ST AN2118 APPLICATION NOTE

AN2118

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.

Product(s) -Obsolete

Product(s) Obsolete

February 2007

Rev 3

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www.st.com

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

3.2

3.3

3.4

3.5

3.6

3.7

3.8

3.9

3.10

3.11

3.12

3.13

3.14

3.15

3.16

Obsolete3.17

3.18

3.19

3.20

3.21

3.22

3.23

3.24

	VBAT voltage generation . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . . .	. 6
	Operation in off-hook condition . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . . .	. 7
	VPOS characteristics . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . . .	7
	Start-up and DC-DC converter . . . . . . . . . . . . . .		Product(s). . . . . . . . . . . . . . . . . . . .	8
	Input current limitation			8
			. . . . . . . . . . . . . . . . . . . .
	VPOS current capability . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . . .	9
	RSENSE settings . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . . .	9
	Trapezoidal ringing signal . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . . .	9
	Ringer load . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	10
	Efficiency and power dissipationObsolete. . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	11
	3.9.1	With European REN . . . . . . . . . . . . . . . . .	. . . . . . . . . . . . . . . . . . . . . .	10
	3.9.2	With USA REN . . . . . . . . . . . . . . . . . . . . . .	. . . . . . . . . . . . . . . . . . . . . .	10
	Functioning at low VPOS (5.5 V) . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	10
		-		15
	Product(s)Ground configuration . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .
	Micro interface . . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	13
	Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	13
	Ring trip	. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . . . . . . . . . . . . . . . . .	14
	PCB precautions . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	15
	Capacitor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	16
	On-hook transmission . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	16
	Phone detection . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	16
	ESD immunity . . . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	17
	Setting resistor . . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	17
	Longitudinal balance . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	17
	TTX filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	18
	Gain settings . . . . . . . . . . . . . . . . . . . . . . . . . . .		. . . . . . . . . . . . . . . . . . .	18

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AN2118		Content
	3.25 Complex impedance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . . 18
4	Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . 20
5	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	. . . 20

Product(s) -Obsolete

Product(s) Obsolete

3/21

Wireless local loop system	AN2118

1 Wireless local loop system

Figure 1. Wireless central office to premises diagram

									WLL
									SLIC
									WLL
		Central							SLIC
					Base station
		office			transceiver
			SLIC						WLL
									SLIC
					Final connection
					by radio link
		Local loop			=
					wireless
					local loop
											PC00335
● generate negative battery voltage							Product(s)
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.
				Obsolete
● generate a ring signal (trapezoidal wave form)
-
	Product(s)
Obsolete

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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 Table 1 and Figure 2, are considered between the 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	70	° C/W
		(Full plastic TQFP on single layer board)
Rth j-amb		Thermal resistance junction ambient	45	° C/W
		(Full plastic TQFP on four layer board)

2.1TQFP 10 mm x 10 mm x 1.4 mm

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

Figure 2. Thermal resistance versus board structure

Product(s)

Obsolete

Product(s)

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Typical application schematic	AN2118

3 Typical application schematic

	Figure 3.	Typical application schematic
						CVCC		VPOS
							CVPOS
				RX	TX			RSENSE
			RRX
			RS	RX	TX AGND BGND	CVCC		VPOS
				RS				RSENSE
										Q1
				ZAC				GATE		P-ch
			CCOMP	ZAC1						D1
								VBAT
			ZAC
			ZA						CVB	RF1
				ZB				VF		L
			CH ZB							CV
										RF2
			VDD
			RDD	GAIN SET				CLK CLK
									RP
								TIP		TIP
								RING	RP	RING
			DET	DET
		CONTROL
			D0	D0
		INTERFACE						CSVR
			D1	D1
								CREV
			D2	D2
									CREV	CSVR
			PD	PD
		TTX CLOCK		CKTTX				RTH
			RLV	CTTX1				RLIM
			CS					IREF
			RLV	CTTX2
				FTTX					RREF RLIM	RTH
					RTTX CAC	ILTF RD			Product(s)
			CFL
				RTTX			RD	CRD		D00TL489B
			AGND
			BGND		CTTX	CAC
			SYSTEM GND
		SUGGESTED GROUND LAY-OUT
			PGND	Obsolete
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):
	Product(s)
	Table 2.	VBAT voltage values
		RF1 (kΩ)		VBAT (Active mode)						VBAT (Ring mode)
		270			-45.8 V					-64.0 V
Obsolete		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

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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.

3.2Operation 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-trip detection.

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.	Product(s)
	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
		Obsolete
	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
	Product(s)	µF).
	capacitor (min. value allowed is 22
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.
Obsolete
	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 VPOS will appear on TIP/RING with 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.

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