AB18X5 Real-Time Clock with Power

Management Family

Date of Issue: October 16, 2014

3.0 x 3.0 mm

Page 4 of 37

Abracon Drawing #453568

Revision: C

complement of countdown timers and alarms may additionally be set to initiate interrupts or resets on

several of the outputs.

The advanced timekeeping feature group supports two additional oscillation modes: 1) RC oscillator mode,

and 2) Autocalibration mode. At only 14 nA, the temperature-compensated RC oscillator mode provides an

even lower current draw than the XT oscillator for applications with reduced frequency accuracy

requirements. A proprietary calibration algorithm allows the AB18X5 to digitally tune the RC oscillator

frequency and the XT oscillator frequency with accuracy as low as 2 ppm at a given temperature. In

Autocalibration mode, the RC oscillator is used as the primary oscillation source and is periodically

calibrated against the XT oscillator. Autocalibration may be done automatically every 8.5 minutes or 17

minutes and may also be initiated via software. This mode enables average current draw of only 22 nA

with frequency accuracy similar to the XT oscillator. The advanced timekeeping feature group also

includes a rich set of input and output configuration options that enables the monitoring of external

interrupts (e.g., pushbutton signals), the generation of clock outputs, and watchdog timer functionality.

Power management features built into the AB18X5 enable it to operate as a backup device in both line-

powered and battery-powered systems. An integrated power control module automatically detects when

main power (VCC) falls below a threshold and switches to backup power (VBAT). 256B of ultra-low

leakage RAM enable the storage of key parameters when operating on backup power.

The AB18X5 is the first RTC to incorporate a number of more advanced power management features. In

particular, the AB18X5 includes a finite state machine (integrated with the Power Control block in Figure 1)

that can control a host processor as it transitions between sleep/reset states and active states. Digital

outputs can be configured to control the reset signal or interrupt input of the host controller. The AB18X5

additionally integrates a power switch with ~1 Ω impedance that can be used to cut off ground current on

the host microcontroller and reduce sleep current to <1 nA. The AB18X5 parts can wake up a sleeping

system using internally generated timing interrupts or externally generated interrupts generated by digital

inputs (e.g., using a pushbutton) or an analog comparator. The aforementioned functionality enables users

to seamlessly power down host processors, leaving only the energy-efficient AB18X5 chip awake. The

AB18X5 also includes voltage detection on the backup power supply.