TDF8544
NXP Semiconductors
I2C-bus controlled 4 50 W power amplifier
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. In legacy mode the
thermal pre-warning is also set 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 9. If this does not reduce the
average junction temperature, all four channels are switched off at the absolute maximum
temperature Toff.
001aam696
30
G
(dB)
20
10
0
140
150
160
170
180
190
T (°C)
j
Fig 9. Temperature controlled amplifier gain
7.5 Diagnostics
Diagnostic information can be read via the I2C-bus, but can also be made available at pin
DIAG or pin STB. Pin DIAG indicates information such as POR occurred, low battery, and
high battery; the output load fault information is selectable via the I2C-bus. 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.
To enable full control over the clipping information, pin STB can be programmed as a
second-clip detection pin. The clip detection level can be selected for all channels at once.
The clip information can be selected to be available separately at pin DIAG or at pin STB
for each channel. It is possible, for example,to distinguish between clipping of the front
and the rear channels.
The diagnostic information available at either of the two diagnostic pins DIAG and STB is
shown in Table 4.
TDF8544
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2011. All rights reserved.
Product data sheet
Rev. 2 — 29 August 2011
13 of 54
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