AN-1059: Extend Battery Life by Reducing System Power using the EnerChip RTC

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Doc AN-72-1059 Rev A

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Figure 1: Switched Ground Configuration.

Example System Configurations

The system can be configured to cut power to the sensors and microcontroller as shown in Figure 1 and Figure

2. The additional FET in Figure 2 allows the VCC bus to be switched instead of VSS. The PSW/nIRQ2 output

includes a selectable 1Ω FET switch that greatly reduces drops in the switched bus.

Figure 2: Switched VCC Configuration.

Figure 3: Interrupt-Only Configuration.

It is also possible to not switch the power bus, but instead put the microcontroller in deep sleep, and wake

it periodically with an interrupt as shown in Figure 3. This works well with microcontrollers that have higher

internal sleep timer currents but very low current when clocks are disabled and only some memory is retained.

Design Technique:

Firmware must be designed to avoid large memory re-initialization routines on startup

either from reset or from the interrupt.

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