2002 Jan 14
9
Philips Semiconductors
Preliminary specification
4
×
44 W into 4
Ω
or 4
×
75 W into 2
Ω
quad BTL car radio power amplifier
TDA8591J
7.2
Diagnostic output (DIAG)
The internal circuit of the diagnostic open-drain output is
shown in Fig.7.
A pull-up resistor is required if the diagnostic output is
connected to a microcontroller. Figure 8 shows four
possible solutions for fault diagnosis.
Figures 8a and 8b show simple configurations. The output
offset diagnostic cannot trigger the microcontroller
because of the 4-diode stack, only the temperature,
short-circuit and dynamic distortion diagnostic will give an
input LOW level for the microcontroller.
In Fig.8c, the diagnostic output is connected to an external
level shifter. Now DIAG pin output can also generate an
input LOW level for the microcontroller.
Assuming that a microcontroller HIGH input level must be
equal to, or greater than 2 V, the following equations are
used to calculate values for resistors R1 and R2:
V
IN1
> 2 V and
where:
5 V is the pull-up supply voltage
V
d
is the forward voltage of a diode (0.6 V)
R1 and R2 are the resistors in the level shifter.
Using both equations:
thus R1 > 3.3 R2
Therefore, R1 can be 47 k
Ω
and R2 can be 10 k
Ω
.
The level shifter shown in Fig.8d is used as a 2-bit
analog-to-digital converter.
With reference to Figs 7 and 8c, the truth table in Table 1
can be made:
Table 1
Truth table.
V
IN1
5 V
4
V
d
R2
5 V
4
V
d
×
–
R1
R2
+
-------------------------------
×
–
×
–
=
R1
2
R2
×
5 V
4
V
d
2
–
×
–
----------------------------------------
>
HIGH TEMPERATURE
OR SHORT-CIRCUIT OR
DDD
OFFSET
IN1
IN2
no
no
1
1
no
yes
0
1
yes
don’t care
0
0
handbook, halfpage
MGT610
≥
1
DIAG
PGND
temperature diagnostic
short-circuit diagnostic
dynamic distortion detection
output offset diagnostic
Fig.7 Internal circuit diagnostic output pin DIAG.
