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User Manual
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2021-08-25
XDPP1100 technical reference manual
Digital power controller
Voltage sense
2.3.2.2
V
RECT
watchdog timer
For correct V
RECT
measurement, the input voltage needs to have certain minimum value in order to trip the
vrs_comp comparator. Therefore, a watchdog timer (WDT) is started on the PWM rising edge. This timer
monitors the quality of the V
RECT
signal. The user can define a timeout threshold for the comparator via register
vrs_cmp_wdt_thr
. If no transition is observed at the comparator output after this time, the tracking ADC
proceeds by:
•
Preloading the previous tracking ADC DAC value
•
Waiting for the track start timer to complete
RECT
measurement cycle timing for the case where the vrs_comp transition is not
detected.
Figure 12
V
RECT
watchdog timeout
The following timer settings need to be considered:
•
Set the WDT count,
vrs_cmp_wdt_thr
, greater than the latest expected arrival time of the V
RECT
pulse at
VRSEN as measured from the PWM output.
•
Set the tracking start timer count,
vrs_track_start_thr
, to a value at minimum 250 ns greater than the WDT
to ensure adequate time for the AFE to settle after the V
RECT
pulse.
If significant ringing is observed on the VRSEN input pin at the V
RECT
pulse transition, the tracking start timer
should be set longer than the expected length of this ringing. Since both timers are started from the PWM rising
edge, the tracking start timer should always be larger than the WDT.
2.3.2.3
Deglitcher
The rising and falling edges of the measured V
RECT
signal can contain noise that might trip the comparator
prematurely. A deglitcher is added at the comparator output to prevent spurious signals from triggering the
hold phase within the V
RECT
measurement cycle.
PWM
VRSEN
vrs_comp_ref
vrs_comp
Hold Time
Tracking
Window
Tracking ADC active
Tracking ADC DAC held at code 0
Watchdog
Timeout
vrs_track_start_thr
vrs_cmp_wdt_thr
Tracking ADC DAC held at last sample
taken at PWM falling edge