lm3722im5x-4.63 National Semiconductor Corporation, lm3722im5x-4.63 Datasheet - Page 7

• Manufacturer Part Number: lm3722im5x-4.63
• Description: 5-pin Microprocessor Reset Circuits
• Manufacturer: National Semiconductor Corporation

Timing Diagram
Circuit Information
RESET OUTPUT
The reset input of a µP initializes the device into a known
state. The LM3722/LM3723/LM3724 microprocessor voltage
monitoring circuits assert a forced reset output to prevent
code execution errors during power-up, power-down, and
brownout conditions.
RESET is guaranteed valid for V
the reset threshold, an internal timer maintains the output for
the reset timeout period. After this interval, reset goes high
and the microprocessor initializes itself into a known state.
The LM3722 and LM3724 offer an active-low RESET; the
LM3723 offers an active-high RESET.
As V
brownout), the reset activates (see the Negative-Going V
Transients section). When V
threshold, the internal timer starts. Reset holds until V
ceeds the reset threshold for longer than the reset timeout
period. After this time, reset releases.
Additionally, the Manual Reset input (MR) will initiate a forced
reset. See the Manual Reset Input section.
The LM3722/LM3723/LM3724 reset outputs ignore short du-
ration glitches on V
tion section for details.
RESET THRESHOLD
The LM3722/LM3723/LM3724 are available with reset volt-
ages of 4.63V, 3.08V, and 2.32V which are suitable for mon-
CC
drops below the reset threshold (such as during a
CC
and MR. See the Applications Informa-
CC
again rises above the reset
CC
≥
1V. Once V
CC
exceeds
CC
ex-
CC
7
itoring 5.0V, 3.3V, and 2.5V supplies respectively. Other reset
thresholds in the 2.20V to 5.0V range, in 10 mV steps, are
available; contact National Semiconductor for details.
MANUAL RESET INPUT (MR)
Many µP-based products require a manual reset capability,
allowing the operator to initiate a reset. The MR input is fully
debounced and provides an internal 22 kΩ pull-up. When the
MR input is pulled below V
reset is asserted after a typical delay of 2 µs. Reset remains
active as long as MR is held low, and releases after MR rises
above V
digital logic to assert reset or to daisy chain supervisory cir-
cuits.
Applications Information
BENEFITS OF PRECISION RESET THRESHOLDS
A microprocessor supply supervisor must provide a reset out-
put within a predictable range of the supply voltage. A com-
mon threshold range is between 5% and 10% below the
nominal supply voltage. The 4.63V, 3.08V and 2.32V options
of the LM3722/LM3723/LM3724 use highly accurate circuitry
to ensure that the reset threshold occurs only within this range
(for 5.0V, 3.3V and 2.5V supplies). Table 1 shows how the
standard reset thresholds apply to 5.0V, 3.3V, and 2.5V nom-
inal supply voltages.
IH
and the reset timeout period expires. Use MR with
IL
(0.25V
CC
) for more than 100 ns,
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