Table of Contents
Advertisement
2.1 Low V
Reset
DD
The SH3000 drives the reset pins active whenever V
threshold. V
can be set using bits 0:5 of the V
BO
from 2.30 V to 4.40 V in average increments of 33.33 mV–see Table 2.
The default V
value is loaded on power-up from the factory-programmed OTP nonvolatile memory. It
BO
can be re-programmed at any time or it can be permanently protected from any changes by setting the
V
lock flag or an OTP write-protect flag.
BO
On power up, both the active high and active low reset pins are driven active. These outputs are typically
valid for a V
level of at least 0.5 V, and guaranteed to be valid for a V
DD
The reset output pins remain active until V
V
is a small fixed amount of hysteresis, nominally 50 mV. This hysteresis is added to prevent false
HYST
triggering from noise or small power glitches.
At the threshold level (V
BO
lines become inactive 3–5 ms after power is valid. In the case of brownout, the reset is released after a
delay of 6 ms, but no less than 12 ms from the moment brownout has been detected.
Such a fast reset is possible because the SH3000 provides a fast-starting clock that is free of crystal start-
up time delays. This gives the SH3000 an advantage over other external reset circuits, which must have a
long reset pulse duration to accommodate long and unpredictable crystal start-up times.
The SH3000 guarantees that before the reset signals are inactive a valid and stable clock is available for
at least 1 ms on power up, or 2 ms after brownout, so that internal synchronous reset and initialization of
the host microcontroller can proceed normally.
With the clock becoming active 1-2 ms before the reset lines become inactive, considerable energy is
conserved since the clock is not active during the whole reset period.
SH3000UM version 0.95
Copyright ©2002 Semtech Corporation
BO
Table 2: Programmable V
4.400 4.367 4.333 4.300 4.267 4.233 4.200 4.167
4.133 4.100 4.067 4.033 4.000 3.967 3.933 3.900
3.867 3.833 3.800 3.767 3.733 3.700 3.667 3.633
3.600 3.567 3.533 3.500 3.467 3.433 3.400 3.367
3.333 3.300 3.267 3.233 3.200 3.167 3.133 3.100
3.067 3.033 3.000 2.967 2.933 2.900 2.867 2.833
2.800 2.767 2.733 2.700 2.667 2.633 2.600 2.567
2.533 2.500 2.467 2.433 2.400 2.367 2.333 2.300
rises and stays above the level of V
DD
+ V
), the power supply is considered valid. On initial power up, the reset
HYST
2002-08
is below the value of V
DD
Value register (R0x10). V
Values (Volts)
BO
level of 1.0 V.
DD
SH3000 User Manual
Preliminary
, the brownout reset
BO
can be set to a value
BO
+ V
, where
BO
HYST
5
Advertisement
Table of Contents
