SI3021 datasheet(18/54 Pages) ETC

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Si 30 35

Rev. 1.2

Functional Description

The Si3035 is an integrated chipset that provides a

low-cost,

isolated,

silicon-based

interface

the

telephone line. The Si3035 saves cost and board area

by eliminating the need for a modem AFE or serial

codec. It also eliminates the need for an isolation

transformer, relays, opto-isolators, and a 2- to 4-wire

hybrid. The Si3035 solution requires only a few

low-cost,

discrete

components

achieve

full

compliance with FCC Part 68 and JATE out-of-band

noise requirements. See Figure 16 on page 15 for a

typical application circuit. See the pin-compatible

Si3034 or Si3044 data sheets for designs requiring

global support.

The Si3035 North America/Japan DAA offers a number

of new features not supported by the Si3032 device.

These include operation from a single 3.3 V power

supply, JATE (Japan) filter option, finer resolution for

both transmit and receive levels on AOUT (call progress

output), daisy-chaining for up to eight devices, and an

optional IIR filter. Table 15 summarizes the new Si3035

features.

Initialization

When the Si3035 is initially powered up, the RESET pin

should

asserted.

When

the

RESET

deasserted, the registers will have default values. This

reset condition guarantees the line-side chip (Si3012) is

powered down with no possibility of loading the line (i.e.,

off-hook). The following is an example initialization

procedure:

1. Program the PLLs with registers 7 to 9 (N1[7:0], M1[7:0],

N2[3:0] and M2[3:0]) to the appropriate divider ratios for

the supplied MCLK frequency and desired sample rate, as

defined in "Clock Generation Subsystem" on page 20.

2. Wait until the PLLs are locked. This time is between

100

µS and 1 ms.

3. Write an 0x80 into Register 6. This enables the charge

pump for the VA pin, powers up the line-side chip (Si3012),

and enables the AOUT for call progress monitoring.

After this procedure is complete, the Si3035 is ready for

ring detection and off-hook.

Isolation Barrier

The Si3035 achieves an isolation barrier through a

low-cost, high-voltage capacitor in conjunction with

Silicon

Laboratories’

proprietary

ISOcap

signal

processing techniques. These techniques eliminate any

signal

degradation

due

capacitor

mismatches,

common mode interference, or noise coupling. As

shown in Figure 16 on page 15, the C1, C2, and C4

capacitors isolate the Si3021 (DSP-side) from the

Si3012 (line-side). All transmit, receive, control, and

caller ID data are communicated through this barrier.

The ISOcap inter-chip communication is disabled by

default. To enable it, the PDL bit in Register 6 must be

cleared. No communication between the Si3021 and

Si3012 can occur until this bit is cleared. The clock

generator must be programmed to an acceptable

sample rate prior to clearing the PDL bit.

Off-Hook

The communication system generates an off-hook

command by applying logic 0 to the OFHK pin or writing

a logic 1 to bit 0 of control Register 5. The OFHK pin

must be enabled by setting bit 1 (OHE) of Register 5.

With OFHK at logic 0, the system is in an off-hook state.

This state is used to seize the line for incoming/outgoing

calls and can also be used for pulse dialing. With OFHK

at logic 1, negligible DC current flows through the

hookswitch. When a logic 0 is applied to the OFHK pin,

the hookswitch transistor pair, Q1 and Q2, turn on. The

net effect of the off-hook signal is the application of a

termination impedance across TIP and RING and the

flow of DC loop current. The termination impedance has

both an AC and a DC component.

The AC termination impedance is a 604-

Ω resistor,

which is connected to the TX pin. The DC termination is

a 51-

Ω resistor, which is connected to the DCT pin.

When executing an off-hook sequence, the Si3035

requires 1548/Fs seconds to complete the off-hook and

provide phone line data on the serial link. This includes

the 12/Fs filter group delay. If necessary, for the shortest

Table 15. New Si3035 Features

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