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EnerChip™ CC as Backup Power for a DS1390 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.

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 DS1390. 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 500nA at 3V - a miniature EnerChip device with integrated power management can provide up to several days of backup power to the RTC when main power is interrupted. This Application Note describes circuits utilizing the EnerChip CC as a backup power source for the DS1390 RTC.

A typical application circuit is shown in Figure 1. Main power is fed to both the CBC31xx and DS1390. 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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