AB18X5 Real-Time Clock with Power

Management Family

Date of Issue: October 16, 2014

3.0 x 3.0 mm

Page 5 of 37

Abracon Drawing #453568

Revision: C

3. AB18X5 Application Examples

The AB18X5 enables a variety of system implementations in which the AB18X5 can control power usage

by other elements in the system. This is typically used when the entire system is powered from a battery

and minimizing total power usage is critical. The backup RAM in the AB18X5 can be used to hold key

MCU parameters when it is powered down.

3.1 VSS Power Switched

In the recommended implementation, the internal power switch of the AB18X5 is used to completely turn

off the MCU and/or other system elements. In this case the PSW/nIRQ2 output is configured to generate

the Sleep function. Under normal circumstances, the PSW/nIRQ2pin is pulled to VSS with less than 1 ohm

of resistance, so that the MCU receives full power. The MCU initiates a SLP operation, and when the

AB18X5 enters Sleep Mode the PSW/nIRQ2 pin is opened and power is completely removed from the

MCU. This results in significant additional power savings relative to the other alternatives. A variety of

interrupts, including alarms, timers and external interrupts created by a pushbutton as shown, may be used

to exit Sleep Mode and restore MCU power. The RAM of the AB18X5 may be used to retain critical MCU

parameters.

3.2 VCC Power Switched

An external transistor switch T may also be used to turn off power to the MCU. This implementation allows

switching higher current and maintains a common ground. R can be on the order of megohms, so that

negligible current is drawn when the circuit is active and PSW/nIRQ2 is low.

VCC

VSS

IRQ

VCC

AB18X5

MCU

I2C/SPI

VSS

XO

XI

EXTI

FOUT/nIRQ

R

PSW/nIRQ2

VCC

VSS

IRQ

VCC

AB18X5

MCU

I2C/SPI

VSS

R

T

PSW/nIRQ2

FOUT/nIRQ