Si3232
Preliminary Rev. 0.96
19
Not
Recommended
fo
r N
ew
D
esi
4. Functional Description
The Si3232 dual SLIC is a low-voltage CMOS device
that provides a fully-programmable SLIC with line
monitoring and test functions to create a dual-channel
analog
telephone
interface.
Intended
for
multiple
channel
applications,
the
Si3232
provides
high
integration and low-power operation for applications,
such as integrated access devices (IADs), voice-over
DSL systems, cable telephony systems, and voice-over
IP systems. These devices meet all relevant Bellcore
LSSGR, ITU, and ETSI standards.
The Si3232 performs the battery, overvoltage, ringing,
supervision, hybrid, and test functions on-chip in a low-
power,
small-footprint
solution.
All
high-voltage
functions are implemented using the Si3200 linefeed
interface IC allowing a highly-integrated solution that
offers the lowest total system cost.
The internal linefeed circuitry provides programmable
on-hook voltage and off-hook loop current, reverse
battery operation, loop or ground start operation, and
on-hook transmission. Loop current and voltage are
continuously
monitored
using
an
integrated
8-bit
monitor A/D converter. The Si3232 provides on-chip,
balanced,
5 REN
ringing
with
or
without
a
programmable dc offset eliminating the need for an
external bulk ring generator and per-channel ringing
relay typically used in unbalanced ringing applications.
Both sinusoidal and trapezoidal ringing waveshapes are
available. Ringing parameters, such as frequency,
waveshape, cadence, and offset, can be programmed
into registers to reduce external controller requirements.
All ringing options are software-programmable over a
wide range of parameters to address a wide variety of
application requirements.
The Si3232 also provides a variety of line monitoring
and subscriber loop testing. It has the ability to
continuously monitor and store all line voltage and
current parameters for fault detection, and all values are
available in registers for later use. In addition, the
Si3232
provides
line
card
and
subscriber
loop
diagnostic functions to eliminate the need for system-
level test equipment. These test and diagnostic
functions are intended to comply with relevant LSSGR
and ITU requirements for line-fault detection and
reporting, and all measured values are stored in
registers for later use or further calculations.
The Si3232 is software-programmable allowing a single
hardware design to meet international requirements.
Programmability is supported using a standard 4-wire
serial peripheral interface (SPI). The Si3232 is available
in a 64-lead thin quad flat package (TQFP), and the
Si3200 is available in a thermally-enhanced 16-lead
SOIC.
4.1. Linefeed Architecture
The Si3232 is a low-voltage CMOS device that uses a
low-cost integrated linefeed interface IC to control the
high voltages required for subscriber line interfaces.
Figure 6 is a simplified single-ended model of the
linefeed control loop circuit for both the TIP and RING
leads.
The Si3232 uses both voltage and current sensing to
control TIP and RING. DC line voltages on TIP and
RING are measured through sense resistors RDC. AC
line voltages on TIP and RING are measured through
sense resistors RAC. The Si3232 uses the Si3200
linefeed interface to drive TIP and RING.
The Si3232 measures voltage at various nodes to
monitor the linefeed current. RDC and RBAT provide
access to these measuring points. The sense circuitry is
calibrated on-chip to guarantee measurement accuracy.
linefeed calibration.
4.2. Power Supply Transients on the
Si3200
The Si3200 features an ESD clamp protection circuit
connected between the VDD and VBATH rails. This
clamp protects the Si3200 against ESD damage when
the device is being handled out-of-circuit during
manufacture. Precautions must be taken in the VDD and
VBATH system power supply design. At power-up, the
VDD and VBATH rails must ramp-up from 0 V to their
respective target values in a linear fashion and must not
exhibit fast transients or oscillations which could cause
the ESD clamp to be activated for an extended period of
time resulting in damage to the Si3200. The resistors
shown as R20 through R23 together with capacitors
C23, C24, C30 and C31 in the Application Schematic
protection against in-circuit ESD clamp activation by
forming a filter time constant and by providing current
limitting action in case of momentary clamp activation
during power-up. These resistors and capacitors must
be included in the application circuit, while ensuring that
the VDD and VBATH system power supplies are
designed to exhibit start-up behavior that is free of
undesirable transients or oscillations. Once the VDD and
VBATH are in their steady state final values, the ESD
clamp has circuitry that prevents it from being activated
by transients slower than 10 V/us. In the steady
powered-up state, the VDD and VBATH rails must
therefore not exhibit transients resulting in a voltage
slew rate greater than 10 V/s.