AB08X5 Real-Time Clock Family
Date of Issue: October 16, 2014
Page 1 of 33
3.0 x 3.0 mm
Abracon Drawing #453567
Revision: C
Features
• Ultra-low supply current (all at 3V):
- 14 nA with RC oscillator
- 22 nA with RC oscillator and Autocalibration
- 55 nA with crystal oscillator
• Baseline timekeeping features:
- 32.768 kHz crystal oscillator with integrated
load capacitor/resistor
- Counters for hundredths, seconds, minutes,
hours, date, month, year, century, and week-
day
- Alarm capability on all counters
- Programmable output clock generation
(32.768 kHz to 1 year)
- Countdown timer with repeat function
- Automatic leap year calculation
• Advanced timekeeping features:
- Integrated power optimized RC oscillator
- Advanced crystal calibration to ± 2 ppm
- Advanced RC calibration to ± 16 ppm
- Automatic calibration of RC oscillator to crystal
oscillator
- Watchdog timer with hardware reset
- 256 bytes of general purpose RAM
• Power management features:
- Automatic switchover to VBAT
- External interrupt monitor
- Programmable low battery detection threshold
- Programmable analog voltage comparator
• I
2
C (up to 400 kHz) and 3-wire or 4-wire SPI (up
to 2 MHz) serial interfaces available
• Operating voltage 1.5-3.6 V
• Clock and RAM retention voltage 1.5-3.6 V
• Operating temperature –40 to 85 °C
• All inputs include Schmitt Triggers
• 3x3 mm QFN-16 package
Applications
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Smart cards
Wireless sensors and tags
Medical electronics
Utility meters
Data loggers
Appliances
Handsets
Consumer electronics
Communications equipment
Description
The ABRACON AB08X5 Real-Time Clock family
provides a groundbreaking combination of ultra-low
power coupled with a highly sophisticated feature
set. With power requirements significantly lower than
any other industry RTC (as low as 14 nA), these are
the first semiconductors based on
innovative
SPOT
TM
(Subthreshold
Power
Optimized
Technology) CMOS platform. The AB08X5 includes
on-chip oscillators to provide minimum power
consumption, full RTC functions including battery
backup and programmable counters and alarms for
timer and watchdog functions, and either an I
2
C or
SPI serial interface for communication with a host
controller.
Disclaimer:
AB08X5 series of devices are
based on innovative SPOT technology,
proprietary to Ambiq Micro.
AB08X5 Real-Time Clock Family
Date of Issue: October 16, 2014
Page 2 of 33
3.0 x 3.0 mm
Abracon Drawing #453567
Revision: C
1.
Family Summary
The AB08X5 family consists of several members (see Table 1). All devices are supplied in a standard 3x3
mm QFN-16 package. Members of the software and pin compatible AB18X5 RTC family are also listed.
Table 1: Family Summary
Baseline
Timekeeping
Part #
XT
Osc
Number
of GP
Outputs
3
2
Advanced Timekeeping
Calib/
Auto-
calib
Power Management
Interface
RC
Osc
Watch-
dog
RAM
(B)
VBAT
Switch
Reset
Mgmt
Ext
Int
Power
Switch and
Sleep FSM
AB0805
AB0815
■
■
■
■
■
■
■
■
256
256
■
■
■
■
I
2
C
SPI
Software and Pin Compatible AB18X5 Family Components
AB1805
AB1815
■
■
4
3
■
■
■
■
■
■
256
256
■
■
■
■
■
■
■
■
I
2
C
SPI
AB08X5 Real-Time Clock Family
Date of Issue: October 16, 2014
Page 3 of 33
3.0 x 3.0 mm
Abracon Drawing #453567
Revision: C
2.
Functional Description
VCC VBAT
100ths
Seconds
Minutes
Hours
Days
Weekdays
Months
Years
Alarms
XT Osc
Divider
Timer
WDT
Control
RC Osc
Divider
RAM
Int/Clock
Figure 1 illustrates the AB08X5 functional design.
nCE
SDI
SCL
SDA/O
I2C/SPI
Interface
Power
Control
Analog
Compare
Calibration Engine
XO
XI
WDI
EXTI
FOUT/nIRQ
nIRQ2
nTIRQ
VSS
Figure 1. Detailed Block Diagram
The AB08X5 serves as a full function RTC for host processors such as microcontrollers. The AB08X5
includes 3 distinct feature groups: 1) baseline timekeeping features, 2) advanced timekeeping features,
and 3) basic power management features. Functions from each feature group may be controlled via I/O
offset 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). Each feature group is described briefly below and
in greater detail in subsequent sections.
The baseline timekeeping feature group supports the standard 32.786 kHz crystal (XT) oscillation mode for
maximum frequency accuracy with an ultra-low current draw of 55 nA. 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.
AB08X5 Real-Time Clock Family
Date of Issue: October 16, 2014
Page 4 of 33
3.0 x 3.0 mm
Abracon Drawing #453567
Revision: C
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 AB08X5 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 AB08X5 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 AB08X5 also
includes digitally-tunable voltage detection on the backup power supply.
AB08X5 Real-Time Clock Family
Date of Issue: October 16, 2014
Page 5 of 33
3.0 x 3.0 mm
Abracon Drawing #453567
Revision: C
3.
AB08X5 Example Applications
3.1 Battery Backed Up RTC
The most common AB08X5 application is a battery backed up RTC, which maintains time and may hold
data in RAM. The AB08X5 is normally powered from a system power supply, which may be a larger
battery. The AB08X5 is continuously charging a supercapacitor or rechargeable battery via the internal
trickle charger. When the main power supply goes away, the AB08X5 automatically switches to the VBAT
supply and maintains time and RAM data at very low battery supply currents.
System Power
1.5k*
VBAT
Battery/
Supercap
XO
XI
VSS
VCC
I2C/SPI
VCC
AB08X5
FOUT/nIRQ
IRQ
VSS
MCU
* Total battery series impedance = 1.5k ohms, which may require an external resistor
3.2 RTC with Interrupt Aggregation
The flexible inputs of the AB08X5 can be used to aggregate a variety of interrupt sources, including
external digital inputs, analog levels, timers and alarms into a single interrupt source to an MCU.
System Power
XO
XI
Digital Inputs
Analog Level
WDI
EXTI
VBAT
VCC
I2C/SPI
VCC
AB08X5
FOUT/nIRQ
IRQ
MCU
VSS
VSS
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