SI3233 datasheet(19/100 Pages) SILABS

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Si3233

Preliminary Rev. 0.5

2.2.2. Linefeed Architecture

The Si3233 uses either the Si3201 linefeed interface IC

or a low-cost external circuit to generate the high

voltages required for subscriber line interfaces.

The ProSLIC uses both voltage and current sensing to

control TIP and RING. DC and AC line voltages on TIP

and RING are measured through sense resistors R1/R3

and R8/R9, respectively.

The ProSLIC measures voltage at various nodes in

order to monitor the linefeed current. The sense circuitry

is calibrated on-chip to guarantee measurement

accuracy with standard external component tolerances.

See "2.2.9. Linefeed Calibration" on page 23 for details.

2.2.3. Linefeed Operation States

The ProSLIC linefeed has eight states of operation as

shown in Table 20. The state of operation is controlled

using the Linefeed Control register (direct Register 64).

The open state turns off all currents into the external

bipolar transistors and can be used in the presence of

fault conditions on the line and to generate Open Switch

Intervals (OSIs). TIP and RING are effectively tri-stated

with a dc output impedance of about 150 k

Ω. The

ProSLIC can also automatically enter the open state if it

detects excessive power being consumed in the

external

bipolar

transistors.

See

"2.2.5.

Power

Monitoring and Line Fault Detection" on page 21 for

more details.

In the forward active and reverse active states, linefeed

circuitry is on and the audio signal paths are powered

down during an on-hook loop condition.

In the forward and reverse on-hook transmission states

audio signal paths are powered up to provide data

transmission during an on-hook loop condition.

The TIP Open state turns off all control currents to the

line driver devices connected to TIP and provides an

active linefeed on RING for ground start operation.

The RING Open state provides similar operation with

the RING drivers off and TIP active.

The

ringing

state

drives

programmable

ringing

waveforms onto the line.

2.2.4. Loop Voltage and Current Monitoring

The ProSLIC continuously monitors the TIP and RING

voltages and external BJT currents. These values are

available in registers 78–89. Table 21 on page 20 lists

the values that are measured and their associated

registers. An internal A/D converter samples the

measured voltages and currents from the analog sense

circuitry and translates them into the digital domain. The

A/D updates the samples at an 800 Hz rate. Two

derived values are also reported—loop voltage and loop

current. The loop voltage, VTIP –VRING, is reported as a

1-bit sign, 6-bit magnitude format. For ground start

operation the reported value is the RING voltage. The

loop current, (IQ1 – IQ2 + IQ5 –IQ6)/2, is reported in a 1-

bit sign, 6-bit magnitude format. In RING open and TIP

open states the loop current is reported as (IQ1 – IQ2) +

(IQ5 –IQ6).

Table 19. Programmable Ranges of DC

Linefeed Characteristics

Parameter

Programmable

Range

Default

Value

Bits

Location*

ILIM

20 to 41 mA

20 mA

ILIM[2:0]

Direct

VOC

0 to 94.5 V

48 V

VOC[5:0]

Direct

VCM

0 to 94.5 V

3 V

VCM[5:0]

Direct

*Note:

The ProSLIC uses registers that are both directly

and indirectly mapped. A “direct” register is one that

is mapped directly.

SI3233 Datasheet(PDF) 19 Page - Silicon Laboratories

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