
TDF8554J
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NXP B.V. 2011. All rights reserved.
Product data sheet
Rev. 1 — 31 August 2011
13 of 56
NXP Semiconductors
TDF8554J
4
45 W power amplifier with multiple voltage regulator
7.4.5 Thermal pre-warning and thermal protection
If the average junction temperature reaches one of the adjustable levels set via the
I2C-bus, selected with IB3[D4], pre-warning is activated resulting in pin DIAG LOW (if
selected) and can be read via the I2C-bus. The default setting for the thermal pre-warning
is IB3[D4] = 0, setting the warning level at Tj(AV)(pwarn) = 160 C.
If the temperature increases further, the temperature-controlled gain reduction is activated
for all four channels to reduce the output power; see
Figure 7. If this does not reduce the
average junction temperature, all four channels are switched off at the absolute maximum
temperature Toff.
7.5 Diagnostics
Diagnostic information can be read via the I2C-bus, but can also be made available at
pin DIAG. This information is seen at pin DIAG as a logical OR. In case of a failure,
pin DIAG remains LOW and the microcontroller can read the failure information via the
I2C-bus; pin DIAG can be used as a microcontroller interrupt to minimize I2C-bus traffic.
When the failure is removed, pin DIAG is released.
If the clip information is not needed, it can be removed from pin DIAG, enabling pin DIAG
to be used as an interrupt input for the microprocessor.
Fig 7.
Temperature controlled amplifier gain
001aam696
10
20
30
G
(dB)
0
Tj (°C)
140
190
180
160
170
150
Table 4.
Diagnostic information on pin DIAG
Diagnostic information
Pin DIAG
Power-on reset
after power-on reset; pin DIAG will remain LOW until amplifier
has started
Low battery
yes
Clip detection
can be enabled if IB4[D2] = 0
Temperature pre-warning
yes
Short-circuit outputs to battery,
ground or across the load
yes
Speaker fault detection
yes
Offset detection
no
Load detection
no