DS1233 5V EconoReset www.maxim-ic.com FEATURES PIN ASSIGNMENT Automatically restarts microprocessor after power failure DALLAS DS1233 Monitors pushbutton for external override Econo Reset Internal circuitry debounces pushbutton switch Maintains reset for 350ms after V returns to CC an in-tolerance condition or pushbutton released 1 Accurate 5%, 10%, or 15% microprocessor 1 2 3 5V power supply monitoring Reduces need for discrete components 1 2 3 Precision temperature-compensated voltage 2 4 3 reference and voltage sensor BOTTOM VIEW TOP VIEW Low-cost TO-92 package or surface-mount TO-92 PACKAGE SOT-223 PACKAGE See Mech. See Mech. SOT-223 package Drawings Section Drawings Section Internal 5k pull-up resistor on Website on Website Operating temperature of -40 C to +85 C PIN DESCRIPTION PIN 1 GROUND PIN 2 RESET PIN 3 V CC PIN 4 GROUND (SOT-223 ONLY) DESCRIPTION The DS1233 EconoReset monitors two vital conditions for a microprocessor: power supply and external override. A precision temperature-compensated reference and comparator circuit are used to monitor the status of the power supply (V ). When an out-of-tolerance condition is detected, an internal power-fail CC signal is generated which forces reset to the active state. When V returns to an in-tolerance condition, CC the reset signal is kept in the active state for approximately 350ms to allow the power supply and processor to stabilize. The second function of the DS1233 is pushbutton reset control. The DS1233 debounces a pushbutton closure and will generate a 350ms reset pulse upon release. OPERATION POWER MONITOR The DS1233 provides the functions of detecting out-of-tolerance power supply conditions and warning a processor-based system of impending power failure. When V is detected as out-of-tolerance, as CC RST signal is asserted. On power-up, RST is kept active defined by the tolerance of the part selected, the for approximately 350ms after the power supply has reached the selected tolerance. This allows the power supply and microprocessor to stabilize before RST is released. 1 of 5 122001DS1233 OPERATION PUSHBUTTON RESET The DS1233 provides for a pushbutton switch to be connected to the RST output pin. When the DS1233 is not in a reset cycle, it continuously monitors the RST signal for a low going edge. If an edge is detected, the DS1233 will debounce the switch by pulling the RST line low. After the internal timer has expired, the DS1233 will continue to monitor the RST line. If the line is still low, the DS1233 will continue to monitor the line looking for a rising edge. Upon detecting a release, the DS1233 will force the RST line low and hold it low for 350ms. NOTE: For proper operation with an external pushbutton, a capacitor between 100pF and 0.01 F must be connected between RST and ground. In applications where additional reset current is required, a minimum capacitance of 500pF should be used, along with a parallel external pull-up resistor of 1k minimum. BLOCK DIAGRAM Figure 1 APPLICATION EXAMPLE Figure 2 2 of 5