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2011-05-05 12:39:07
Abstract: Impact or vibration can cause momentary interruptions when batteries lose contact. To ensure continuity of power in battery-powered systems, add this three-IC circuit.
When you drop a battery-powered device, the impact can open internal contacts for as long as 10ms, producing a momentary loss of power that can cause a false low-battery indication. (There is sometimes a similar momentary effect on the device's owner, especially if the device is expensive, but that's beyond the scope of this application note).
You can insure continuity of power by adding a large capacitor across the battery. The capacitor must provide a certain amount of voltage headroom as margin against the discharge of load current. The capacitor voltage varies with discharge current as dV = Idt/C, so insufficient headroom calls for an even larger capacitor.
Another problem is that large capacitors tend to be leaky. Capacitor leakage is usually not a problem during normal oper
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ged without storing the configuration in the nonvolatile memory. This allows the system controller to overwrite the current configuration and try it without disrupting the power-on default state. Hence the system controller can try the new software version and if it fails, upon system power-up, the nonvolatile I/O expanders will retain the old configuration and revert to the older stable software version. When the system controller is sure that it wants to always operate with the newly loaded software, it writes the configuration into nonvolatile memory which will make it the default power-up value. The SEE bit in the DS4510, DS4520, and DS4550 nonvolatile I/O expanders controls this feature. Please see their respective data sheets for more information on the operation of the SEE bit.
Figure 1. Using nonvolatile I/O expanders to select flash memory.
