参数资料
型号: ISL5585GCM
厂商: INTERSIL CORP
元件分类: 模拟传输电路
英文描述: CONNECTOR ACCESSORY
中文描述: TELECOM-SLIC, PQCC28
封装: PLASTIC, MS-018AB, LCC-28
文件页数: 15/22页
文件大小: 425K
代理商: ISL5585GCM
15
Most applications do not specify charging current
requirements during standby. When specified, the typical
charging current may be as high as 5mA
.
Forward Active
Overview
The forward active mode (FA, 001) is the primary AC
transmission mode of the device. On hook transmission, DC
loop feed and voice transmission are supported during forward
active. Loop supervision is provided by either the switch hook
detector (E0 = 1) or the ground key detector (E0 = 0). The
device may be operated from either high or low battery for on-
hook transmission and low battery for loop feed.
On-Hook Transmission
The primary purpose of on hook transmission will be to
support caller ID and other advanced signalling features.
The transmission over load level while on hook is 1 V
PEAK
.
When operating from the high battery, the DC voltages at Tip
and Ring are MTU compliant. The typical Tip voltage is -4V
and the Ring voltage is a function of the battery voltage for
battery voltages less than -60V as shown in Equation 48.
Loop supervision is provided by the switch hook detector at
the DET output. When DET goes low, the low battery should
be selected for DC loop feed and voice transmission.
Feed Architecture
The design implements a voltage feed current sense
architecture. The device controls the voltage across Tip and
Ring based on the sensing of load current.Internal resistors
(R
CS
) are placed in series with Tip and Ring outputs to
provide the current sensing. The diagram below illustrates
the concept.
By monitoring the current at the amplifier output, a negative
feedback mechanism sets the output voltage for a defined
load. The amplifier gains are set by resistor ratios (R
A
, R
B
,
R
C
) providing all the performance benefits of matched
resistors. The internal sense resistor, R
CS
, is much smaller
than the gain resistors and is typically 20
for this device.
The feedback mechanism, K
S
, represents the amplifier
configuration providing the negative feedback.
Transhybrid Balance
The final step in completing the impedance synthesis design
is calculating the necessary gains for transhybrid balance.
The AC feed back loop produces an echo at the V
TX
output
of the signal injected at V
IN
. The echo must be cancelled to
maintain voice quality. Most applications will use a summing
amplifier in the CODEC front end as shown in Figure 10 to
cancel the echo signal.
The resistor ratio, R
F
/R
A
, provides the final adjustment for
the transmit gain, G
TX
(V
2w
to PCM, Figure 18). The transmit
gain is calculated using Equation 49.
R
F
R
A
Most applications set R
F
= R
A
, hence the device 2-wire to
4-wire equals the transmit gain. Typically R
A
is greater than
20k
to prevent loading of the device transmit output. The
value of the RF resistor should greater than the minimum
load spec of the CODEC’s internal amplifier (typical value
30.1k
).
The resistor ratio, R
F
/R
B
, is determined by the transhybrid
gain of the device, G
44
. R
F
is previously defined by the
transmit gain requirement and R
B
is calculated using
Equation 50.
Power Dissipation
The power dissipated by the device during on hook
transmission is strictly a function of the quiescent currents
for each supply voltage during Forward Active operation.
Off hook power dissipation is increased above the quiescent
power dissipation by the DC load. If the loop length is less
than or equal to R
KNEE
, the device is providing constant
current, I
A
, and the power dissipation is calculated using
Equation 52.
V
RING
V
BH
5
+
=
(EQ. 48)
FIGURE 9. VOLTAGE FEED CURRENT SENSE DIAGRAM
+
-
+
-
V
IN
V
OUT
R
C
R
CS
R
L
R
B
R
A
K
S
FIGURE 10. TRANSHYBRID BALANCE INTERFACE
+
-
R
F
R
A
R
B
ISL5585
CODEC
+2.4V
RX OUT
TX IN
-IN
AUX
VTX
R
R
+-
1:1
R
S
T
A
R
IN
G
TX
G
24
-------
Z
O
2R
P
L
Z
O
+
)
-----------+
R
F
R
A
-------
=
=
(EQ. 49)
R
B
R
A
44
----------
=
R
A
R
S
---------
Z
--------------------------------------
2R
O
Z
O
+
+
=
(EQ. 50)
P
FAQ
V
BH
I
×
BHQ
V
BL
I
BLQ
×
V
CC
I
CCQ
×
+
+
=
(EQ. 51)
P
FA IA
(
)
P
FA Q
(
)
V
BL
xI
A
(
)
R
LOOP
xI
2A
(
)
+
=
(EQ. 52)
ISL5585
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