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EnerChip™ CC as Backup Power for a BQ32000 Real-Time Clock


Cymbet EnerChips are solid state rechargeable batteries having distinguishing characteristics compared to conventional rechargeable batteries. EnerChips have a high charge/discharge cycle life; low self-discharge; simple voltage controlled charging; flat discharge voltage profile; have no flammable solvents to leak or catch fire; are solder reflow tolerant; and are offered in low profile surface mount packages.

The EnerChip CC is a surface mount package containing a rechargeable solid state battery - the EnerChip - with integrated battery management that includes charge control, discharge cutoff circuitry, and a battery switchover (i.e., supply supervisory) function. EnerChips are used in applications requiring backup, bridging, or transition power to maintain real-time clock (RTC) operation or SRAM data retention in the event of main power interruption; wireless sensing as the main power source when energy can be harvested from the ambient power and used to constantly trickle charge the EnerChip; and as a power source to perform housekeeping for microcontrollers (MCUs) and peripherals when main power is interrupted, to ensure an orderly shutdown or transition to low power modes.

Many applications demand ultra low power consumption from the various system components, particularly when system power is derived from primary or rechargeable batteries. Moreover, in systems utilizing RTCs it is essential that when main power is interrupted, the standby power of the RTC be exceedingly low in order to achieve maximum run time from the backup power source. A commonly used RTC is the Texas Instruments BQ32000. The device has a VBACK pin to which a backup power source such as an EnerChip can be connected. This Application Note describes circuits utilizing the EnerChip CC - solid state energy storage integrated with battery management in a single package - as a backup power source for the BQ32000 RTC.

A typical application circuit is shown in Figure 1. Main power is fed to both the CBC3150 and BQ32000. When main power is interrupted, the EnerChip solid state battery embedded in the EnerChip CC delivers power to the RTC. The Schottky diode is placed between VOUT of CBC3150 and VBACK of BQ32000 to reduce the BQ32000 operating voltage, which in turn reduces its operating current and increases the run time in backup mode.

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