SH3000UM SEMTECH [Semtech Corporation], SH3000UM Datasheet - Page 11

• Manufacturer Part Number: SH3000UM
• Manufacturer: SEMTECH [Semtech Corporation]

Low V
On power up both the active-high and active-low reset sig-
nals are driven active. These outputs are typically valid for
a V
a V
The reset outputs remain active until V
above the level of (V
fi xed amount of hysteresis, nominally 50mV, added to pre-
vent nuisance reset activations (when V
near the level of V
present).
At the level of (V
ered valid. In case of the initial power-up, the reset is then
driven inactive once 6ms of valid power have elapsed. In
the case of brownout, the reset is released after a de-
lay of 6ms (but no less than 12ms from the beginning of
the brownout). Such a fast reset is possible because the
SH3003 provides a fast-starting clock that is free of crys-
tal start-up time requirements. This gives the SH3003 an
advantage over most external reset circuits, which must
have a long reset pulse duration to accommodate long
and unpredictable crystal start-up times.
The SH3003 guarantees that a valid and stable clock is
available 2ms before the reset signals are negated, so
that internal synchronous reset and initialization of the
target micro can proceed normally.
©2006 Semtech Corp.
POWER MANAGEMENT
POWER MANAGEMENT
Application Information
DD
DD
V
RST
N
CLK
RST
Figure 2. Operations of low V
DD
level of at least 0.5V, and guaranteed to be valid for
level of 1.0V.
DD
OUT
V
Reset (continued)
BO
1V
V
BO
+ V
Undefined
HYST
BO
BO
Normal
F
+ V
1 ms
and some noise or power glitching is
OUT
BO
3-5 ms
HYST
+ V
) the power supply is consid-
HYST
), where V
DD
(continued)
2 ms
Reduced F
0.5-1.0 MHz
12 ms minimum
/ Brownout Detector
DD
DD
OUT
2 ms
rises and stays
slowly changes
HYST
6 ms
is a small
11
Since the clock is only active for the last 1 or 2ms of the
reset interval, when V
time, energy savings are realized and the start-up of the
whole system is made easier. The commonly used reset
approach forces the processor to turn the oscillator on
and to run at full speed (thus consuming full power) dur-
ing the critical time when the (possibly depleted) battery is
trying to raise V
SH3003 allows the power source to charge the bypass
capacitors and raise the level of V
load. Only when power has stabilized is the target micro
permitted to start expending energy.
When a brownout event occurs, the SH3003 continues to
provide the clock to the target processor, but at a reduced
frequency between 500kHz and 1.0MHz. After a delay of
2ms this clock is stopped, automatically lowering the en-
ergy consumption of the whole system, (see Figure 2).
A Noise Filter (see Figure 1, Page 10) prevents reset ac-
tivations from noise and small power glitches on the V
line. A typical behavior is shown in Figure 3 for the V
level just above V
of the negative-going spikes.
When VDD is falling, both reset lines are guaranteed to
activate within 5μs from the time V
Figure 3. Response to negative voltage spikes
10
5
0
0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5
DD
BO
to an acceptable level. In contrast, the
and various amplitudes and durations
Guaranteed NO reset
DD
has already been valid for some
Am plitude, V
Guaranteed reset
DD
BO
Duration
with little additional
is crossed over.
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SH3003
DD
DD