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EnerChip™ CC as Backup Power for a DS1340 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. EnerChip storage (discharge) capacity varies by product. 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 Dallas/Maxim DS1340. The device has a VBACKUP pin to which a backup power source such as an EnerChip can be connected. Because the device has low operating current in backup mode - typically 800nA to maintain the RTC and 25nA data retention current - a miniature EnerChip device with integrated power management can provide up to several days of backup power when main power is interrupted. This Application Note describes circuits utilizing the EnerChip CC as a backup power source for the DS1340 RTC.

A typical application circuit is shown in Figure 1. Main power is fed to both the CBC31xx and DS1340. When the supply voltage drops below a specific threshold as detected by the CBC31xx, the EnerChip solid state battery embedded in the EnerChip CC delivers power to the RTC through the CBC31xx VOUT pin.

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