1
st
Edition
ACCURATE
MEMS
REAL-TIME
CLOCKS
Product Guide
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Accurate MEMS Real-Time Clocks Product Guide
www.maximintegrated.com
Table of Contents
3
Introduction
4 Accurate MEMS RTCs at a Glance
6 Benefits of MEMS Technology in RTC Applications
7 Automotive
8 Video Security and Surveillance
9 Industrial and Medical
10 Power Meters
11
Evaluate MEMS RTC Technology with DS323x
Reference and Development Kits
2
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Accurate MEMS Real-Time Clocks Product Guide
Introduction
Advancing Timekeeping Accuracy
In 1999, Maxim Integrated introduced the
DS32kHz,
a 32.768kHz temperature-compensated crystal
oscillator (TCXO), which was the industry's first accurate timekeeping product for real-time clock
(RTC) applications. The product boasted an accuracy of ±7.5ppm across the entire -40°C to +85°C
industrial temperature range.
By 2005, with the combination of innovative packaging technology and improved temperature sensor
capability, we introduced what would be considered the industry’s most accurate RTC, the
DS3231S,
an extremely accurate I²C-integrated RTC/TCXO/crystal. The DS3231S featured a highly reliable and
innovative package that incorporated a 32kHz tuning fork crystal into a standard 16-pin, 300-mil SO.
This highly integrated device further enhanced timekeeping accuracy by providing a frequency accuracy
of less than ±3.5ppm over the -40°C to +85°C temperature range. This accuracy is equivalent to less
than ±0.3 seconds/day.
In 2009, Maxim Integrated embarked on a goal to create a quantum leap in technology advancement
by developing an RTC that would exceed the performance of the DS3231S, but provide it in a smaller
package with lower cost, higher accuracy standards, and substantially more ruggedness. The culmination
of this work is a product family based on microelectromechanical systems (MEMS) technology.
The
DS3231M
±5ppm, I²C RTC was first introduced in 2010 with all the capability outlined in the
company’s development goals. The device has a timekeeping accuracy of ±5ppm over all conditions
including temperature, voltage, and aging. The design is extremely rugged, has achieved automotive
AEC-Q100 certification, and can sustain extreme levels of mechanical shock and variable frequency
vibration. Because of the extremely small size of the MEMS resonator, the device is packaged in a small
8-pin, 150-mil SO—something unattainable with tuning fork crystals.
Industry's First Accurate MEMS RTC
DS3231M
Industry's Most Accurate RTC
DS3231S
Industry's First 32.768kHz TCXO
DS32kHz
16-Pin SO
8-Pin SO
16-Pin SO
Integrated Crystal
WBGA Package
1999
2005
2010
3
Accurate MEMS Real-Time Clocks Product Guide
www.maximintegrated.com
Accurate MEMS RTCs at a Glance
Industry's Single Most Integrated Solutions for Accurate Timekeeping
Maxim Integrated embarked on a goal to create a quantum leap in technology advancement by developing an RTC that would
exceed performance in a smaller package, with lower cost, higher accuracy standards, and be substantially more rugged for use in
power meters, video surveillance, and automotive, industrial, and medical applications. The culmination of this work is a product
family based on the MEMS technology: the DS3231M and
DS3232M.
DS3231M
The DS3231M is the first temperature-compensated RTC with an internal MEMS resonator to reduce crystal mechanical failure.
Designed to be footprint and functionally compatible to the popular DS3231S, the DS3231M replicates the 16-pin, 300-mil SO for
users looking for a less-expensive solution but want the same functionally, firmware, and board layout found with the DS3231S.
The DS3231M integrates several important system features—resonator, RTC, TXCO, digital temperature sensor, and automatic
power switching—to support battery-backed applications in one device.
DS3232M
The DS3232M is an RTC that adds memory in the smallest package with 236 bytes of battery-backed user memory. The
DS3232M is a MEMS-equivalent to the popular
DS3232S
crystal-based RTC. Major space-saving gains are made with this
miniature MEMS resonator in the 8-pin, 150-mil package versus the 20-pin, 300-mil SO of the DS3232S.
From Crystals to MEMS
MEMS DIE
CRYSTAL BLANK
CYLINDRICAL CRYSTAL
MEMS technology, because of its size, enables significant space savings when compared to cylindrical crystals. A single MEMS
resonator occupies 47 times less area and 182 times less volume than a cylindrical crystal. This size differential allows for smaller
packaging options, provides significantly enhanced ruggedness in high vibration and shock environments, and demonstrates little
to no aging (< ±1ppm total) over the life of the device.
Simpler Assembly
•
Standard IC plastic packaging
•
Wire-bonding vs. welding
•
Ultrasonic cleaning
•
Facilitates large-scale assembly
operations
Smaller Packaging
•
8-pin (150 mil) vs. 16-pin (300 mil)
•
Chip-scale packaging (CSP) possible
Lower Cost
•
No special/custom crystals required
•
Lower cost MEMS resonator
•
Lower cost packaging
4
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Accurate MEMS Real-Time Clocks Product Guide
DS3231M Block Diagram
Automatic power switching
V
BAT
V
CC
RST
GND
POWER
SUPPLY
CONTROL
DIVIDER
32KHZ
MEMS
RESONATOR
DIGITAL
ADJUSTMENT
INTERRUPT
OR 1Hz
SELECT
INT/SQW
User-accessible
temperature sensor
3 C
TEMP
SENSOR
5ppm, 1Hz
accurate
pulse output
Each device
individually calibrated,
no blanket trims
CLOCK/CALENDAR
WITH ALARM
FACTORY TRIM
SDA
SCL
I
2
C
INTERFACE
CONTROL AND STATUS
REGISTERS
Benefits
•
Precise timekeeping accuracy (±5ppm) without user calibration
•
Low power consumption (< 3.5μA) supports battery-powered applications
•
Completely self-contained power-switching circuitry saves board space
•
Fully contained digital temperature sensor saves additional system component cost
MEMS Real-Time Clocks
Part Number
DS3231M+
DS3231MZ+
DS3231MZ/V+
DS3232MZ+
DS3232MZ/V+
+Denotes a lead(Pb)-free/RoHS-compliant package.
/V denotes an AEC-Q100-qualified part.
Package
16-SO (300 mils)
8-SO (150 mils)
8-SO (150 mils)
8-SO (150 mils)
8-SO (150 mils)
User Memory (Bytes)
—
—
—
236
236
Temp Range (ºC)
-40 to +85
-40 to +85
-40 to +85
-40 to +85
-40 to +85
AEC-Q100
—
—
✓
—
✓
5
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