ISL5585FCRZ Intersil, ISL5585FCRZ Datasheet - Page 9

• 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

Design Equations
Switch Hook Detect
The switch hook detect threshold is set by a single external
resistor, R
The term I
loop current threshold programming range is from 5mA to
15mA (40kΩ < R
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
current and the peak off hook current while still ringing.
In addition, the ring trip current must be set below the
transient current limit, including tolerances. The capacitor
C
Loop Current Limit
The loop current limit of the device is programmed by the
external resistor R
using Equation 3.
The term I
current limit programming range is from 15mA to 45mA
(39kΩ < R
Transient Current Limit
The drive current capability of the output tip and ring
amplifiers is programmed by an external resistor R
output current limit is separate from the DC loop current
limit function. The current limit circuit works in both the
source and sink direction, with an internally fixed offset to
prevent the current limit functions from turning on
simultaneously. The current limit function is provided by
sensing line current and reducing the voltage drive to the
load when the externally set threshold is exceeded, hence
forcing a constant source or sink current.
Transient Source Current Programming
The source current is externally programmed as shown in
Equation 4.
R
R
R
R
RT
SH
RT
IL
TL
, in parallel with R
=
=
=
=
1760
------------ -
I
1650
-------------
I
600 I
1800 I
LIM
SRC
SH
RT
SH
LIM
IL
⁄
<117kΩ).
. Equation 1 is used to calculate the value of R
. I
⁄
SH
is the desired DC loop current threshold. The
is the desired loop current limit. The loop
RT
RT
SH
should be set between the peak ringing
IL
<120kΩ).
. The value of R
RT
, will set the ring trip response time.
9
IL
can be calculated
TL
(EQ. 1)
(EQ. 2)
(EQ. 3)
(EQ. 4)
. This
SH
ISL5585
.
For example a source current limit setting of 95mA is
programmed with a 18.7kΩ (R
TL pin of the device to ground. This setting determines the
maximum amount of current which flows from Tip to Ring
during an off hook event until the DC loop current limit
responds. In addition this setting also determines the amount
of current which will flow from Tip or Ring when external
battery faults occur.
Transient Sink Current Programming
The sink current limit is internally offset 20% higher than the
externally programmed source current limit setting.
If the source current limit is set to 95mA, the sink current limit
will be 114mA. This setting will determine the maximum current
that flows into Tip or Ring when external ground faults occur.
Understanding Transient Current Limit
Each tip and ring amplifier is designed to limit source current
and sink current. Figure 1 shows the functionality of the
circuit for the case of limiting the source current. A similar
diagram applies to the sink current limit with current polarity
changed accordingly.
During normal operation, the error current (I
the output voltage is determined by the signal current (I
multiplied by the 200K feedback resistor. With the current
polarity as shown for I
positivewith respect to half battery. Assuming the amplifier
output is driving a load at a more negative potential, the
amplifier output will source current.
During excessive output source current flow, the scaled
output current (I
forcing an error current (I
the error current subtracts from the signal current, which
reduces the amplifier output voltage. By reducing the output
voltage the source current to the load is decreased and the
output current is limited.
Setting the Proper Transient Current Limit
Since this feature programs the maximum output current of
the device, the setting must be high enough to allow for
I
SNK
TIP or RING
I
O
FIGURE 1. CURRENT LIMIT FUNCTIONAL DIAGRAM
=
1.20
×
I
SRC
O
200K
20
/K) exceeds the reference current (I
I
O
SIG
/K
ERR
, the output voltage moves
). With the polarity as shown
TL)
I
ERR
resistor connected from the
+
-
VB/2
I
SIG
ERR
) is zero and
I
REF
= 1.21/TL
REF
(EQ. 5)
SIG
)
)