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Maxim > Design Support > Technical Documents > Application Notes > Amplifier and Comparator Circuits > APP 1186
Keywords: microprocessor reset generator, ultra-low power, relaxation oscillator, long battery life, pulse
generator
APPLICATION NOTE 1186
Ultra Low Power Reset Generator
By: Philip Simpson, Applications Director
Sep 06, 2002
Abstract: This application note describes an ultra-low power microprocessor reset generator that is
capable of operating for decades from a single AA Lithium cell. Where continuous intermittent reset is
desired, this relaxation-oscillator circuit can provide adjustable pulse width and reset period. Typical
operation producing 100µs pulses each second requires only 1µA current from a 1.8-5.5V supply.
Formulas are provided for calculation of component values for a wide range of pulse width and period.
When a processor-controlled device must be guaranteed to operate, designers often choose to reset the
processor periodically rather than rely on a watchdog circuit. In low-power systems the periodic reset
generator can consume a large part of the system current budget or may not be guaranteed to operate
at low voltages.
This application note describes a low-power reset generator that generates a low going reset pulse of
100µS duration once per second, consumes less than 1µA and will operate from 1.8V to 5V with only
slight variation of the output period.
Figure 1. This reset circuit consumes less than 1µA and delivers a 100-µsec-wide reset pulse every 1.3
sec.
The circuit is an adaptation of a normal relaxation oscillator with a differentiator and diode clamp on the
output to generate the 100µS low going pulse. The pulse width can be adjusted by varying C
p
or R
p
and
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