ISL5585FCRZ Intersil, ISL5585FCRZ Datasheet - Page 10

• Manufacturer Part Number: ISL5585FCRZ
• Description: SLIC 1-CH 53dB 45mA 3.3V/-18V/-24V/-28V 32-Pin QFN EP
• Manufacturer: Intersil

Specifications of ISL5585FCRZ

• Package: 32QFN EP
• Number Of Channels Per Chip: 1
• Polarity Reversal: Yes
• Longitudinal Balanced: 53(Min) dB
• Loop Current: 45 mA
• Minimum Operating Supply Voltage: 2.97|-16 V
• Typical Operating Supply Voltage: 3.3|-18|-24|-28 V
• Typical Supply Current: 9.3 mA

detection of ring trip or programmed off hook loop current,
whichever is greater.
To allow for proper ring trip operation, the transient current
limit setting should be set at least 25% higher than the peak
ring trip current setting. Setting the transient current 25%
higher should account for programming tolerances of both
the ring trip threshold and the transient current limit.
If loop current is larger than ring trip current (low REN
applications) then the transient current limit should be set at
least 35% higher than the loop current setting. The slightly
higher offset accounts for the slope of the loop current limit
function.
Attention to detail should be exercised when programming
the transient current limit setting. If ring trip detect does not
occur while ringing, then re-examine the transient current
limit and ring trip threshold settings.
DC Loop Feed
The feedback mechanism for monitoring the DC portion of
the loop current is the loop detector. A low pass filter is used
in the feedback to block voice band signals from interfering
with the loop current limit function. The pole of the low pass
filter is set by the external capacitor C
external capacitor should be 4.7µF, 6.3V rated polarized or
non-polarized capacitor.
Most applications will operate the device from low battery
while off hook. The DC feed characteristic of the device will
drive Tip and Ring towards half battery to regulate the DC
loop current. For light loads or Long Loops, Tip will be near
-4V and Ring will be near V
feed characteristic in terms of tip to ring voltage and loop
current.
The point on the y-axis labeled V
Tip to Ring voltage and is defined by the feed battery voltage
in Equation 6.
Figure 3 illustrates the actual loop current for a given set of
loop conditions. The loop conditions are determined by the
low battery voltage and the DC loop impedance. The DC
loop impedance is the sum of the protection resistance,
copper resistance (ohms/foot) and the telephone off hook
DC resistance.
V
TR OC
(
V
TR(OC)
)
=
FIGURE 2. DC FEED CHARACTERISTIC
V
BL
LONG LOOP
I
–
LOOP
9
(mA)
VBL
10
I
LIM
+ 5V. Figure 2 shows the DC
TR(OC)
SHORT LOOP
m = (∆V
DC
. The value of the
is the open circuit
TR
/∆I
L
) = 11.1kΩ
(EQ. 6)
ISL5585
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.
Process variations in the ISL5585 effect the I
11.11kΩ slope in Equation 8. All units are tested with: a
300Ω load across tip and ring, V
25mA. Equation 8 can be used to predict the ideal current at
this setting (25.76mA). All units are tested to be within
±8.5% of this ideal value (23.57mA to 27.95mA).
The maximum loop impedance for a programmed loop
current is defined as R
When R
constant current feed to constant voltage or resistive feed.
The line segment I
the load characteristic
Impedance Matching
The impedance of the device is programmed with the
external component R
the Transmit Amplifier that provides impedance matching. If
complex impedance matching is required, then a complex
network can be substituted for R
The feedback mechanism for monitoring the AC portion of
the loop current consists of two amplifiers, the Sense
Amplifier (SA) and the Transmit Amplifier (TA). The AC
feedback signal is used for impedance synthesis. A detailed
model of the AC feed back loop is shown in Figure 4.
I
I
R
I
SC
A
B
KNEE
=
=
FIGURE 3. I
I
=
LIM
V
----------------------- -
R
I
TR OC
LIM
I
LOOP
SC
=
KNEE
+
I
(
LIM
LIM
V
----------------------- -
V
--------------------------------------------------------------
+
TR OC
TR OC
2R
I
V
----------------------------------------------------- -
)
LIM
is the programmed current limit, 1760/R
A
CONSTANT CURRENT
TR OC
is exceeded, the device will transition from
P
(
(
LOOP
represents the constant current region of the
SHORT LOOP
(
R
11.11k
)
)
B
LOOP
11.11k
m=11.11k
–
)
represents the resistive feed portion of
R
vs. R
–
S
LOOP
KNEE
2R
. R
(Ω)
P
LOOP
S
I
LIM
I
.
LIM
is the gain setting resistor for
I
A
R
LOAD CHARACTERISTIC
SC
BAT
S
KNEE
.
.
CONSTANT VOLTAGE
RESISTIVE FEED
=-24V and I
LONG LOOP
I
m=Vtr(oc)/Rloop
B
OR
LIM
LIM
and
set to
(EQ. 10)
(EQ. 7)
IL
(EQ. 8)
(EQ. 9)
. The