AN-1042

Application Note

©2011 Cymbet Corporation • Tel: +1-763-633-1780 • www.cymbet.com

Doc AN-72-1042 Rev B

Page 1 of 3

EnerChip™ CC Backup Power for Epson RX-8564 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 Epson RX-8564.

Because the device has low operating current in backup mode - typically 275nA 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 use of the EnerChip CC - solid state energy storage

integrated with battery management in a single package - as a backup power source for the RX-8564 RTC.

A typical application circuit is shown in Figure 1. Main power is fed to the CBC31xx, which in turn powers the

RX-8564. 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.

Figure 1. Typical Application Circuit Using the EnerChip CC and Epson RX-8564 Real-Time Clock.