STMicroelectronics introduces factory-calibrated serial real-time clocks
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STMicroelectronics introduces factory-calibrated serial
real-time clocks
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STMicroelectronics has
announced its first serial
real-time clock (RTC) chips
with factory calibration,
enabling manufacturers using
the parts to simplify assembly
and test operations by
omitting the time-consuming
calibration step.
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Tyco Electronics has
introduced a new
generation of surface
mount automotive
connectors
The new M41T83 and M41T93 RTCs, in embedded-crystal packages, are
pre-calibrated to plus or minus 5ppm, delivering a new level of accuracy to users of
time-of-day clock and calendar devices. Using a one-time programmable (OTP)
register, ST trims the internal load capacitance of the 32.768 kHz on-chip oscillator
during factory test, ensuring that the parts are accurate to within 12 seconds per
month.
Apart from the serial interfaces, these two new devices share the same
specifications: the M41T83 includes a 400 kHz I2C interface, while the M41T93
uses a 10 MHz SPI bus, the world’s first RTC to operate at this speed. The parts
introduce a number of advanced timekeeping features including analog calibration,
a programmable auto-reload counter/timer, and dual alarms.
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In addition to the factory-programmed register, an additional analog calibration
register is included which allows the user to override the factory calibration
settings. This can be beneficial to adjust for the ambient temperature or to
compensate for the effects of stray capacitance on the board. This second register
is also needed in applications using the crystal-less QFN16 package option.
Oscillator adjustments appear immediately in the test output to give instantaneous
feedback to the user.
The auto-reload counter/timer can be used with one of four user-selectable source
clocks to generate timing waveforms and to provide periodic processor interrupts.
The dual programmable alarms output on separate pins for applications requiring
multiple alarm times.
Both devices include an on-board precision voltage reference which exactly defines
the threshold for the automatic back-up switchover circuit. The RTCs’ low 450nA
backup current (typical) makes them suitable for capacitor-backed applications as
well as for battery backup, and with ST’s low-power process technology, accurate
timekeeping is ensured down to 1.8V. A built-in battery monitor checks the
back-up voltage and indicates when the battery should be replaced.
Other features include 12 bytes of NVRAM, and an oscillator-fail detection circuit
which sets a bit if the oscillator drops more than three pulses, indicating that the
back-up voltage might have fallen low enough to affect timekeeping – a situation
that might occur during brownout in capacitor-backed applications. A
programmable square-wave generator and a watchdog are also included.
When VCC fails and the device automatically switches to backup, it generates a
Reset signal which is held for 200ms after power is restored. This Power-on
Reset/Low-Voltage Detect function can save the designer from needing a separate
Reset IC on the board. Three voltage levels are available for the switchover and
reset thresholds (nominally 2.93V, 2.63V and 2.32V) which are specified in the
part number when ordering. In addition to the pre-calibrated embedded crystal
http://www.anglia.com/newsarchive/1643.asp (1 of 2) [18/07/2007 11:40:24]
STMicroelectronics introduces factory-calibrated serial real-time clocks
package, the M41T83 and M41T93 are also available in ST’s space saving, low-cost
4mm x 4mm QFN16 package for use with an external crystal.
For cost-sensitive applications that nevertheless require mid-range real-time clock
features, the low-cost M41T82 variant offers a reduced feature set of the M41T83.
It eliminates the watchdog, square-wave generator and alarms, but retains the
400kHz I2C interface, analog user calibration, precision switchover reference,
battery monitor, 12 bytes of NVRAM and reset output, and is supplied in a small
footprint, low-cost 8-lead SOIC.
For more information on the full range of STMicroelectronics products available
from Anglia please call +44 (0)1945 474747 or email info@anglia.com
Alternatively, click on this link to go to the main STMicroelectronics section where
you can view other news articles and product data.
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This news article was originally published in July 2007.
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5/7/07
http://www.anglia.com/newsarchive/1643.asp (2 of 2) [18/07/2007 11:40:24]