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User Manual
55 of 562
V 1.0
2021-08-25
XDPP1100 technical reference manual
Digital power controller
Current sense (IS)
3.3.5
Error tracking fault detection
Error tracking fault detects the inability of the IADC tracking mechanism to track the input. This fault typically
indicates a board-level problem, for instance one of the ISEN/IREF inputs is not connected properly. The
tracking fault detection is enabled by setting
ispX_track_fault_en
to 1.
The error tracking fault detection monitors the IADC quantizer output, which has six levels, ±1, ±3 and ±5. The
IADC
’s
ability to track the input can be estimated by comparing the number of ±5 samples relative to the
number of ±1 and ±3 samples.
The current sense tracking fault detection is based on a user-definable error ratio of ±5 to total samples, and it
can be set via register
ispX_err_ratio_sel
ispX_err_ratio_sel
programming including
the error threshold, the ratio of ±5 to total samples, as well as the minimum number of samples and time to
fault declaration. The minimum is based on a continuous stream of ±5 samples, which causes the tracking fault
counter to count up continuously with no intervening down counts.
Table 15
Current sense tracking error threshold
ispX_err_ration_sel Error threshold Error ratio (%) Min. samples to fault Min. time to fault (µs)
0
4
4/36 = 11.1
percent
124
4.96
1
8
8/40 = 20.0
percent
248
9.92
2
12
12/44 = 27.3
percent
372
14.88
3
16
16/48 = 33.3
percent
496
19.84
4
24
24/56 = 42.9
percent
744
29.76
5
32
32/64 = 50.0
percent
992
39.68
6
80
48/80 = 60.0
percent
1488
59.52
7
96
64/96 = 66.7
percent
1984
79.36
The error tracking fault detection is based on the operation of three counters:
•
Reference counter, cnt_ref, counts the number of ±1 and ±3 samples
•
Error counter, cnt_err, counts the number of ±5 samples
•
Tracking fault counter, cnt_track_fault, counts the tracking fault
If the error counter reaches the
ispX_err_ratio_sel
before the reference counter reaches 32, the tracking fault
counter is incremented. Correspondingly, in case the reference counter reaches 32 before the error counter
reaches the
ispX_err_ratio_sel
, the tracking fault counter is decremented. Thus, a tracking fault is declared if
the tracking fault counter reaches a count of 31.
Tracking fault is cleared only with shutdown via the EN pin or PMBus OPERATION command. However,
shutdown due to the tracking fault itself (or any other fault), without subsequent EN pin or OPERATION state
change, does not clear the fault. This is because tracking fault typically indicates a board-level problem such as
unconnected ISEN or IREF input.