Application Note
EnerChip™ CC as Backup Power for a DS1390 Real-Time Clock
Introduction
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 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.
AN-1043
Figure 1. Typical Application Circuit Using the EnerChip CC and DS1390 Real-Time Clock.
Doc AN-72-1043 Rev B
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