TDA7572 Datasheet, PDF (41/64 Pages) STMicroelectronics – 200W mono bridge PWM amplifier with built-in step-up converter

TDA7572
7
Modulator
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
RQ
Aout
R1
MOD0
InvOut
Diff -To S.E.
R2
MOD1
HB1Out
VHB1OutF
Inv
SVR
InvIn
OSCOut
RQ
OSC
R1
MOD1
MOD2
HB2Out
R2
VHB2OutF
AC00017
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
V_-----P_----2_----._-5_--
RQ
>
V_-----A_----O_-----U_-----T_----m_-----a_----x_-
R1
+
V_-----S_----P_{------–----}V_-----S_----V_----R_---
R2
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.
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