ISL5586FCM Intersil, ISL5586FCM Datasheet - Page 10

• Manufacturer Part Number: ISL5586FCM
• Description: Ringing Subscriber Interface
• Manufacturer: Intersil

Specifications of ISL5586FCM

• Package / Case: 28-PLCC

The slope of the feed characteristic and the battery voltage
define the maximum loop current on the shortest possible
loop as the short circuit current I
The term I
line segment I
loop current limit function.
The maximum loop resistance for a programmed loop
current is defined as R
When R
constant current feed to constant voltage, resistive feed. The
line segment I
load characteristic.
Power Dissipation
The power dissipated by the SLIC in the Forward Active
mode while on hook is strictly a function of the quiescent
currents for each supply.
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
current (I
Equation 26.
If the loop length is greater than R
operating in the constant voltage, resistive feed region. The
power dissipated in this region is calculated using Equation 27.
I
I
R
I
P
P
P
SC
A
B
FIGURE 6. I
FAQ
FA IA
FA IB
KNEE
=
=
(
(
I
=
LIM
V
----------------------- -
=
R
I
TR OC
)
)
LIM
LOOP
=
KNEE
V
=
=
+
A)
(
BH
P
LIM
V
----------------------- -
V
--------------------------------------------------------------
P
+
, and the power dissipation is calculated using
FA Q
TR OC
TR OC
FA Q
I
×
V
----------------------------------------------------- -
LOOP
LIM
)
I
is the programmed current limit, 1760/R
A
( )
B
SC
TR OC
I
(
is exceeded, the device will transition from
(
( )
BHQ
I
represents the constant current region of the
LIM
represents the resistive feed portion of the
(
+
KNEE
+
)
)
1.1e4
VERSUS R
2R
(
1.1e4
–
+
(
V
)
V
R
P
V
BL
–
BL
LOOP
BL
KNEE
2R
xI
, the device is providing constant
xI
R
×
B
LOOP
P
A
)
I
I
BLQ
)
LIM
I
–
LIM
.
–
10
LOOP
(
R
(
(Ω)
R
LOOP
+
SC
LOOP
V
KNEE
LOAD CHARACTERISTIC
CC
.
I
xI
A
xI
×
R
2
I
KNEE
2
, the device is
B
CCQ
A
)
)
I
B
(EQ. 21)
(EQ. 22)
(EQ. 23)
(EQ. 24)
(EQ. 25)
(EQ. 26)
(EQ. 27)
IL
. The
ISL5586
Since the current relationships are different for constant
current versus constant voltage, the region of device
operation is critical to valid power dissipation calculations.
Reverse Active Mode
Overview
The reverse active mode (RA, 011) provides the same
functionality as the forward active mode. On hook transmission,
DC loop feed, and voice transmission are supported. Loop
supervision is provided by the switch hook detector. The device
may be operated from either high or low battery.
When in the Reverse Active mode the Tip and Ring DC
voltage characteristics exchange roles. That is, Ring is
typically 4V below ground and Tip is typically 4.5V more
positive than battery.
Silent Polarity Reversal
Changing from forward active to reverse active or vice versa
is referred to as polarity reversal. Many applications require
control of the polarity reversal transition time. Requirements
range from minimizing cross talk to protocol signalling.
The SLIC uses an external low voltage capacitor, C
set the reversal time. The capacitor is isolated from the AC
loop so that loop stability is not influenced by its selection.
Once C
constant over various load conditions.
The internal circuitry used to set the polarity reversal time is
shown in Figure 7. During Forward Active the switch is open
and the current from source I1 charges the external timing
capacitor C
function for the voltage at the POL node. When the Reverse
Active mode is initiated the switch closes and the difference
current (I2-I1) discharges the timing capacitor. The voltage at
the POL node drives one side of a transistor differential pair
which forces the Forward or Reverse condition on the Tip and
Ring amplifiers. The forward/reverse transition time is given by
Equation 28, where ∆time is the required reversal time.
Polarized capacitors may be used for C
at the POL pin and minimal voltage excursion in the order of
±0.75V, are well suited for polarized capacitors.
C
POL
=
POL
∆time
----------------
75000
POL
is set, the reversal time will remain nearly
. The internal resistor provides a clamping
POL
. The low voltage
November 3, 2004
POL
(EQ. 28)
FN4924.2
, to