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UBA1707

Cordless telephone, answering machine line interface

Philips Electronics 

Philips Semiconductors

Cordless telephone, answering machine

line interface

Product specification

UBA1707

FUNCTIONAL DESCRIPTION

All data given in this chapter are typical values, except

when otherwise specified.

Supply (pins VCC and GND; bits PD and LSPD)

The UBA1707 must be supplied with an external stabilized

voltage source between pins VCC and GND.

Pins GND and LSPGND must be connected together.

Without any signal, with the loudspeaker channel enabled

at minimum volume and without any general purpose

switch selected, the internal current consumption is

2.2 mA at VCC = 3.3 V. Each selected switch

(pins SWI1, SWI2, or SWI3) increases the current

consumption by 600 µA.

The supply current can be reduced when the loudspeaker

channel is not used by switching it off (bit LSPD at logic 1).

The current consumption is then decreased by

approximately 800 µA at minimum volume.

To drastically reduce current consumption, the UBA1707

is provided with a power-down mode controlled by bit PD.

When bit PD is at logic 1, the current consumption from

VCC becomes 110 µA. In this mode, the serial interface is

the only function which remains active.

Line interface

DC CHARACTERISTICS (PINS LN, SLPE, REG, CST, LVI,

LCC, RGL AND GND; BIT CRC)

The IC generates a stabilized reference voltage (Vref)

between pins LN and SLPE. This reference voltage is

equal to 2.9 V, is temperature compensated and can be

adjusted by means of an external resistor (RVA). It can be

increased by connecting the RVA resistor between

pins REG and SLPE (see Fig.3).

The voltage at pin REG is used by the internal regulator to

generate the stabilized reference voltage and is decoupled

by a capacitor (CREG) which is connected to GND. This

capacitor, converted into an equivalent inductance

(see Section “Set impedance”) realizes the set impedance

conversion from its DC value (RSLPE) to its AC value

(ZSET in the audio-frequency range). Figure 4 illustrates

the reference voltage supply configuration. As can be seen

from Fig.4, part of the line current flows into the ZSET

impedance network and is not sensed by the UBA1707.

Therefore using the RVA resistor to change value of the

reference voltage will also modify all parameters related to

the line current such as:

• The automatic gain control

• The DC mask management

• The low voltage area characteristics.

In the same way, changing the value of ZSET also affects

the characteristics. The IC has been optimized for

Vref = 2.9 V and ZSET = 619 Ω.

8.5

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MGK706

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3.5

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103

104

105 RVA (Ω) 106

(1) Influence of RVA on Vref.

(2) Vref without influence of RVA.

Fig.3 Reference voltage adjustment with RVA.

The IC regulates the line voltage at pin LN which can be

calculated as follows:

VLN = Vref + RSLPE × ISLPE

ISLPE = Iline – IZSET – I* ≅ Iline – IZSET

Where:

Iline = line current

IZSET = current flowing through ZSET

I* = current consumed between LN and GND

(approximately 100 µA).

The preferred value for RSLPE is 10 Ω. Changing RSLPE will

affect more than the DC characteristics; it also influences

the transmit gain, the gain control characteristics, the

sidetone level and the maximum output swing on the line.

However, for compliance with CTR 21 8.66 Ω is the best

value for RSLPE.

1999 Feb 17

6

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