L9313 datasheet(26/40 Pages) AGERE

26 / 40 page

Data Sheet

September 2001

Full-Feature SLIC and Ringing Relay for TR-57 Applications

L9313 Line Interface and Line Access Circuit

Agere Systems Inc.

Applications (continued)

dc Characteristics (continued)

Power Control Resistor (continued)

Again assume:

TTSD – TAMBIENT(max) = allowed thermal rise

150

°C – 85 °C = 65 °C

Allowed thermal rise =

package thermal impedance x SLIC power dissipation

°C = 38 °C/W x SLIC power dissipation

Allowed SLIC power dissipation (PD) = 1.71 W

This time, assume a maximum ambient operating tem-

perature of 85

°C, a maximum current limit of 45 mA

(including tolerance), and a maximum battery of –56 V.

Again, assume a (worst-case) minimum dc loop of 0

Ω

and that 50

Ω protection resistors are used. Assume

the handset is 200

Ω:

Total PD = (56 V x 45 mA) + 0.100 W

Total PD = 2.34 W + 0.100 W

Total PD = 2.4375 W

Again, the power dissipated in the SLIC is the total

power dissipation less the power that is dissipated in

the loop.

SLIC PD = total power – loop power

Loop power = (ILIM)2 x (RLOOPdcmin + 2RP + RHANDSET)

Loop power = (45 mA)2 x (0

Ω + 100 Ω + 200 Ω)

Loop power = 0.6075 W

SLIC power = 2.4375 W – 0.6075 W

SLIC power = 1.83 W > 1.5 W

Under these extreme conditions, thermal margin is

increased via an external power control resistor.

The power dissipated in the power control resistor is

calculated by:

PPRW =

where in this example:

PPRW is power in the resistor

VBAT = –52 V

VLOOP = ILIM * (RLOOP + RPROT)

VROH is the ring-side overhead voltage of the SLIC.

Since this device is dc unbalanced, the tip side over-

head will remain typically at –2 V and the ring side over-

head will vary with the voltage at VOH. For the total tip/

ring default overhead of 5.5 V, the ring overhead is typi-

cally 3.5 V.

Overhead Voltage

Overhead is programmable in the active mode via an

applied voltage source at the device’s OVH control

input. The voltage source may be an external voltage

source or derived via a resistor divider network from

the VREF SLIC output or an external voltage source. A

programmable external voltage source may be used to

provide software control of the overhead voltage.

The overhead voltage (VOH) is related to the OVH volt-

age by:

VOH = 5.5 V + 5 x VOVH (V)

Overall accuracy is determined by the accuracy of the

voltage source and the accuracy of any external resis-

tor divider network used and voltage offsets due to the

specified input bias current. If a resistor divider from

VREF is used, lower magnitude resistor will give a more

accurate result due to a lower offset associated with

the input bias current; however, lower value resistors

will also draw more power from VREF. The sum of pro-

gramming resistors should be between 75 k

Ω and

200 k

Ω.

Note that a default overhead voltage of 5.5 V is

achieved by shorting input pin OVH to analog ground.

Internally, the SLIC needs typically 2 V from each sup-

ply rail to bias the amplifier circuitry. This can be

thought of as an internal saturation voltage.

The default overhead provides sufficient headroom for

on-hook transmission of a 3.14 dBm signal into 900

Ω.

3.14 = 10 log

V = 1.36 V, which is required over and above the inter-

nal saturation voltage for signal swing.

1.36 V + 4 V = 5.36 V < 5.5 V default overhead; thus, a

3.14 dBm into 900

Ω signal is passed without clipping

distortion.

The overhead voltage accuracy achieved will not only

be affected by the accuracy of the internal SLIC cir-

cuitry, but also by the accuracy of the voltage source

and the accuracy of any external resistor divider net-

work used.

In the scan mode, overhead is unaffected by VOVH and

internally fixed by the scan clamp circuitry to within the

specified limits.

VBAT

VROH

–

VLOOP

–

()2

RPWR

----------------------------------------------------------------------

0.9

---------

L9313 Datasheet(PDF) 26 Page - Agere Systems

L9313 Datasheet(HTML) 26 Page - Agere Systems

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Datasheet Download

Link URL