MAX13301 Datasheet, PDF (30/37 Pages) Maxim Integrated Products – 4-Channel, Automotive Class D Audio Amplifier Feedback After the Filter

4-Channel, Automotive Class D Audio Amplifier
Tweeter Diagnostic
This diagnostic detects whether a tweeter is properly
connected when a passive crossover is used. To detect
the presence of a tweeter load, the device should be
in play mode. Set CTRL3.TW (tweeter-detect current
threshold setting bit) to 1 and apply a 15kHz to 25kHz
sinusoidal signal to all the inputs. The devices compare
the load current to the tweeter-detect current threshold. If
the load current exceeds the threshold, the correspond-
ing OSTAT1.LOAD[3:0] (load indicator bit) is set to 1,
indicating that there is a tweeter. The amplitude of the
input signal depends on the impedance vs. frequency
characteristics of the tweeter. Correct tweeter detec-
tion requires that the amplitude be large enough to trip
the tweeter-detect current threshold when a tweeter is
present. The tweeter-detect current threshold depends
on the programmed current limit as set by CTRL3.HCL
bit. See the Low-Current Threshold parameter in the
Electrical Characteristics table.
Note that the OSTAT1.LOAD[3:0] bits do not latch high
upon detecting a tweeter. During zero crossings, the
load current does not exceed the threshold and the
OSTAT1.LOAD[3:0] bits are cleared to 0. There are two
ways to obtain the results of the tweeter diagnostic:
1) Continuously read the OSTAT1.LOAD[3:0] bits to
determine if any have been set high.
2) The open-drain CL0 output can also be monitored if
MAP.LCTM (low-current threshold map bit) is set to 1
(setting this bit to 1 maps OSTAT1.LOAD[3:0] to the
CL0 output). Because CL0 is the NORed function of
the OSTAT1.LOAD[3:0] bits, CL0 pulls low if a short
exists on any of the outputs.
After running the diagnostic, clear CTRL3.TW to 0 to
disable tweeter diagnostic and clear MAP.LCTM to 0 to
unmap the OSTAT1.LOAD[3:0] bits to the CL0 output.
Doing so prevents CL0 from being asserted when the
tweeter-detect current threshold is exceeded during play.
Tweeter diagnostic is done on all outputs. The presence
of a tweeter is traceable to any output by examining the
OSTAT1.LOAD[3:0] bits. The presence of a tweeter on
output 3 causes LOAD3 to go high, the presence of a
tweeter on output 2 causes LOAD2 to go high, etc.
Continuous Diagnostics
The device constantly monitors critical performance
and safety parameters such as output offset voltages,
output clipping, thermal faults, and undervoltage and
overvoltage conditions. The results are reported and
continuously updated in the status registers (STAT and
OSTAT[3:0]).
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Offset Diagnostic
Run the offset diagnostic to determine if there is an
offset between the differential outputs. To do so, place
the device in play mode and apply no input signals. The
results of this diagnostic are reported in OSTAT3.VOS[3:0]
(offset voltage indicator bits). OSTAT3.VOS[3:0] indicates
whether the offset voltage is less than or greater than the
offset voltage threshold. The differential offset threshold is
Q1V (typ) for the MAX13301.
Clipping Diagnostic
Use the clipping diagnostic to detect clipping outputs.
Program CTRL1.CLVL[1:0] (clip level bit) for a threshold
of either 1%, 3%, 5%, or 10% THD+N. Clip indication is
provided by OSTAT0.CLIP[3:0] (clip indicator bit). These
bits are set to 0 only during the times when an overdriven
output is actually clipping. A clipping output indicator is
available for each output: CLIP3 is for output 3, CLIP2
is for output 2, etc. The open-drain outputs, CL0 and
MUTE_CL1, also provide clip indication.
Thermal Warning Diagnostic and Thermal Shutdown
If the junction temperature exceeds the programmed
temperature limit, then a temperature warning is set
immediately (i.e., STAT.OTW goes low). The device does
not act upon a temperature fault to the programmed limit.
The temperature fault self clears when the temperature
drops below the threshold. The programmed tem-
perature limit is set by CTRL0.TW[1:0] (thermal warning
threshold bits) from +110NC to +140NC in 10NC incre-
ments. Overtemperature warning by the hardware is
also possible by setting both the MAP.OTWM (overtem-
perature warning map) and MAP.OTM (overtemperature
shutdown mask) to 1 to map the STAT.OTW (overtem-
perature warning) bit to the FLT_OT output.
If the junction temperature exceeds +150NC, the device
disables all channels and the STAT.OT (overtemperature
shutdown) bit asserts low. The digital interface remains
active and the contents of the registers are unchanged.
When the die temperature drops below +140NC, normal
operation is restored. Thermal shutdown indication by
hardware is also possible by setting MAP.OTM (over-
temperature shutdown map bit) to 1 to map the STAT.OT
(overtemperature shutdown bit) to the FLT_OT output.
Charge-Pump Undervoltage Diagnostic
The device drives the high-side FETs with the aid of
a charge pump. The charge pump charges the hold
capacitor CHOLD to 5V at the end of each switching
cycle. When the voltage on CHOLD falls below 3.87V,
the devices assert STAT.CPUV (charge-pump under-
voltage indicator bit) and three-state all outputs. The