Automatic_power_off_switch

Published:2009/7/24 22:09:00 Author:Jessie | From:SeekIC

Figure 6-42 shows a MAX931 comparator connected as a timed, automatic power-off circuit for a 40-mA supply. The comparator output is the supply output. With a 10-mA load, the circuit provides a voltage of (VBATT-0.12 V), but it draws only 3.5 μA of quiescent current. Using the values shown, the three-resistor voltage divider programs the maximum ±50 mV of hysteresis and sets the IN- voltage at 100 mV. This gives an IN+ trip threshold of about 50 mV for the IN+ falling. The RC time constant determines the maximum power-on time of the OUT pin (8) before power-down occurs. This period (in seconds) can be approximated by: R×C×4.6. For example: 2 M×10 μF×4.6=92 (seconds). MAXIM NEW RELEASES DATA BOOK, 1995, P, 3-57.



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