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MAX804RMJA Datasheet(PDF) 7 Page - Maxim Integrated Products |
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MAX804RMJA Datasheet(HTML) 7 Page - Maxim Integrated Products |
7 / 12 page Watchdog Input (MAX690_/802_/804_/805_) The watchdog circuit monitors the µP’s activity. If the µP does not toggle the watchdog input (WDI) within 1.6sec, a reset pulse is triggered. The internal 1.6sec timer is cleared by either a reset pulse or by a transition (low-to- high or high-to-low) at WDI. If WDI is tied high or low, a – R — E — S — E — T – pulse is triggered every 1.8sec (tWD plus tRS). As long as reset is asserted, the timer remains cleared and does not count. As soon as reset is deasserted, the timer starts counting. Unlike the 5V MAX690 family, the watchdog function cannot be disabled. Power-Fail Comparator The PFI input is compared to an internal reference. If PFI is less than VPFT, – P — F — O – goes low. The power-fail comparator is intended for use as an undervoltage detector to signal a failing power supply. However, the comparator does not need to be dedicated to this function because it is completely separate from the rest of the circuitry. The power-fail comparator turns off and – P — F — O – goes low when VCC falls below VSW on power-down. The power- fail comparator turns on as VCC crosses VSW on power-up. If the comparator is not used, connect PFI to ground and leave – P — F — O – unconnected. – P — F — O – may be connected to – M — R – on the MAX704_/MAX806_ so that a low voltage on PFI will generate a reset (Figure 5b). 3.0V/3.3V Microprocessor Supervisory Circuits _______________________________________________________________________________________ 7 V BATT RESET (RESET) WDI VCC MR BATTERY SWITCHOVER COMPARATOR RESET COMPARATOR RESET GENERATOR WATCHDOG TIMER BATTERY SWITCHOVER CIRCUITRY MAX690T/S/R MAX704T/S/R MAX802T/S/R MAX804T/S/R MAX805T/S/R MAX806T/S/R PFO VOUT PFI VPFT 1.237V 1.237V ** * * POWER-FAIL COMPARATOR * MAX690T/S/R, MAX802T/S/R, MAX804T/S/R, MAX805T/S/R ONLY ** MAX704T/S/R, MAX806T/S/R ONLY ( ) MAX804T/S/R, MAX805T/S/R ONLY VBATT = 3.6V 3.0V OR 3.3V VSW tWP RESET PFO VCC ( ) MAX804T/S/R, MAX805T/S/R ONLY, RESET EXTERNALLY PULLED UP TO VCC VOUT VSW (RESET) 3.0V OR 3.3V 3.0V OR 3.3V 0V VRST V BATT = PFI = 3.6V IOUT = 0mA Figure 1. Block Diagram Figure 2. Timing Diagram |
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