HC55121IM Intersil, HC55121IM Datasheet - Page 19

• Manufacturer Part Number: HC55121IM
• Manufacturer: Intersil

Specifications of HC55121IM

• 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
• Package Type: PLCC
• 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: Not Compliant

Substituting Equation 21 for V
simplifying results in Equation 31.
(AC) 2-Wire Impedance
The AC 2-wire impedance (Z
into the SLIC, including the fuse resistors. The formula to
calculate the proper Z
shown in Equation 32.
Equation 32 can now be used to match the SLIC’s
impedance to any known line impedance (Z
EXAMPLE:
Calculate Z
R
Z
Note: Some impedance models, with a series capacitor, will
cause the op-amp feedback to behave as an open circuit
DC. A resistor with a value of about 10 times the reactance
of the Z
frequency of interest (200Hz for example) can be placed in
parallel with the capacitor in order to solve the problem
(736kΩ for a 10.8nF capacitor).
Calculating Tip and Ring Voltages
The on hook tip to ground voltage is calculated using
Equation 34. The minus 1.0 volt results from the SLIC self
programming. ISH- is the maximum loop current for a
constant on hook overhead voltage (ISH- = I
the value of R
On hook Tip Voltage
The off hook tip to ground voltage is calculated using
Equation 35. I
allowed by the design and the value of R
calculated in Equation 4.
Off hook Tip Voltage
The on hook ring to ground voltage is calculated using
Equation 36. The 1.5 volt results from the SLIC self
programming. ISH- is the maximum loop current for a
G
Z
V
V
T
T
P
4 4
TIP onhook
Z
TIP offhook
–
= 108kΩ in series with 0.0108µF.
–
T
=
= 30Ω.
I
LOOP MAX
(
(
=
200
=
T
200 600
-----------
V
V
capacitor (2.16µF/200 = 10.8nF) at the low
•
RX
TX
(
(
⎛
⎜
⎝
T
Z
)
)
TR
to make Z
=
SAT(off)
=
LOOP(min)
=
HC55120, HC55121, HC55130, HC55140, HC55142, HC55143, HC55150
)
–
+
–
–
–
×
2
2R
---------------------------------- -
jω2.16X10
1.0V
1V
R
⎛
⎜
⎝
Z
----------------------- -
Z
P
P
L
L
–
T
+ 2R
)
is calculated in Equation 4.
+
+
(
1
for matching the 2-wire impedance is
TR
I
Z
–
LOOP min
is the minimum loop current
TR
(
P
ISH-
= 600Ω in series with 2.16µF.
⎞
⎟
⎠
–
6
19
TR
(
TR
–
)
) is the impedance looking
2 ( ) 30
⎛
⎝
R
--------------------- -
in Equation 30 and
)
)
SAToff
(
R
--------------------------
2
SAT off
)
⎞
⎟
⎠
2
(
⎞
⎠
SAT(off)
)
TR
SHD
).
(0.6)) and
is
(EQ. 32)
(EQ. 31)
(EQ. 33)
(EQ. 34)
(EQ. 35)
constant on hook overhead voltage (ISH- = I
the value of R
On hook Ring Voltage
The calculation of the ring voltage with respect to ground in
the off hook condition is dependent upon whether the SLIC
is in current limit or not.
The off hook ring to ground voltage (in current limit) is
calculated using Equation 37. I
current limit and R
The minus 0.2V is a correction factor for the 60kΩ slope in
Figure 15.
Off hook Ring Voltage in Current Limit
The off hook ring to ground voltage (not in current limit) is
calculated using Equation 38. The 1.5V results from the
SLIC self programming. I
current allowed by the design and the value of R
calculated in Equation 4.
Off hook Ring Voltage not in Current Limit
Layout Considerations
Systems with Dual Supplies (V
If the V
recommended that an additional diode be placed in series
with the V
on pin 8 of the device and cathode to the external supply.
This external diode will inhibit large currents and potential
damage to the SLIC, in the event the V
to GND. If V
required. Suggested (not required) supply sequence V
V
Floating the PTG Pin
The PTG pin is a high impedance pin (500kΩ) that is used to
program the 2-wire to 4-wire gain to either 0dB or -6dB.
If 0dB is required, it is necessary to float the PTG pin. The
PC board interconnect should be as short as possible to
minimize stray capacitance on this pin. Stray capacitance on
this pin forms a low pass filter and will cause the 2-wire to
4-wire gain to roll off at the higher frequencies.
If a 2-wire to 4-wire gain of -6dB is required, the PTG pin
should be grounded as close to the device as possible.
V
V
V
–
RING CL
RING NCL
BL
RING onhook
I
LOOP MIN
- V
(
(
CC
BL
(
(
)
.
BH
supply is not derived from the V
)
=
BL
=
)
V
supply. The orientation of this diode is anode
×
SAT(off)
)
TIP offhook
V
R
is derived from V
=
BH
P
L
(
V
+
BH
is the load resistance across tip and ring.
1.5V
is calculated in Equation 4.
+
1.5V
LOOP(min)
)
+
–
(
I
I
LOOP MAX
LOOP min
+
(
LIM
ISH
BH
(
(
is the programmed loop
then this diode is not
is the minimum loop
)
BH
⎛
⎝
)
R
--------------------------
)
)
BH
R
⎛
⎝
SAT off
and V
R
--------------------------
L
SAT off
2
BH
supply is shorted
–
(
SHD
0.2V
2
supply, it is
(
)
⎞
⎠
BL
SAT(off)
(0.6)) and
)
⎞
⎠
)
June 1, 2006
(EQ. 36)
FN4659.13
(EQ. 37)
(EQ. 38)
BH
is
-