TDA7572 datasheet(41/64 Pages) STMICROELECTRONICS

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TDA7572

Modulator

41/64

Modulator

The modulator PWM is the main function of device. Two modulators are provided which are

operated independently but configured for bridged mono operations. They are synchronized

by virtue of the common clock that drives them and operate as a three-state modulator

(phase shifting PWM modulation type) when the audio is inverted going to one modulator.

This inversion is accommodated by a dedicated inverter block present between the InvIn

and InvOut pin.

Figure 5.

Modulator block diagram

The above scheme reports the application circuits and internal block involved in the PWM

modulator. The analog signal is differential to single ended converted by the amplifier. The

signal obtained is inserted as current in the virtual ground of modulator MOD0. The

conversion is obtained trough R1 resistor. The same signal, output of AOUT, is inverted and

inserted in the virtual ground MOD1 through the resistor R1.

In order to obtain a PWM signal a square wave is inserted in both MOD0 and MOD1 through

the RQ resistor. The Gain of Modulator is equal to the ratio of R1/R2. In Order to choose the

value of RQ has to take into account the stability of modulator, guarantee if the following

relation is respected:

Equation 1

Clocked PWM modulators using an integrated T-network double integrator are implemented.

The end user has the ability to trade distortion for EMI by switching faster or slower,

controlled by PWMClock[1:0] in the modulator register.

SVR

InvOut

InvIn

OSCOut

MOD1

MOD2

HB1Out

HB2Out

VHB1OutF

VHB2OutF

Aout

OSC

Diff -To S.E.

Inv

MOD0

MOD1

AC00017

VP2.5

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

VAOUTmax

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

VSP

VSVR

–

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

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