ST AN2118 APPLICATION NOTE

AN2118

Obsolete Product(s) - Obsolete Product(s)

Application note

STLC3075 single supply SLIC for

WLL application in buck-boost configuration

Introduction

The STLC3075 is a SLIC device specially designed for WLL (Wireless Local Loop) and ISDN terminal adapters.

This document contains a description of the device functions in buck-boost configuration, and provides some application hints. The device data sheet is an essential complement to this application note, providing important reference information that will simplify understanding of the content.

February 2007 Rev 3 1/21

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Content AN2118

Content

1 Wireless local loop system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2 Packaging . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

2.1 TQFP 10 mm x 10 mm x 1.4 mm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

3 Typical application schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.1 VBAT voltage generation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3.2 Operati on in off-hook condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.3 VPOS characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

3.4 Start-up and DC-DC converter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.5 Input curr ent limitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.6 VPOS current capability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.7 RSENSE settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.8 Trapezoidal ringing signal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.9 Ringer load . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.9.1 With European REN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.9.2 With USA REN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.10 Functioning at low VPOS (5.5 V) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

3.11 Effici ency and power dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3.12 Micro interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.13 Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.14 Ring trip . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

3.15 PCB precautions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.16 Ground configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

3.17 Capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.18 On-hook transmission . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.19 Phone detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3.20 ESD immunity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.21 Setting resistor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

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3.22 Longitudinal balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3.23 TTX filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

3.24 Gain settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

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AN2118 Content

3.25 Complex impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

4 Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

5 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

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Wireless local loop system AN2118

WLL SLIC

WLL

SLIC

1 Wireless local loop system

Figure 1. Wireless central office to premises diagram

WLL SLIC

☎

WLL SLIC

WLL

SLIC

☎

Central

office

Local loop

SLIC

Base station

transceiver

Final connection

by radio link

wireless

local loop

☎

PC00335

The main characteristics of this device consist in the capability to:

● operate with a single supply voltage in Buck-Boost or Fly-Back configuration (see

AN2132 for information on Fly-Back configuration).

● In Buck-Boost configuration, it can operate as in the standard STLC3055N

application, with a VPOS voltage in a range from +5.5 V to +12 V.

● generate negative battery voltage

● generate a ring signal (trapezoidal wave form)

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AN2118 Packaging

2 Packaging

The STLC3075 is housed in standard TQFP package plastic with copper lead frame. No copper slugs protrude from the plastic body. STLC3075 uses the “standard” package option.

The thermal resistances, shown in junction and the ambient still air, and are calculated or measured in ° C/W.

Table 1. Thermal resistance versus package size

Symbol Parameter Value Unit

Rth j-amb

Thermal resistance junction ambient (Full plastic TQFP on single layer board)

Thermal resistance junction ambient (Full plastic TQFP on four layer board)

Table 1

and

2.1 TQFP 10 mm x 10 mm x 1.4 mm

Theta (j-a) on boards, in still air.

Figure 2. Thermal resistance versus board structure

Figure 2

, are considered between the

70 ° C/W

45 ° C/W

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Typical application schematic AN2118

3 Typical application schematic

Figure 3. Typical application schematic

VPOS

CVCC

CVPOS

RSENSE

VPOS RSENSE

GATE

VBAT

CVB

CLK

TIP

RREF

CREV

RLIM

RING

CSVR CREV

RTH

RLIM

IREF

CRD

RING

D00TL489B

P-ch

RF1

RF2

TIP

CSVR

RTH

CCOMP

DET

CONTROL

INTERFACE

D1 D2 PD

TTX CLOCK

SUGGESTED GROUND LAY-OUT

SYSTEM GND

RRX

AGND

RS ZAC ZAC1

ZAC

VDD

RDD

RLV

CFL

GAIN SET

DET D0 D1 D2 PD CKTTX

CTTX1

CTTX2 FTTX

RTTX

AGND

BGND

PGND

CTTX

BGND

CAC

CVCC

ILTF

CAC

3.1 VBAT voltage generation

When operated with a positive supply voltage VPOS and a correctly set clock signal (typically 125 kHz), the SLIC generates a VBAT voltage for the active and ring operations.

The VBAT voltage level, with a 10% spread, is defined by the voltage divider RF1 / RF2 and can be set by choosing an RF1 value from a recommended set of values (see

Table 2. VBAT voltage values

RF1 (kΩ) VBAT (Active mode) VBAT (Ring mode)

270 -45.8 V -64.0 V 285 -48.2 V -67,4 V 300 -51.2 V -71.8 V 315 -54.0 V -75.3 V 330 -56.0 V -78.2 V

These values are referred to the device in active mode, on-hook condition (IL = 0 mA), and in ring mode without load.

The VBAT value must be chosen taking into account the absolute maximum ratings of the device (VBtot = 90 V). VBtot = (VBAT + VPOS) = 90 V must not be exceeded.

When ring mode is selected through the control interface, the VBAT voltage is increased by an internal circuit from it’s active level to a predetermined value for ring mode. These two

Table 2

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AN2118 Typical application schematic

voltage levels (VBAT active and VBAT ring) are hence correlated. When one is set, (ring or active), the other is also set at the same time.

3.2 Operation in off-hook condition

A major feature of this device is that when changing from on-hook to off-hook conditions (IL >0 mA), the VBAT voltage is automatically adjusted depending on the loop resistance and on the programmed current limitation value (ILIM).

It should be noted that the device is optimized to operate on short loop applications (RLOOP ≤ 500 Ω) in order to obtain the correct ring-tr i p detec ti on.

In these conditions, with line current reaching the programmed constant current feed value (ILIM), the STLC3075 works like a current generator with a fixed DC current.

A fixed voltage drop, 4 V on TIP/GND and approximately 6 V on RING/VBAT, assures the DC functionality and the proper swing for the AC signal.

When the line is set off-hook, the STLC3075 automatically adjusts the generated battery voltage (VBAT) to feed the line with a fixed DC current (programmable via RLIM), and so optimizes power dissipation.

Considering maximum and minimum values for RLOOP ranging from 500 to100 Ω, and with fixed parameters ILIM = 25 mA and 2Rp = 100 Ω, the battery voltage (VBAT) will be equal to:

1. VBAT = 25 mA x (500+100) + 10 V = - 25 V

2. VBAT = 25 mA x (100+100) + 10 V = - 15 V A correctly set current threshold (typically 9 mA), programmable by external resistor RTH,

allows the correct on/off hook transition function. During the off-hook dynamic transition, the CAC capacitor is charged. The line current

regulator system senses the current flowing into RD and reduces the ILOOP current to the programmed ILIM value, set by RLIM.

The settling time of the ILIM current is about 150 ms, and it is a function of the CAC splitter capacitor (min . value allowed is 22 µF).

3.3 VPOS characteristics

The input voltage VPOS can change slowly within the data sheet range (5.5 V - 12 V) without any effect on the VBAT voltage.

The STLC3075 can continue to operate correctly even if the VPOS voltage occasionally goes below 5.5 V (instantaneous value, not steady-state). The only limitation is the minimum voltage required on the external PMOS to keep it in a linear area.

Fast transients, ripples and spikes on the supply voltage V a reduced amplitude, depending upon the voltage supply rejection of the device.

Bench measurements on SVRR give -35 dB @ f = 50 Hz and -47 dB @ f = 4 kHz, using the test circuit configuration with the device in active mode, loaded with an RLOOP = 500 Ω, and ILIM = 25 mA.

will appear on TIP/RING with

POS

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