AN-1047

Application Note

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

Doc AN-72-1047 Rev A

Page 1 of 3

Preliminary

EnerChip™ CC Real-Time Clock Backup for K60 Microcontroller

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. In systems utilizing stand-alone or

embedded RTCs, it is essential that the standby power of the RTC be very low in order to achieve maximum

run time from the backup power source when main power is interrupted. A low power MCU now available from

Freescale is the K60 family. The device has a VBAT auxiliary power pin to which a backup power source can be

connected. This Application Note describes use of the surface mount EnerChip CC as the backup power source

for the RTC embedded within the K60 MCU.

A typical application circuit is shown in Figure 1. Main power is fed to both the CBC31xx and K60 MCU. 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 MCU VBAT pin from the CBC31xx VOUT pin.

Figure 1. Application Circuit Using the EnerChip CC to Maintain the Real-Time Clock Within the K60 MCU.