)
and is calculated using Equation 7. For the above
=
V
SAT
------------
I
DC FEED CURVE
500
SHD
500
--------- - (0.6)
R
V
BH
D
=
=
=
=
D
7.2mA 417
3.0V
ISH- R
LOOP CURRENT
ISH-(min)
----------------- -
7.2mA
is calculated to be 41.6k (500/12mA). The
2.85V
2.5V
ISH-
(min)
SAT(on)
SAT
SAT
R
SAT(off)
=
SAT off
SAT
R
395
SAT
value, to calculate the RDC_RAC
SAT
value to determine the RDC_RAC
value.
would equal 417 and
The on hook overhead voltage
calculated with the off hook
R
Equation 5 and equals 3.0V.
The on hook overhead
calculated with Equation 1
equals 2.85V for the given
system requirements
(recommended application
circuit in back of data sheet):
Switch Hook Detect threshold
= 12mA, ISH- = (0.6)12mA =
7.2mA, V
Thus, the on hook overhead
requirements of 2.85V will be
SAT
SAT
(R
.
SAT(off)
sp(on)
= 0.775V
), is given in
D
is given
(EQ. 7)
(EQ. 8)
(EQ. 6)
(EQ. 5)
RMS