1999 Feb 17

14

Philips Semiconductors

Product specification

Cordless telephone, answering machine

line interface

UBA1707

Auxiliary amplifier (pins AXI and AXO; bit AXM)

The auxiliary amplifier (see Fig.12) has one input (AXI) and one output (AXO). The input impedance between pins AXI

and GND is 3.8 k

Ω. The rail-to-rail output stage is designed to drive a 500 µA peak current. The output impedance at pin

AXO is approximately 100

Ω.

The output as well as the input are biased at 2

at 31.8 dB.The amplifier can be muted by setting bit AXM at logic 1 via the serial interface. In this case, the input

impedance between pins AXI and GND is infinite.

Fig.12 Auxiliary amplifier.

handbook, full pagewidth

MGK712

AXM

2Vd

AXI

AXO

UBA1707

Bit names are given in italics.

Loudspeaker channel (see Fig.13)

The loudspeaker amplifier has two symmetrical inputs

LSAI1 and LSAI2 selectable independently by the bits

LSA1 and LSA2 respectively. The input impedance

between pins LSAI1or LSAI2 and GND is typically 21 k

Ω.

Each of these two inputs stages can accommodate signals

up to 500 mV (RMS) at room temperature for less than 2%

of Total Harmonic Distortion (THD) at minimum voltage

gain.

The inputs are biased at 2

(whatever the state of bits LSA1 and LSA2).

The rail-to-rail output stage is designed to power a

loudspeaker connected as a single-ended load (between

pins LSAO and LSPGND). The output LSAO is able to

drive at least a 150 mA peak current.

As a result, it can drive loudspeaker loads down to 8

Ω at

In order to avoid crosstalk from the loudspeaker to other

amplifiers, the loudspeaker current flows via pin LSPGND.

This pin must be externally connected to pin GND.

The nominal value of the voltage gain for maximum

volume from pins LSAI1 or LSAI2 to pin LSAO is set at

28 dB.

This amplifier is no longer supplied by setting the LSPD bit

at logic 1 via the serial interface.