Si3050 datasheet(35/128 Pages) SILABS

35 / 128 page

Si3050 + Si3011/18/19

Rev. 1.5

with the on-hook transition during pulse dialing. These

tests provide an inductive dc feed resulting in a large

voltage spike. This spike is caused by the line

inductance and the sudden decrease in current through

the loop when going on-hook. The traditional way of

dealing with this problem is to put a parallel RC shunt

across the hookswitch relay. The capacitor is large

(~1 µF, 250 V) and relatively expensive. In the Si3050,

loop current can be controlled to achieve three distinct

on-hook speeds to pass spark quenching tests without

additional BOM components. Through the settings of

four bits in three registers, OHS (Register 16), OHS2

(Register 31), SQ0, and SQ1 (Register 59), a slow ramp

down of loop current can be achieved which induces a

delay between the time the OH bit is cleared and the

time the DAA actually goes on-hook.

To ensure proper operation of the DAA during pulse

dialing, disable the automatic resistor calibration that is

performed each time the DAA enters the off-hook state

by setting the RCALD bit (Register 25, bit 5).

5.22. Receive Overload Detection

The Voice DAA chipset is capable of monitoring and

reporting receive overload conditions on the line. Billing

tones, parallel phone off-hook events, polarity reversals

and other disturbances on the line may trigger multiple

levels of overload detection as described below.

Transient events less than 1.1 VPK on the line are

filtered out by the low-pass digital filter on the Si3050 +

Si3011 and Si3050+Si3019. The ROV and ROVI bits

are set when the received signal is greater than 1.1

VPK. Both bits will continue to indicate an overload

condition until a zero is written to clear. The OVL mirrors

the function of the ROV and ROVI bits but it

automatically clears after the overload condition has

been removed. When the OVL bit returns to 0, the DAA

initiates an auto-calibration sequence that must

complete before data can be transmitted. An external

interrupt can optionally be triggered by the ROVI bit by

setting the ROVM and INTE bits.

Certain events such as billing tones can be sufficiently

large to disrupt the line-derived power supply of the

Voice DAA line side device (Si3011, Si3018 or Si3019.)

To ensure that the device maintains the off-hook line

state during these events, the BTE bit should be set. If

such an event occurs while the BTE bit is set, the BTD

and BTDI bits will be asserted. A zero must be written to

the BTE bit to clear the BTD and BTDI bits. An external

interrupt can optionally be triggered by the BTDI bit by

setting the BTDM and INTE bits.

In the event that a line disturbance causes the loop

current to collapse below the minimum required

operating current of the Voice DAA, the DOD and DODI

bits will be set. An external interrupt can optionally be

triggered by the DODI bit by setting the DODM and

INTE bits.

5.23. Billing Tone Filter (Optional)

Optionally, a billing tone filter may be inserted between

the line and the voice DAA to minimize disruptions

caused by large billing tones. The notch filter design

requires two notches, one at 12 kHz and one at 16 kHz.

Because these components are expensive and few

countries utilize billing tones, this filter is typically placed

in an external dongle or added as a population option.

Figure 25 shows a billing tone filter example. Table 19

gives the component values.

L1 must carry the entire loop current. The series

resistance of the inductors is important to achieve a

narrow and deep notch. This design has more than

25 dB of attenuation at both 12 kHz and 16 kHz.

Figure 25. Billing Tone Filter

The billing tone filter affects the DAA’s ac termination

and return loss. The global compromise complex ac

termination as selected by ACIM[3:0] = 1111 passes

global return loss specifications with and without the

billing tone filter by at least 3 dB. This ac termination is

optimized for frequency response and hybrid

Table 19. Component Values—Optional Billing

Tone Filters

Component

Value

C1,C2

0.027 µF, 50 V, ±10%

0.01 µF, 250 V, ±10%

3.3 mH, >120 mA, <10 , ±10%

10 mH, >40 mA, <10 , ±10%

RING

TIP

From Line

DAA

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