Data Sheet
January 2000
L7556, L7557 Low-Power SLICs
with Battery Switch
Pin Information
(continued)
Table 1. Pin Descriptions
(continued)
Pin
11
12
13
14
15
Symbol Type
Description
PR
I/O
Protected Ring.
The output of the ring driver amplifier and input to loop sensing cir-
cuitry. Connect to loop through overvoltage protection.
CF2
—
Filter Capacitor 2.
Connect a 0.1 µF capacitor from this pin to AGND.
CF1
—
Filter Capacitor 1.
Connect a 0.47 µF capacitor from this pin to pin CF2.
VITR
O
Transmit ac Output Voltage.
This output is a voltage that is directly proportional to the
differential tip/ring current.
ICM
I
Common-Mode Current Sense.
To program ring ground sense threshold, connect a
resistor to V
CC
and connect a capacitor to AGND to filter 50/60 Hz. If unused, the pin
can be left unconnected.
RGDET
O
Ring Ground Detect.
When high, this open-collector output indicates the presence of
a ring ground. To use, connect a 100 kΩ resistor to V
CC
.
B0
I
State Control Input.
B0 and B1 determine the state of the SLIC. See Table 2.
AGND
—
Analog Signal Ground.
AGND
—
Analog Signal Ground.
DCR
I
dc Resistance for Low Loop Currents.
Leave open for dc feed resistance of 115
Ω,
or short to DCOUT for 615
Ω.
Intermediate values can be set by a simple resistor
divider from DCOUT to ground with the tap at DCR.
BGND
—
Battery Ground.
Ground return for the battery supply.
PT
I/O
Protected Tip.
The output of the tip driver amplifier and input to loop sensing circuitry.
Connect to loop through overvoltage protection.
RTSN
I
Ring Trip Sense Negative.
Connect this pin to the ringing generator signal through a
high-value resistor.
RTSP
I
Ring Trip Sense Positive.
Connect this pin to the ring relay and the ringer series resis-
tor through a high-value resistor.
NRDET
O
Ring Trip Detector Output.
When low, this logic output indicates that ringing is tripped.
NLC
O
Loop Detector Output.
When low, this logic output indicates an off-hook condition.
B1
I/O
State Control Input.
B0 and B1 determine the state of the SLIC. See Table 2. Pin B1
has a 40 kΩ pull-up. It goes low in the event of thermal shutdown.
XMT
O
Transmit ac Output Voltage.
The output of the uncommitted operational amplifier.
SN
I
Summing Node.
The inverting input of the uncommitted operational amplifier. A resis-
tor or network to XMT sets the gain.
NC
—
No Connection.
Do not use as a tie point.
BS2
—
Battery Switch Slowdown.
A 0.1 µF capacitor from BS1 to BS2 will ramp the battery
switch transition for applications requiring quiet transition. If not needed, the pin can be
left open.
BS1
—
Battery Switch Slowdown.
A 0.1 µF capacitor from BS1 to BS2 will ramp the battery
switch transition for applications requiring quiet transition. If not needed, the pin can be
left open.
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
Lucent Technologies Inc.
5
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