HC55121IBZ Intersil, HC55121IBZ Datasheet - Page 16

• Manufacturer Part Number: HC55121IBZ
• Manufacturer: Intersil

Specifications of HC55121IBZ

• Number Of Channels: 1
• On-hook Transmission: Yes
• Polarity Reversal: Yes
• On-chip Ring Relay Driver: Yes
• Longitudinal Balanced: 53
• Operating Supply Voltage (typ): 5V
• Operating Temp Range: -40C to 85C
• Loop Current Limit: 30mA
• Operating Temperature Classification: Industrial
• Pin Count: 28
• Mounting: Surface Mount
• Operating Current: 2.7mA
• Operating Supply Voltage (max): 5.25V
• Operating Supply Voltage (min): 4.75V
• Lead Free Status / RoHS Status: Compliant

Off Hook Overhead Voltage
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.
V
V
pm
OH off
OH(off) at Load
OH
sp(off)
pm(off)
OH(off) at Load
SAT
V
(
(R
= Pulse metering load impedance (typically 200Ω).
OH(off)
V
SAT
sense
SAT
DC FEED CURVE
) at Load
= Required (peak) off hook AC voltage for speech
s
V
Resistance Calculation
= Required (peak) off hook AC voltage for pulse
BH
+ 2R
resistance of the DC feed curve is used to
) = Required overhead for the DC voltage drop
I
LOOP CURRENT
LOOP(min)
INT
=
HC55120, HC55121, HC55130, HC55140, HC55142, HC55143, HC55150
=
2.5V
= Off hook overhead voltage at load
+ V
80
V
(reference Figure 17)
OH Rsense
OFF HOOK
OVER HEAD
×
pm off
sp(off)
I
LOOP max
(
P
(
), the required (peak) off hook
)
×
) and the required (peak) off hook
S
(
⎛
⎜
⎝
x Iloop
16
1
)
+
+
)
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
V
2R
----------------------------- -
pm(off)
+
sp off
V
P
(max)
Z
(
sp off
+
pm
(
2R
)
), if applicable.
+
SAT
)
)
S
OH
×
V
⎞
⎟
⎠
⎛
⎜
⎝
pm off
+
(off) at Load is
value for the off
1
2.0V
+
(
2R
----------------------------- -
)
S)
P
Z
, the
+
L
(EQ. 2)
(EQ. 3)
2R
S
BH
⎞
⎟
⎠
value of R
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 20.85kΩ (closest standard
value is 21kΩ).
The Switch Hook Detect threshold current is set by resistor
R
R
RDC_RAC = 50 x R
V
V
V
V
R
OH(on) AT LOAD
OH(off) AT LOAD
SAT(off)
OH on
OH on
OH on
D
SAT on
V
V
and is calculated using Equation 7. For the above
OH(on)
V
V
OH(off)
(
(
(
SAT
SAT
(
DC FEED CURVE
V
)
)
)
V
BH
BH
=
)
=
=
=
DC FEED CURVE
SAT(off)
=
V
--------------------------------------- -
(
7.2mA
3.0V
ISH-
OH(off) at Load
LOOP CURRENT
ISH-(min)
----------------- -
7.2mA
I
I
LOOP CURRENT
2.85V
LOOP(min)
LOOP(min)
2.5V
I
ISH-
2.5V
LOOP(min)
) R
is equal to 417Ω as calculated in Equation 4.
(min)
(
×
SAT(on)
SAT
SAT
R
SAT(off)
417Ω
SAT off
=
R
SAT
SAT
R
R
395Ω
SAT
SAT
value, to calculate the RDC_RAC
(
SAT
=
value to determine the RDC_RAC
)
value.
)
8.34V
--------------- -
20mA
would equal 417Ω and
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
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
sp(off)
spm(off)
OH(off) at Load
SAT
SAT
OH(off) at Load
=
(min)
(R
417Ω
.
= 3.2V
SAT(off)
sp(on)
= 0V
(Equation 4).
PEAK
PEAK
= 0.775V
), is given in
= 8.34V the
SAT
divided by
,
,
June 1, 2006
is equal
FN4659.13
(EQ. 4)
(EQ. 6)
(EQ. 5)
RMS