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ADM707 Datasheet(PDF) 10 Page - Analog Devices |
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ADM707 Datasheet(HTML) 10 Page - Analog Devices |
10 / 12 page ADM705/ADM706/ADM707/ADM708 Rev. G | Page 10 of 12 APPLICATIONS INFORMATION A typical application circuit is shown in Figure 18. The unregulated dc input supply is monitored using PFI via the resistive divider network. Resistor R1 and Resistor R2 should be selected so that when the supply voltage drops below the desired level (such as 8 V), the voltage on PFI drops below the 1.25 V threshold, thereby generating an interrupt to the microprocessor. Monitoring the preregulator input provides additional time to execute an orderly shutdown procedure before power is lost. 7V TO 15V INPUT POWER MICROPROCESSOR 5V VCC R1 R2 1.25V PFI PFO ADP3367 – + RESET ADM705/ADM706/ ADM707/ADM708 Figure 18. Typical Application Circuit Microprocessor activity is monitored using WDI. This is driven using an output line from the processor. The software routines should toggle this line at least once every 1.60 seconds. If a problem occurs and this line is not toggled, WDO goes low and a nonmaskable interrupt is generated. This interrupt routine can be used to clear the problem. If, in the event of inactivity on the WDI line, a system reset is required, WDO should be connected to MR, as shown in Figure 19. ADM705/ ADM706 RESET GND I/O LINE MICROPROCESSOR MR WDI WDO RESET Figure 19. RESET From WDO MONITORING ADDITIONAL SUPPLY LEVELS It is possible to use the power-fail comparator to monitor a second supply as shown in Figure 20. The two sensing resistors, R1 and R2, are selected so that the voltage on PFI drops below 1.25 V at the minimum acceptable input supply. PFO can be connected to MR so that a reset is generated when the supply drops out of tolerance. In this case, if either supply drops out of tolerance, a reset is generated. ADM705/ ADM706 RESET GND MR PFI PFO RESET VCC R1 R2 VX 5V MICROPROCESSOR Figure 20. Monitoring 5 V and an Additional Supply, VX MICROPROCESSOR WITH BIDIRECTIONAL RESET To prevent contention for microprocessors with a bidirectional reset line, a current limiting resistor should be inserted between the ADM70x RESET output pin and the microprocessor RESET pin. This limits the current to a safe level if there are conflicting output reset levels. A suitable resistor value is 4.7 kΩ. If the reset output is required for other uses, it should be buffered, as shown in Figure 21. ADM70x RESET GND RESET GND BUFFERED RESET 5V VCC MICROPROCESSOR Figure 21. Bidirectional Input/Output RESET |
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