HC55130IMZ datasheet(25/36 Pages) RENESAS

25 / 36 page

HC55120, HC55121, HC55130, HC55140, HC55142, HC55143, HC55150

FN4659 Rev 13.00

Page 25 of 36

June 1, 2006

Overload Levels and Silent Polarity Reversal

The pulse metering signal and voice are simultaneously

transmitted, and therefore require additional overhead to

prevent distortion of the signal. Reference section “Off hook

Overhead Voltage” to account for the additional pulse

metering signal requirements.

Most of the SLICs in the UniSLIC14 family feature full

polarity reversal. Full polarity reversal means that the SLIC

can transmit, determine the status of the line (on hook and

off hook) and provide “silent” polarity reversal. Reference

Equation 39 to program the polarity reversal time.

Interface to Dual and Single Supply

CODECs

Great care has been taken to minimize the number of external

components required with the UniSLIC14 family while still

providing the maximum flexibility. Figures 24A, 24B) shows

the connection of the UniSLIC14 to both a dual supply

CODEC/Filter and a single supply DSP CODEC/Filter.

To eliminate the DC blocking capacitors between the SLIC

and the CODEC/Filter when using a dual supply

CODEC/Filter, both the receive and transmit leads of the

SLIC are referenced to ground. This leads to a very simple

SLIC to CODEC/Filter interface, as shown in Figure 24A.

When using a single supply DSP CODEC/Filter the output

and input of the CODEC/Filter are no longer referenced to

ground. To achieve maximum voltage swing with a single

supply, both the output and input of the CODEC/Filter are

referenced to its own VCC/2 reference. Thus, DC blocking

capacitors are once again required. By using the PTG pin of

the UniSLIC14 and the externally supplied VCC/2 reference

of the CODEC/Filter, one of the DC blocking capacitors can

be eliminated (Figure 24B).

Power Management

The UniSLIC14 family provides two distinct power

management capabilities:

Power Sharing and Battery Selection

Power Sharing

Power sharing is a method of redistributing the power away

from the SLIC in short loop applications. The total system

power is the same, but the die temperature of the SLIC is

much lower. Power sharing becomes important if the

application has a single battery supply (-48V on hook

requirements for faxes and modems) and the possibility of

high loop currents (reference Figure 25). This technique

would prevent the SLIC from getting too hot and thermally

shutting down on short loops.

The power dissipation in the SLIC is the sum of the smaller

quiescent supply power and the much larger power that

results from the loop current. The power that results from the

loop current is the loop current times the voltage across the

SLIC. The power sharing resistor (RPS) reduces the voltage

across the SLIC, and thereby the on-chip power dissipation.

The voltage across the SLIC is reduced by the voltage drop

across RPS. This occurs because RPS is in series with the

loop current and the negative supply.

A mathematical verification follows:

FIGURE 23. PULSE METERING WITH TRANSHYBRID

BALANCE

VTX

VSPM

VTX

Vttx

125K

PTG

A = 1

UniSLIC14

OUTPUT BUFFER

150pF

C added to

bottom of

board

R added to

bottom of

board

500K

30.1K

FIGURE 24A.

FIGURE 24B.

FIGURE 24. INTERFACE TO DUAL AND SINGLE SUPPLY

CODECs

VTX

A = 1

VRX

UniSLIC14

VOUT

DUAL SUPPLY

CODEC/FILTER

GND

-5V

VTX

500K

PTG

A = 1

500K

VRX

UniSLIC14

SINGLE SUPPLY

CODEC/FILTER

GND

DSP

VIN

VOUT

VREF

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