UBA1707TS datasheet(15/36 Pages) PHILIPS

15 / 36 page

1999 Feb 17

Philips Semiconductors

Product speciﬁcation

Cordless telephone, answering machine

line interface

UBA1707

Fig.13 Loudspeaker channel.

Bit names are given in italics.

handbook, full pagewidth

MGK713

LSAI1

LSAI2

2Vd

LSPD

LSA2

LSA1

0.5VCC

DYNAMIC LIMITER

VOLUME CONTROL

VCC

UBA1707

DLCI

LSPD

VOL0

VOL2

DLC

LSPGND

LSAO

LSP

CDLC

CLSAO

DYNAMIC LIMITER (PIN DLC; BIT DLCI)

The dynamic limiter of the UBA1707 prevents clipping of

the loudspeaker output stage and protects the operation of

the circuit when the supply voltage at VCC falls below

2.7 V.

Hard clipping of the loudspeaker output stage is prevented

by rapidly reducing the gain when the output stage starts

to saturate. The time in which gain reduction is effected

(clipping attack time) is approximately a few milliseconds.

The circuit stays in the reduced gain mode until the peaks

of the loudspeaker signals no longer cause saturation.

The gain of the loudspeaker amplifier then returns to its

normal value within the clipping release time (typically

250 ms). Both attack and release times are proportional to

the value of the capacitor CDLC. The total harmonic

distortion of the loudspeaker output stage, in reduced gain

mode, stays below 5% up to 10 dB (minimum) of input

voltage overdrive [providing VLSAI is below

500 mV (RMS)].

When the supply voltage drops below an internal threshold

voltage of 2.7 V, the gain of the loudspeaker amplifier is

rapidly reduced (approximately 1 ms). When the supply

voltage exceeds 2.7 V, the gain of the loudspeaker

amplifier is increased again.

The hard clipping of the dynamic limiter can be inhibited by

setting the DLCI bit at logic 1, via the serial interface.

The dynamic limiter is no longer supplied by setting the

LSPD bit at logic 1. In this case, the CDLC capacitor charge

is maintained to allow the gain of the loudspeaker amplifier

to return to its nominal value as soon as the loudspeaker

channel is supplied again.

VOLUME CONTROL (BITS VOL0, VOL1 AND VOL2)

The loudspeaker amplifier voltage gain can be reduced in

steps of 3 dB via the serial interface (via bits VOL0, VOL1

and VOL2). These bits provide 7 steps of voltage gain

adjustment. The voltage gain is maximum when all bits are

at logic 1 and is reduced by 21 dB when all bits are at

logic 0.

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