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TEA0679T

I2C-bus controlled dual Dolby* B-type noise reduction circuit for playback applications

Philips Electronics 

Philips Semiconductors

I2C-bus controlled dual Dolby* B-type noise

reduction circuit for playback applications

Product specification

TEA0679T

handbook, full pagewINidPthUT

t

VC

upper threshold

lower threshold

t

OUTPUT

VHIGH

VLOW

tsw(P-M)

tsw(M-P)

tsw(P-M)

VC; integration capacitor voltage: tsw(P-M); switching time pause-to-music: tsw(M-P); switching time music-to-pause.

Fig.10 Blank skip timing diagram.

tsw(M-P)

t

MHB125

Soft head switching

In general the head switching procedure is recommended

to be performed in four steps:

1. Activate the mute function

2. Switch to the alternative head

3. Adjust the offset for the new head

4. Deactivate the mute function.

In applications without a mute function a soft head switch

via the I2C-bus can be realized using a capacitor

connected to pin 18. A proposal for this switching

mechanism is shown in Fig.11. To guarantee the internal

timing for the head switching operation an externally

connected device to pin 18 should not modify the output

current significantly.

An additional resistor is necessary if the head switching is

performed externally via the optional switching input

capability at pin 18. A proposal for this kind of switching is

shown in Fig.12.

In general soft head switching is only suitable if equal

offset values for head 1 and head 2 exist. A soft offset

value switching is not possible with the TEA0679T.

handbook, halfpage

pin 18

HS (optional)

10 µF

MHB126

Fig.11 Soft head switching via the I2C-bus.

handbook, halfpage

8 kΩ

IN1 IN2

pin 18

HS (optional)

10 µF

MHB127

Fig.12 External soft head switching.

1998 Nov 12

17

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