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Real-time clocks feature nonvolatile FRAM

Posted: 11 May 2007 ?? ?Print Version ?Bookmark and Share

Keywords:real-time clock? nonvolatile FRAM memory? DS32B35? DS32C35?

Dallas Semiconductor adds nonvolatile FRAM to its real-time clock (RTC) product line with the DS32B35 (2k x 8bits) and DS32C35 (8k x 8bits), said to be the industry's most accurate RTCs.

The tuning-fork crystal typically used as the time base for RTCs produces an error of 1hr/yr when exposed to temperature extremes. However, the DS32B35/DS32C35 are capable of keeping time to within 1min/yr over the temperature range of 0C to 70C because they measure temperature and adjust the crystal frequency by varying the load capacitance on the crystal.

The FRAM used in the DS32B35/DS32C35 offers true nonvolatility with no energy source required for data retention and none of the write-cycle or block-erase limitations of EEPROM or flash memory. A separate battery or capacitor can be sized for the backup requirements of the real-time clock, giving designers flexibility in the layout and sourcing of components.

Both the RTC and FRAM are accessed through an I?C interface, rather than the byte-wide interface used in battery-backed SRAM modules. For applications that have traditionally stored critical data using battery-backed SRAM modules, which require unlimited read/write cycles, the DS32B35/DS32C35 offer the ability to migrate this functionality to the I?C data bus. This migration greatly reduces the number of interconnects between the memory and CPU, thus making PCB layout easier.

The reduction in pin count and elimination of the internal backup battery allows the DS32B35/DS32C35 to be offered in a RoHS-compliant, 20-pin, 300-mil SO package, rather than the larger through-hole modules conventionally used. These RTCs are available in either the commercial (0C to 70C) or industrial (-40C to 85C) temperature range. Prices start at $4 for the DS32B35 and $4.80 for the DS32C35 for 1,000-piece quantities.

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