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| DS1233A 3.3V EconoReset www.maxim-ic.com FEATURES Automatically restarts microprocessor after power failure Monitors pushbutton for external override Internal circuitry debounces pushbutton switch Maintains reset for 350ms after VCC returns to an in-tolerance condition or pushbutton released Accurate 10% or 15% microprocessor 3.3V power supply monitoring Reduces need for discrete components Precision temperature-compensated voltage reference and voltage sensor Low-cost TO-92 package or surface mount SOT-223 package Internal 5kW pull-up resistor Operating temperature of -40C to +85C PIN ASSIGNMENT DALLAS DS1233A Econo Reset 1 123 123 BOTTOM VIEW TO-92 PACKAGE See Mech. Drawings Section on Website 243 TOP VIEW SOT-223 PACKAGE See Mech. Drawings Section on Website PIN DESCRIPTION PIN 1 PIN 2 PIN 3 PIN 4 GROUND RESET VCC 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 (VCC). When an out-of-tolerance condition is detected, an internal power fail signal is generated which forces reset to the active state. When VCC returns to an in-tolerance condition, 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 VCC is detected as out-of-tolerance as 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 0.01mF 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 1kW minimum. BLOCK DIAGRAM Figure 1 APPLICATION EXAMPLE Figure 2 2 of 5 DS1233A PUSHBUTTON RESET Figure 3 POWER-UP Figure 4 POWER-DOWN Figure 5 3 of 5 DS1233A ABSOLUTE MAXIMUM RATINGS* Voltage on VCC Pin Relative to Ground Voltage on I/O Relative to Ground Operating Temperature Range Storage Temperature Range Soldering Temperature * -0.5V to +7.0V -0.5V to VCC +0.5V -40C to +85C -55C to +125C 260C for 10 seconds This is a stress rating only and functional operation of the device at these or any other conditions above those indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. RECOMMENDED DC OPERATING CONDITIONS PARAMETER Supply Voltage SYMBOL VCC MIN 1.2 TYP 3.3 MAX 5.5 (-40C to +85C) UNITS V NOTES 1 DC ELECTRICAL CHARACTERISTICS PARAMETER Low Level @ RST Output Current @ 0.4V Operating Current VCC Trip Point 10% VCC Trip Point 15% Output Capacitance Pushbutton Detect Pushbutton Release Internal Pull-Up Resistor SYMBOL VOL IOL ICC VCCTP1 VCCTP2 COUT PBDV PBRD RP (-40C to +85C; VDD = 3.3V 10%) MIN +8 50 2.80 2.64 0.8 0.3 3.75 5 2.88 2.72 2.97 2.80 10 2.0 0.8 6.25 TYP MAX 0.4 UNITS V mA mA V V pF V V kW 1 1, 2 1 1 NOTES 1 AC ELECTRICAL CHARACTERISTICS PARAMETER Reset Active Time VCC Detect to RST VCC Slew Rate (2.85V - 2.3V) VCC Slew Rate (2.3V - 2.85V) Pushbutton Debounce VCC Detect to RST SYMBOL tRST tRPD tF tR PBDB tRPU (-40C to +85C; VCC = 3.3V 10%) MIN 250 300 0 250 250 350 350 450 450 TYP 350 MAX 450 100 UNITS ms ns ms ns ms ms NOTES NOTES: 1) All voltages are referenced to ground. 2) With a 100pF to 0.01mF capacitor connected from RST to ground. 4 of 5 DS1233A ECONORESET SELECTION GUIDE VCC TRIP POINT MIN DS1233-15 DS1233-10 DS1233-5 DS1233D-15 5V DS1233D-10 DS1233D-5 DS1833-15 DS1833-10 DS1833-5 3.3V DS1233A-15 DS1233A-10 4.0 4.25 4.5 4.0 4.25 4.5 4.0 4.25 4.5 2.64 2.8 TYP 4.125 4.375 4.625 4.125 4.375 4.625 4.125 4.375 4.625 2.72 2.88 MAX 4.24 4.49 4.75 4.24 4.49 4.75 4.24 4.49 4.75 2.80 2.97 PUSHBUTTON DETECT MIN 1.8 1.8 1.8 N/A N/A N/A N/A N/A N/A 0.8 0.8 TYP MAX 3.3 3.3 3.3 N/A N/A N/A N/A N/A N/A 2.0 2.0 5 of 5 |
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