CAT871 Datasheet, PDF (7/9 Pages) ON Semiconductor – Dual Input Reset Generator

CAT871, CAT872
APPLICATION INFORMATION
Reset Pulse Operation
When both MR1 and MR2 inputs are kept low, a single
reset pulse is generated after the delay t_{LOW_DELAY}. Even
with both MR1 and MR2 maintained low continuously after
that time, no second reset pulse will be generated. The delay
timer restarts if either MR1 or MR2 (or both) input
transitions from high to low, as shown in the timing diagram
in Figure 13.
System with Two Different Power Supply Voltages
The reset generator can be used in a system where the
supply VDD is different than the MR1, MR2 input logic.
Figure 14 shows an application schematic where the
microcontroller uses a supply VBAT (3.6 V) that is higher
than the VDD rail (1.8 V). MR1 and MR2 inputs are
activated here by two separate switches connected to GND
and pulling the inputs low when pressed. The Schottky diode
provides the supply isolation needed between the
CAT871/CAT872 (VDD) and the microcontroller (VBAT).
Operation with Low VDD Voltage and Brownout
Condition
The CAT871, CAT872 reset generators require a
minimum supply voltage VDD of 1.65 V to guarantee the
normal operation within the specification. To prevent small
VDD supply glitch, a small ceramic capacitor can be added
between the VDD pin and GND.
Figure 13. Reset Timing Diagram
Figure 14. Application Schematic in Dual Supply System
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