Data Sheet
January 2000
L7556, L7557 Low-Power SLICs
with Battery Switch
Pin Information (continued)
Table 1. Pin Descriptions (continued)
Pin Symbol Type
Description
11
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.
12 CF2 — Filter Capacitor 2. Connect a 0.1 µF capacitor from this pin to AGND.
13 CF1 — Filter Capacitor 1. Connect a 0.47 µF capacitor from this pin to pin CF2.
14 VITR O Transmit ac Output Voltage. This output is a voltage that is directly proportional to the
differential tip/ring current.
15 ICM
I Common-Mode Current Sense. To program ring ground sense threshold, connect a
resistor to VCC and connect a capacitor to AGND to filter 50/60 Hz. If unused, the pin
can be left unconnected.
16 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 VCC.
17
B0
I State Control Input. B0 and B1 determine the state of the SLIC. See Table 2.
18 AGND — Analog Signal Ground.
19 AGND — Analog Signal Ground.
20 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.
21 BGND — Battery Ground. Ground return for the battery supply.
22
PT I/O Protected Tip. The output of the tip driver amplifier and input to loop sensing circuitry.
Connect to loop through overvoltage protection.
23 RTSN
I Ring Trip Sense Negative. Connect this pin to the ringing generator signal through a
high-value resistor.
24 RTSP
I Ring Trip Sense Positive. Connect this pin to the ring relay and the ringer series resis-
tor through a high-value resistor.
25 NRDET O Ring Trip Detector Output. When low, this logic output indicates that ringing is tripped.
26 NLC O Loop Detector Output. When low, this logic output indicates an off-hook condition.
27
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.
28 XMT O Transmit ac Output Voltage. The output of the uncommitted operational amplifier.
29
SN
I Summing Node. The inverting input of the uncommitted operational amplifier. A resis-
tor or network to XMT sets the gain.
30
NC
— No Connection. Do not use as a tie point.
31 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.
32 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.
Lucent Technologies Inc.
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