SH3000 SEMTECH [Semtech Corporation], SH3000 Datasheet - Page 6

• Manufacturer Part Number: SH3000
• Description: Low-Power Programmable Multifunction Support IC for Microcontrollers
• Manufacturer: SEMTECH [Semtech Corporation]

the reset interval, when V
some time, energy savings are realized and the startup
of the whole system is made easier. Commonly used
reset approach forces the processor to turn the oscillator
on and to run at full speed (thus consuming full power)
during the critical time when (possibly depleted) battery
is trying to raise V
the SH3000 allows the power source to charge the
bypass capacitors and raise the level of V
additional load. Only when power has stabilized is the
target micro permitted to start expending energy.
continues to provide the clock to the target processor,
but at a reduced frequency between 500 kHz and
1.0MHz. After a delay of 2 ms this clock is stopped,
automatically lowering the energy consumption of the
whole system, see Figure 2.
activations from noise and small power glitches on the
V
V
durations of the negative-going spikes.
to activate within 5 µs from the time V
Watchdog Timer
the watchdog timer. Whereas the low V
Detector monitors supply voltage, the watchdog timer
monitors behavior. It is based on a programmable timer
that must be restarted periodically by the host micro. If
software fails to restart the timer, the watchdog resets
the processor.
Copyright ©2003-2005 Semtech Corporation
SYSTEM MANAGEMENT
V
RST
N
CLK
DD
DD
RST
DD
Figure 2. Operations of low V
Since the clock is only active for the last 1 or 2 ms of
When a brownout event occurs, the SH3000
A Noise Filter (see Figure 1) prevents reset
When V
The second circuit for supervising the processor is
OUT
line. A typical behavior is shown in Figure 3 for the
level just above V
V
BO
1V
V
BO
DD
+ V
Undefined
HYST
is falling, both reset lines are guaranteed
Normal
DD
F
1ms
OUT
to an acceptable level. In contrast,
3-5ms
BO
DD
and various amplitudes and
has already been valid for
DD
2ms
Reduced F
0.5-1.0 MHz
12ms minimum
/ Brownout Detector
BO
DD
is crossed over.
DD
OUT
/ Brownout
2ms
with little
6ms
6
making it unlikely that it would occur accidentally, as
might happen for a simple pin-strobe configuration of a
typical watchdog IC.
disabled until initialized by the host processor.
to be selected (see Figure 1) and the 7-bit time-out
value to be set. As soon as the time-out is written, the
watchdog begins operations and can not be stopped;
also, the time-out value and or clock source can no
longer be changed.
are the internal 32 kHz clock and the CLK
out interval is programmable from 7.8125 ms to
1 second with resolution of 7.8125 ms. Internal 32 kHz
clock is running all the time, therefore the time-out
duration is fixed and predictable.
interval is programmable between 256 and 32768 cycles
of CLK
time-out duration is variable and depends both on the
frequency of CLK
target micro spends in the STOP mode, when the
CLK
programmable time-out value, allow the SH3000
exceptional flexibility, previously unattainable by existing
discrete watchdog solutions.
Restarting the timer takes considerable processing,
The watchdog is disabled after reset occurs. It stays
The initialization requires the watchdog clock mode
The two clock sources available for the watchdog
When operating from the 32 kHz source, the time-
When operating from the CLK
These two clock modes, together with the
OUT
Figure 3. Response to negative voltage spikes
OUT
10
signal is also stopped.
5
0
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
with resolution of 256 cycles. The actual
OUT
Guaranteed NO reset
signal and the amount of time the
SH3000 MicroBuddy™
Am plitude, V
V1.15
Guaranteed reset
OUT
Duration
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signal the time-out
OUT
signal.