AB08XX Series
Real Time Clock Module
Date of Issue: Sept. 10
th
, 2012
Page (2) of (12)
3.0 x 3.0 mm
Abracon Drawing #
ESD Sensitive
Revision #: Initial Release
2. AB08XX Functional Description
VCC VBAT
100ths
Seconds
Minutes
Hours
Days
Weekdays
Months
Years
Alarms
Timer
WDT
Control
RC Osc
Divider
RAM
nCE
SDI
SCL
SDA/O
Power
Control
I2C/SPI
Interface
Analog
Compare
Calibration Engine
XO
XT Osc
Divider
XI
WDI
EXTI
Int/Clock
FOUT/nIRQ
nIRQ2
nTIRQ
CLKOUT/nIRQ3
VSS
The AB08XX serves as a full function RTC for host processors such as microcontrollers. The AB08XX includes 3 distinct
feature groups: 1) baseline timekeeping features and 2) advanced timekeeping features, and 3) basic power management
features. Functions from each feature group may be controlled via memory mapped registers. These registers are accessed
using either an I
2
C serial interface (e.g., in the AB0805) or a SPI serial interface (e.g., in the AB0815).
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 AB08XX 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.
Power management features built into the AB08XX 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
digitally-selectable threshold and switches to backup power (VBAT). Up to 256B of ultra-low leakage RAM enable the
storage of key parameters when operating on backup power. The AB08XX also includes digitally-tunable voltage
monitoring for brown-out detection and power-on reset.
ABRACON [ ABRACON CORPORATION ]
