4
Le79555 Data Sheet
PIN DESCRIPTIONS
Pin Name
Type
Description
AGND
Gnd
Analog and Digital ground.
A(TIP)
Output
Output of A(TIP) power amplifier.
BATSW
Input
(VREG Switch Control) Input to switch VREG between on-chip switching regulator (input
Low) and VBAT2 (input High).
BGND
Gnd
Battery (power) ground.
B(RING)
Output
Output of B(RING) power amplifier.
C3
–
C1
Input
SLIC control pins. C3 is MSB and C1 is LSB.
CAS
Capacitor
Anti-Saturation pin for capacitor to filter reference voltage when operating in anti-
saturation region.
CHCLK
Input
(Chopper Clock) Input to switching regulator. f = 256 kHz (nominal)
CHS
Input
(Chopper Stabilization) Connection for external stabilization components.
D2
–
D1
Input
Relay Driver Control. D1 and D2 control the relay drivers RYOUT1 and RYOUT2. Logic
Low on D1 activates the RYOUT1 relay driver. Logic Low on D2 activates the RYOUT2
relay driver.
DA
Input
Negative input to ring-trip comparator.
DB
Input
Positive input to ring-trip comparator.
DET
Output
Switchhook Detector. A logic Low indicates that selected condition is detected. The
detect condition is selected by the logic inputs (C3
–
C1). The output is open-collector
with a built-in 15 k
pull-up resistor.
HPA
Capacitor
A (TIP) side of high-pass filter capacitor.
HPB
Capacitor
B (RING) side of high-pass filter capacitor.
L
Output
(Switching Regulator Power Transistor) Connection point for filter inductor and anode of
catch diode. This pin will have up to 60 V of pulse waveform on it, and it must be isolated
from sensitive circuits. Care must be taken to keep the diode connections short because
of the high currents and di/dt.
N/C
—
No Connect. This pin is not internally connected.
QBAT
Battery
(Quiet Battery) Filtered battery supply for the signal-processing circuits.
RD
Resistor
Detector threshold set and filter pin.
RDC
Resistor
Connection point for the DC feed current programming network. The other end of the
network connects to the receiver summing node (RSN).
RINGOUT
Output
Ring Relay Driver. Open-collector driver with emitter internally connected to BGND.
RSN
Input
Receive Summing Node. The metallic current (both AC and DC) between A(TIP) and
B(RING) is equal to 500 times the current into this pin. The networks which program
receive gain, two-wire impedance, and feed resistance all connect to this node.
RYOUT1
Output
Relay/Switch Driver. Open-collector driver with emitter internally connected to BGND.
RYOUT2
Output
Relay/Switch Driver. Open-collector driver with emitter internally connected to BGND.
VBAT
Battery
Most negative battery.
VBAT2
Battery
Battery supply to replace the VREG. Can be used to override switching regulator output,
enabled by BATSW (high).
VBREF
—
This is a Legerity reserved pin and must always be connected to the QBAT pin.
VCC
Power Supply
+5 V power supply.