TDA7476_01 Datasheet, PDF (15/19 Pages) STMicroelectronics – CAR RADIO DIAGNOSTIC PROCESSOR

TDA7476
APPLICATION NOTES
s When single-ended devices are used and the application circuit is as shown in fig. 7,8, it is necessary
to use:
- a greater timing capacitor so that the time tm is high and the outputs of the amplifiers are able to rise over 1V;
- a resistor R_CS 1.5 times higher than that used for the bridge amplifiers.
In this case, the loudspeaker resistance ranges in which short circuit, normal operation and open load
are detected will be as follows:
S.C. across Load x Normal Operation x
Open Load
R_1,SE R_2,SE
R_3,SE
R_4,SE
D01AU1257
R1 ,SE
=
L_{----S----C----,-m----a---x-}
I_source
=
-^L---^S----^C----^,-^m----^a---^x-
54.45
⋅
R_CS
R2 ,SE
=
L_{----S----C----,-m----i-n-}
I_source
=
-^L---ⁿ---^o---^p---^,--^m----ⁱ-ⁿ-
54.45
⋅
R_CS
R3 ,SE
=
L_{----n---o---p---,--m----a---x}
I_source
=
-^L---ⁿ---^o---^p---^,--^m----^a---^x
54.45
⋅
R_CS
R4 ,SE
=
L_{----o---p---,--m----i-n-}
I_source
=
L_{----o---p---,--m----i-n-}
54.45
⋅
R_CS
For example, here below are two cases, with R_CS = 4.7kOhm and R_CS = 2.7kOhm.
S.C. across Load x Normal Operation x
Open Load
0Ω
0.43Ω 1.9Ω
19Ω 47Ω
infinite
S.C. across Load x Normal Operation x
Open Load
0Ω
0.24Ω 1.1Ω
11Ω 27Ω
infinite
D96AU501A
The exact values of the above mentioned resistive ranges may vary a little, depending on the power amplifier
used
In Permanent mode for single-ended devices as in fig. 7, 8 a short citcuit to ground is detected both when a
short to ground is really present and when the load is missing.
On single-ended devices as in figure 6, 8 if the loads are present then both in turn-on and in permanent diag-
nostic the fault present on one channel is pointed out for all the loads connected together.For example:
- see fig.8 if CH1+ is shorted to ground, the TDA7476 reveals a short to ground both for CH2 and for CH1.
- see fig.6 if CH1+ is shorted to ground, the TDA7476 detects a short circuit to ground for CH1, CH2, CH3, CH4.
About timing for the TDA7375, connected as in fig.7, Ct = 47µF if Cout = 1000µF, and Ct = 100µF if Cout =
2200µF.
If the circuit is as shown by fig. 8, the suggested values of Ct are as follows: Ct = 22µF if Cout = 1000µF,
Ct = 47µF if Cout = 2200µF.
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