DS-72-34 Datasheet, PDF (7/18 Pages) Cymbet Corporation – I2C Real-Time Clock/Calendar with Integrated Backup Power

Preliminary
CBC34803 EnerChip™ RTC
Important Reference Documents for Design Information
• For complete specifications of the integrated Ambiq Micro AM0803 Real-Time Clock, see here:
http://www.cymbet.com/products/enerchip-real-time-clocks.php
• For complete specifications of the Cymbet 5µAh EnerChip and integrated power management circuit, see
this datasheet: http://www.cymbet.com/pdfs/DS-72-41.pdf .
• For an understanding of the tradeoffs in power consumption and timing accuracy when selecting a crystal
oscillator, see Application Note AN-1058 at http://www.cymbet.com/pdfs/AN-1058.pdf .
Functional Description of Integrated AM0803 Real-Time Clock
The AM0803 serves as a full function RTC for host processors such as microcontrollers. The AM0803 includes 3
distinct feature groups: 1) baseline timekeeping features with 32.768 kHz oscillator and 2) advanced
timekeeping features, and 3) basic power management features. Functions from each feature group may be
controlled via memory mapped registers. These registers are accessed using either an I2C serial interface (e.g.,
in the AM0803) or a SPI serial interface (e.g., in the AM0813). For more information on the AM0803, see here:
http://www.cymbet.com/pdfs/AM08XX_Data_Sheet_DS0002V1p0.pdf.
Low Power Operation
Minimum power operation will be achieved by turning off the CBC34803 charge pump in the power management
circuit by driving ENABLE (pin 15) low once the internal EnerChip has been charged - typically one hour to full
charge at room temperature.
The RTC has 3 low power modes, allowing the designer to make appropriate tradeoffs between power
consumption and timing accuracy. Operating current drawn by the internal RTC is as follows:
~15 nA with RC oscillator (+/- 1% timing accuracy)
~22 nA with RC oscillator and autocalibration (3-35ppm timing accuracy depending on run time)
~58 nA with crystal oscillator (+/- 2ppm timing accuracy after calibration at 25 °C)
In addition to the RTC current, the internal power management circuit typically draws 20-25nA from the EnerChip
storage device at room temperature.
The following table provides typical run times of the CBC34803 in backup mode over temperature.
Table 1: CBC34803 Backup Run Times at various RTC Modes and Temperatures
©2014-2015 Cymbet Corporation • Tel: [phone] • www.cymbet.com
DS-72-34 V.20

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