ATA6622(2008) データシートの表示（PDF） - Atmel Corporation
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ATA6622 Datasheet PDF : 29 Pages
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Figure 6-1.
VCC
3.3V/5V
Timing Sequence with RWD_OSC = 51 kΩ
NRES
Undervoltage Reset
treset = 4 ms
td = 155 ms
t1
t1 = 20.6 ms t2 = 21 ms
twd
NTRIG
Watchdog Reset
tnres = 4 ms
t2
ttrig > 200 ns
6.2 Worst Case Calculation with RWD_OSC = 51 kΩ
The internal oscillator has a tolerance of 20%. This means that t1 and t2 can also vary by 20%.
The worst case calculation for the watchdog period twd is calculated as follows.
The ideal watchdog time twd is between the maximum t1 and the minimum t1 plus the minimum
t2.
t1,min = 0.8 × t1 = 16.5 ms, t1,max = 1.2 × t1 = 24.8 ms
t2,min = 0.8 × t2 = 17.3 ms, t2,max = 1.2 × t2 = 26 ms
twdmax = t1min + t2min = 16.5 ms + 17.3 ms = 33.8 ms
twdmin = t1max = 24.8 ms
twd = 29.3 ms ±4.5 ms (±15%)
A microcontroller with an oscillator tolerance of ±15% is sufficient to supply the trigger inputs
correctly.
Table 6-1.
RWD_OSC
kΩ
34
51
91
120
Typical Watchdog Timings
Oscillator
Period
tosc/µs
13.3
Lead
Time
td/ms
105
Closed
Window
t1/ms
14.0
19.61
154.8
20.64
33.54 264.80 35.32
42.84 338.22 45.11
Open Window
t2/ms
14.7
21.67
37.06
47.34
Trigger Period from
Microcontroller Reset Time
twd/ms
tnres/ms
19.9
4
29.32
4
50.14
4
64.05
4
16 ATA6622/ATA6624/ATA6626
4986F–AUTO–07/08
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