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CY8C28xxx PSoC Programmable System-on-Chip TRM, Document No. 001-52594 Rev. *G
Sleep and Watchdog
In practical application, it is important to know that the
watchdog timer interval can be anywhere between two and
three times the sleep timer interval. The only way to guaran-
tee that the WDT interval is a full three times that of the
sleep interval is to clear the sleep timer (write 38h) when
clearing the WDT register. However, this is not possible in
applications that use the sleep timer as a real-time clock. In
the case where firmware clears the WDT register without
clearing the sleep timer, this can occur at any point in a
given sleep timer interval. If it occurs just before the terminal
count of a sleep timer interval, the resulting WDT interval will
be just over two times that of the sleep timer interval.
12.5
Power Consumption
Sleep mode power consumption consists of the items in the
following tables.
In
, the typical block currents shown do not repre-
sent maximums. These currents do not include any analog
block currents that may be on during Sleep mode.
While the CLK32K can be turned off in Sleep mode, this
mode is not useful because it makes it impossible to restart
unless an imprecise power on reset (IPOR) occurs. (The
Sleep bit can not be cleared without CLK32K.) During the
sleep mode buzz, the bandgap is on for two cycles and the
LVD circuitry is on for one cycle. Time-averaged currents
from periodic sleep mode ‘buzz’, with periodic count of N,
are listed in
lists example currents for N=256 and N=1024.
Device leakage currents add to the totals in the table.
Table 12-5. Continuous Currents
IPOR
1
A
ICLK32K (ILO/ECO)
1
A
Table 12-6. Time-Averaged Currents
IBG (Bandgap)
(2/N) * 60
A
ILVD (LVD comparators)
(2/N) * 50
A
Table 12-7. Example Currents
N = 256
N = 1024
IPOR
1
1
CLK32K
1
1
IBG
0.46
0.12
ILVD
0.4
0.1
Total
2.9
A
2.2
A
Summary of Contents for CY8C28 series
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