
30169782
FIGURE 18. Sensor Diagnostic Flags Diagram
The
sensor
diagnostic
flags
are
located
in
the
SENDIAG_FLAGS register and are described in further de-
tails below.
SHORT_THLD_FLAG:
The short circuit threshold flag is used to report a short-circuit
condition. It is set when the output voltage (VOUT) is within
the absolute Vthreshold. Vthreshold can be programmed us-
ing the 8-bit SENDIAG_THLDH register.
For example, assume VREF = 5V, gain = 1, SENDIAG_THLD
= 0xDA (218d). In this case, Vthreshold can be calculated as:
Vthreshold = [(SENDIAG_THLD)(2)(VREF)] / [(Gain)(216)]
Vthreshold = [(218)(2)(5V)] / [(1)(216)]
Vthreshold = 33.3 mV
When
(-33.3mV)
≤ VOUT ≤ (33.3mV), then
SHORT_THLD_FLAG = 1; otherwise, SHORT_THLD_FLAG
= 0.
RAILS_FLAG:
The rails flag is used to detect if one of the sampled channels
is within 50mV of the rails potential (VA or VSS). This can be
further investigated to detect an open-circuit or short-circuit
condition. If the sampled channel is near a rail, then
RAILS_FLAG = 1; otherwise, RAILS_FLAG = 0.
POR_AFT_LST_RD:
If POR_AFT_LST_READ = 1, then there was a power-on re-
set since the last time the SENDIAG_FLAGS register was
read. This flag's status is cleared when this bit is read, unless
this bit is set again on account of another power-on-reset
event in the intervening period.
OFLO_FLAGS:
OFLO_FLAGS is used to indicate whether the modulator is
over-ranged or under-ranged. The following conditions are
possible:
1.
OFLO_FLAGS = 0x0: Normal Operation
2.
OFLO_FLAGS = 0x1: The modulator was not
overranged, but ADC_DOUT got clamped to 0x7FFF
(positive fullscale) or 0x8000 (negative full scale). For
example, if VREF = 5V, VIN = 2V, and gain = 128, then
OFLO_FLAGS would be 01b.
3.
OFLO_FLAGS = 0x2: The modulator was over-ranged
towards +VREF.
4.
OFLO_FLAGS = 0x3: The modulator was over-ranged
towards VREF.
The condition of OFLO_FLAGS = 10b or 11b can be used in
conjunction with the RAILS_FLAG to determine the fault con-
dition.
SAMPLED_CH:
These three bits show the channel number for which the
ADC_DOUT and SENDIAG_FLAGS are available. This does
not necessarily indicate the current channel under conversion
because the conversion frame and computation of results
from the channels are pipelined. That is, while the conversion
is going on for a particular channel, the results for the previous
conversion (of the same or a different channel) are available.
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