SS8039 SSC [Silicon Standard Corp.], SS8039 Datasheet - Page 6

• Manufacturer Part Number: SS8039
• Description: Microprocessor Voltage Monitor with Manual Reset
• Manufacturer: SSC [Silicon Standard Corp.]

Rev.2.02 1/06/2004
Applications Information
Negative-Going V
In addition to issuing a reset to the µP during power-up,
power-down, and brownout conditions, the SS8039H
and SS8039L are relatively immune to short-duration
negative -going V
Figure1 shows typical transient durations, vs. the reset
comparator overdrive, for which both the SS8039H and
SS8039L do not generate a reset pulse. The graph was
generated using a negative-going pulse applied to V
starting 0.5V above the actual reset threshold and ending
below it by the magnitude indicated (reset comparator
overdrive). The graph indicates the maximum pulse width
a negative-going V
reset pulse. As the magnitude of the transient increases
(goes farther below the reset threshold), the maximum
allowable pulse width decreases. For the SS8039x463
and SS8039x438, a V
the reset threshold and lasts 15µs or less will not typically
cause a reset pulse. A 0.1µF bypass capacitor mounted
as close as possible to the V
transient immunity.
Ensuring a Valid Reset Output Down to V
When V
longer sinks current—it becomes an open circuit.
Therefore, high-impedance CMOS logic inputs con-
nected to RESET can drift to undetermined voltages.
This presents no problem in most applications since
most µP and other circuitry is inoperative with
1V. However, in applications where RESET must be
valid down to 0V, adding a pull-down resistor to RESET
causes any stray leakage currents to flow to ground,
holding RESET low (Figure 2). R1’s value is not critical;
100k
enough to pull RESET to ground.
CC
is large enough not to load RESET and small
falls below 1V, the SS8039 RESET output no
CC
CC
CC
transients (glitches).
transient can have without causing a
Transients
CC
transient that goes 100mV below
CC
pin provides additional
www.SiliconStandard.com
CC
VCC
= 0
below
CC
,
Benefits of Highly Accurate Reset Threshold
Most µP supervisor ICs have reset threshold voltages
between 5% and 10% below the value of nominal supply
voltages. This ensures a reset will not occur within 5% of
the nominal supply, but will occur when the supply is
10% below nominal.
When using ICs rated at only the nominal supply ±5%,
this leaves a zone of uncertainty where the supply is
between 5% and 10% low, and where the reset may or
may not be asserted.
The SS8039x uses highly accurate circuitry to ensure that
reset is asserted close to the 5% limit, and long before the
supply has declined to 10% below nominal.
SS8039
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