TDA8575 datasheet(5/16 Pages) PHILIPS

5 / 16 page

1996 Jul 29

Philips Semiconductors

Preliminary speciﬁcation

Ground noise isolation ampliﬁer

TDA8575

FUNCTIONAL DESCRIPTION

System description

To enable a high common mode rejection a new system

setup is used. The voltage to current converter, referred to

as V

→ I in the block diagram of Fig.1, replaces the

resistors that can be seen in the conventional system

solution.

Both systems are shown in Figs 4 and 5. In the

conventional system the common mode rejection is limited

by the matching properties of the resistors resulting in a

CMRR of 60 dB maximum. Using the new system setup a

CMRR of 80 dB is achieved.

Power on

In Fig.6 the preferred input capacitor values are shown.

If the capacitor C2 = 22

µF connected to the IN- inputs had

to be charged by the 0.5Vcc voltage source a charge time

would be required.

360 k

Ω

-------------------

µF

20s

This is inconvenient for most applications and therefore

the TDA8575(T) is equipped with a quick charge circuit.

On power-on the quick charge circuit charges the

capacitor C2 connected to the IN- pins. The quick charge

circuit consists of a voltage buffer and a control circuit

(referred to as ‘reference and power check’ in Fig.6) that

monitors the supply voltage VCC. If the supply voltage rises

more than

≈ 2 V the voltage buffer is switched on.

After charging C2 the voltage buffer is switched off.

The charge time of C2 will equal the charge time of C4, the

SVRR capacitor.

Fig.4 Conventional system.

handbook, halfpage

MGE830

0.5 VCC

Fig.5 New system using V

→ I converters.

handbook, halfpage

0.5 VCC

V I

I V

MGE831

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