DS1233A 3.3V EconoReset www.maxim-ic.com FEATURES PIN ASSIGNMENT Automatically restarts microprocessor after power failure DALLAS DS1233A 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 10% or 15% microprocessor 3.3V 1 2 3 power supply monitoring Reduces need for discrete components 1 2 3 Precision temperature-compensated voltage 2 3 4 reference and voltage sensor BOTTOM VIEW TOP VIEW Low-cost TO-92 package or surface mount TO-92 PACKAGE SOT-223 PACKAGE SOT-223 package Internal 5kpull-up resistor Operating temperature of -40C to +85 C PIN DESCRIPTION PIN 1 GROUND PIN 2 RESET PIN 3 V CC PIN 4 GROUND (SOT-223 ONLY) DESCRIPTION The DS1233A 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 DS1233A is pushbutton reset control. The DS1233A debounces a pushbutton closure and will generate a 350ms reset pulse upon release. OPERATION POWER MONITOR The DS1233A 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 defined by the tolerance of the part selected, the RST signal is asserted. On power-up, RST is kept active 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 122001 DS1233A OPERATION PUSHBUTTON RESET The DS1233A provides for a pushbutton switch to be connected to the RST output pin. When the DS1233A is not in a reset cycle, it continuously monitors the RST signal for a low-going edge. If an edge is detected, the DS1233A will debounce the switch by pulling the RST line low. After the internal timer has expired, the DS1233A will continue to monitor the RST line. If the line is still low, the DS1233A will continue to monitor the line looking for a rising edge. Upon detecting a release, the DS1233A 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 0.01F must be connected between RST and ground. In applications where additional reset current is required, a minimum capacitance of 500 pF 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