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ADM705 Datasheet(PDF) 9 Page - Analog Devices |
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ADM705 Datasheet(HTML) 9 Page - Analog Devices |
9 / 12 page ADM705/ADM706/ADM707/ADM708 Rev. G | Page 9 of 12 Adding Hysteresis to the Power-Fail Comparator For increased noise immunity, hysteresis can be added to the power-fail comparator. Because the comparator circuit is noninverting, hysteresis can be added simply by connecting a resistor between the PFO output and the PFI input, as shown in . Figure 16 7V TO 15V INPUT POWER TO MICROPROCESSOR NMI R3 5V VCC R1 R2 1.25V PFI PFO ADP3367 5V 0V 0V VL VIN VH – + PFO ADM705/ADM706/ ADM707/ADM708 Figure 16. Adding Hysteresis to the Power-Fail Comparator When PFO is low, Resistor R3 sinks current from the summing junction at the PFI pin. When PFO is high, Resistor R3 sources current into the PFI summing junction. This results in differing trip levels for the comparator. Further noise immunity can be achieved by connecting a capacitor between PFI and GND. The equations used to calculate the hysteresis are as follows: ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ + = ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ − − + = ⎥⎦ ⎤ ⎢⎣ ⎡ ⎟ ⎠ ⎞ ⎜ ⎝ ⎛ × + + = R2 R2 R1 V R3 V R2 R1 V R1 R3 R2 R3 R2 V MID CC L H 25 . 1 25 . 1 25 . 1 25 . 1 1 25 . 1 VALID RESET BELOW 1 V VCC The ADM705/ADM706/ADM707/ADM708 are guaranteed to provide a valid reset level with VCC as low as 1 V (see the Typical Performance Characteristics section). As VCC drops below 1 V, the internal transistor does not have sufficient drive to hold the voltage RESET at 0 V. A pull-down resistor can be connected externally, as shown in , to hold the line low if required. Figure 17 ADM705/ADM706/ ADM707/ADM708 GND RESET R1 Figure 17. RESET Valid Below 1 V |
Similar Part No. - ADM705_15 |
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Similar Description - ADM705_15 |
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