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參數(shù)資料
| 型號： | HC5549IM |
| 廠商： | HARRIS SEMICONDUCTOR |
| 元件分類： | 模擬傳輸電路 |
| 英文描述： | THERMISTOR PTC1KOHM 70 DEG 0805 |
| 中文描述： | TELECOM-SLIC, PQCC28 |
| 文件頁數(shù)： | 5/13頁 |
| 文件大小： | 87K |
| 代理商： | HC5549IM |
4-84
Design Equations
Loop Supervision Thresholds
SWITCH HOOK DETECT
The switch hook detect threshold is set by a single external
resistor, R
SH
. Equation 1 is used to calculate the value of R
SH
.
The term I
SH
is the desired DC loop current threshold. The
loop current threshold programming range is from 5mA to
15mA.
GROUND KEY DETECT
The ground key detector senses a DC current imbalance
between the Tip and Ring terminals when the ring terminal is
connected to ground. The ground key detect threshold is not
externally programmable and is internally fixed to 12mA
regardless of the switch hook threshold.
RING TRIP DETECT
The ring trip detect threshold is set by a single external
resistor, R
RT
. I
RT
should be set between the peak ringing
current and the peak off hook current while still ringing.
The capacitor C
RT
, in parallel with R
RT
, will set the ring trip
response time.
Loop Current Limit
The loop current limit of the device is programmed by the
external resistor R
IL
. The value of R
IL
can be calculated
using Equation 3.
LIM
The term I
LIM
is the desired loop current limit. The loop
current limit programming range is from 15mA to 45mA.
Impedance Matching
The impedance of the device is programmed with the
external component R
S
. R
S
is the gain setting resistor for
the feedback amplifier that provides impedance matching. If
complex impedance matching is required, then a complex
network can be substituted for R
S
.
RESISTIVE IMPEDANCE SYNTHESIS
The source impedance of the device, Z
O
, can be calculated
in Equation 4.
The required impedance is defined by the terminating
impedance and protection resistors as shown in Equation 5.
4-WIRE TO 2-WIRE GAIN
The 4-wire to 2-wire gain is defined as the receive gain. It is
a function of the terminating impedance, synthesized
impedance and protection resistors. Equation 6 calculates
the receive gain, G
42
.
When the device source impedance and protection resistors
equals the terminating impedance, the receive gain equals
unity.
2-WIRE TO 4-WIRE GAIN
The 2-wire to 4-wire gain (G
24
) is the gain from tip and ring to
the VTX output. The transmit gain is calculated in Equation 7.
When the protection resistors are set to zero, the transmit
gain is -6dB.
TRANSHYBRID GAIN
The transhybrid gain is defined as the 4-wire to 4-wire gain
(G
44
).
When the protection resistors are set to zero, the transhybrid
gain is -6dB.
COMPLEX IMPEDANCE SYNTHESIS
Substituting the impedance programming resistor, R
S
, with a
complex programming network provides complex
impedance synthesis.
The reference designators in the programming network
match the evaluation board. The component R
S
has a
different design equation than the R
S
used for resistive
impedance synthesis. The design equations for each
component are provided below.
R
SH
600 I
SH
=
(EQ. 1)
R
RT
1800 I
RT
=
(EQ. 2)
R
IL
------------
=
(EQ. 3)
R
S
400 Z
O
)
=
(EQ. 4)
Z
O
Z
L
2R
P
–
=
(EQ. 5)
G
42
2
Z
O
P
L
-----------------------------------------
–
=
(EQ. 6)
G
24
Z
O
P
L
-----------------------------------------
–
=
(EQ. 7)
G
44
Z
P
O
L
+
--------+
–
=
(EQ. 8)
FIGURE 1. COMPLEX PROGRAMMING NETWORK
2-WIRE
NETWORK
C
2
R
1
R
2
PROGRAMMING
NETWORK
C
P
R
S
R
P
R
S
400
R
1
2 R
P
)
–
(
)
×
=
(EQ. 9)
R
P
400
R
2
×
=
(EQ. 10)
C
P
C
2
400
=
(EQ. 11)
HC5549
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