TDA7571 Datasheet, PDF (15/21 Pages) STMicroelectronics – STPDACsw - Fully digital high efficiency power audio amplifier

TDA7571
Functions, pins and components description
4.3
Internal thermal protection network
The purpose of this function is to sense the chip temperature. Because of the power
dissipation of this device is almost constant (is not dependent by the output power), the
system must be designed to avoid chip temperature higher than 140 °C.
The internal thermal protection is intended to avoid dangerous situations due to, as
example, damaged power transistors (gate-source shorted) or bad environments conditions.
Through the internal thermal warning pin (THWINT, pin 36), a signal useful to switch-off the
system or, at least, reduce the power dissipation reducing (as example) the output power
and/or, in a system provided of regulated power supply, reducing the voltage supply of the
amplifier (±Vs) is present.
4.4
Feedback
The resistors Rgain-L1, Rgain-L2 for the Left channel and Rgain-R1, Rgain-R2 for the Right
channel defines the output AC voltage with a specific input digital data.
In the example, with 3.9Kohm and 1kohm, as shown in the schematic, the output voltage @
input = -6dBFS, is indicated in the Main characteristics description. These values are
needed to reach the clipping with 0dBFS input digital data and Vs = ±25V.
If different power supply values are used, different resistors can be used to guarantee the
clipping (then the output power), optimizing the signal to noise ratio.
If Vsmax is the maximum power supply at which the amplifier must goes into clipping
condition, the value of Rgain-X1 is given by:
R_g
a
i
n
–
X
1
–
(_---V_{----s---m-----a---x----}⋅_---R_{-----g---a---i--n----–----X---2-----–----}5_----._-1_-----⋅_---R_{-----g---a---i--n----–----X---2----})
5.1
Considering R_gain-X2 = 1kohm, the relation become:
R_{gain – X1}
=
(_---V_{----s---m-----a---x----–-----}5_---._--1_---)_-
5.1
As example, if V_smax = ±20V, R_gain - L1 = R_gain - R1 = 2.92kohm ~= 3kohm
4.5
Gate driving network
The main purpose of the 27 ohm resistors Rd-N-L, Rd-P-L, Rd-N-R and Rd-P-R are the
following:
1. Dumping of the L-C equivalent circuit done by the parasitic inductance and capacitance
present in the circuit
2. Reduction of the dv/dt of the Vgs and then reduction of the di/dt of the drain current of
the power MOS.
The R-C snubber network done by:
Rs-N-L, Cs-N-L
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