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ST intros factory-calibrated serial real-time clocks

Posted: 07 Mar 2007 ?? ?Print Version ?Bookmark and Share

Keywords:real-time clock? oscillator? ST? oscillators? RTC IC?

STMicroelectronics announced its 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.

The M41T83 and M41T93 RTCs, in embedded-crystal packages, are pre-calibrated to 5ppm. These two devices share the same specifications: the M41T83 includes a 400kHz I?C interface, while the M41T93 uses a 10MHz SPI bus. The parts introduce timekeeping features including analog calibration, a programmable auto-reload counter/timer and dual alarms. In addition to the factory-programmed register, an additional analog calibration register is included that 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 that defines the threshold for the automatic back-up switchover circuit. The RTCs' 450nA backup current (typical) makes them suitable for capacitor-backed applications, battery backup and accurate timekeeping 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 12bytes of NVRAM, and an oscillator-fail detection circuit, a programmable square-wave generator and a watchdog. The M41T83 and M41T93 are available in 4-by-4mm QFN16 package for use with an external crystal.

Samples of the device are available. Pricing begins at 70 cents in volume quantities.

- Emily Gleason
eeProductCenter




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