AB18XX Series

Real Time Clock Module

Date of Issue: Sept. 10

3.0 x 3.0 mm

ESD Sensitive

Page (2) of (13)

Abracon Drawing #

Revision #: Initial Release

2.

AB18XX Functional Description

XT Osc

RC Osc

Divider

Seconds

Minutes

Hours

Days

Weekdays

Months

Years

Power

Control

VCC VBAT

I2C/SPI

Interface

SCL

SDA/O

Control

Alarms

Int/Clock

FOUT/nIRQ

PSW/nIRQ2

VSS

CLKOUT/nIRQ3

SDI

nCE

WDI

Reset

nEXTR

nRST

RAM

XO

XI

nTIRQ

Timer

WDT

100ths

Divider

Calibration Engine

EXTI

Analog

Compare

The AB18XX serves as a companion part for host processors including microcontrollers, radios, and digital signal

processors. It tracks time as in a typical RTC product and additionally provides unique power management functionality that

makes it ideal for highly energy-constrained applications. To support such operation, the AB18XX includes 3 distinct feature

groups: 1) baseline timekeeping features, 2) advanced timekeeping features, and 3) power management features. Functions

from each feature group may be controlled via memory mapped registers. These registers are accessed using either an I

serial interface (e.g., in the AB1805) or a SPI serial interface (e.g., in the AB1815). Each feature group is described briefly

below.

The baseline timekeeping feature group supports the standard 32 kHz crystal (XT) oscillation mode for maximum frequency

accuracy with an ultra-low current draw of 55 nA. An extended calibration mode enables low jitter digital calibration to an

accuracy of ±2 ppm over a range of -614 ppm to +244 ppm. The baseline timekeeping feature group also includes a standard

set of counters monitoring hundredths of a second up through centuries. A 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) auto-

calibration mode. At only 15 nA, the temperature-compensated ±10% 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 AB18XX to digitally tune the RC oscillator frequency with accuracy as low as ±2 ppm at a given

temperature and very low calibration jitter. In autocalibration mode, the RC oscillator is used as the primary oscillation

source and is periodically calibrated against the XT oscillator. Autocalibration may be executed every autocalibration period

(ACP) of 8.5 minutes or 17 minutes and may also be initiated via software. This mode enables average current draw of only

20 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.