System_voltage_monitor

Published:2009/7/25 4:26:00 Author:Jessie | From:SeekIC

Figure 8-129 shows a MAX8214 voltage monitor connected to monitor the condition of a six-cell NiCad stack and a lithium backup battery. Larger portable systems often require several voltage-monitoring comparators to detect the status of main and backup batteries, as well as for power-fail monitoring and ac adapter detection. This circuit performs such monitoring and draws only 3 μA per comparator. The input-voltage range for the monitored voltage is 1.25 V to 100 V, and 2.7 V to 11 V for the IC. Quiescent current (VIN = 5 V) is 16 μA, and threshold accuracy is 11% maximum. When the NiCad stack is fully charged, output 3 goes high. When the NiCad stack voltage drops to a low (but still usable) level, output 2 goes low. When the NiCad stack is dead, output 1 goes low. Output 4 goes low when the lithium battery is dead. MAXIM BATTERY MANAGEMENT CIRCUIT COLLECTION, 1994, P. 77.



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