LINEAR Supercapacitor-Based Power Backup System Protects Volatile Data in Handheld Devices During Power Losses. Design Note 498. Owner's Manual & User Guide.

Supercapacitor-Based Power Backup System Protects Volatile Data in Handhelds when Power Is Lost Design Note 498 Jim Drew

Introduction LTC®3226 is a 2-cell series supercapacitor charger with a

Handheld electronic devices play a key role in our everyday Power Path™ controller that simplifi es the design of backup lives. Because dependability is paramount, handhelds are systems. Specifi cally, it includes a charge pump superca- carefully engineered with lightweight power sources for pacitor charger with programmable output voltage and reliable use under normal conditions. But no amount of automatic cell voltage balancing, a low dropout regulator and careful engineering can prevent the mistreatment they a power-fail comparator for switching between normal and will undergo at the hands of humans. For example, what backup modes. Low input noise, low quiescent current and happens when a factory worker drops a bar code scan- a compact footprint make the LTC3226 ideal for compact, ner, causing the battery to pop out? Such events are handheld, battery-powered applications. The device comes electronically unpredictable, and important data stored in a 3mm × 3mm 16-lead QFN package.

in volatile memory would be lost without some form of

Backup Power Application

safety net—namely a short-term power holdup system

Figure 1 shows a power holdup system that incorporates

that stores suffi cient energy to supply standby power until

a supercapacitor stack with the capacity to provide

the battery can be replaced or the data can be stored in

standby power of 165m W for about 45 seconds in the

permanent memory.

absence of battery power. An LDO converts the output

Supercapacitors are compact, robust, reliable and can of the supercapacitor stack to a constant voltage supply support the power requirements of a backup system for during backup mode. short-term power-loss events. Like batteries, they require

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and careful charging and power regulation at the output. The Power Path is a trademark of Linear Technology Corporation. All other trademarks are the property of their respective owners.

Q1 FDC604P

LTC3226EUD

VINVIN GATE

PFI VMID X7R 1.07M R12

C+ CPO_FB 3.83M 255k C7

4.7μF LDO_FB 0.1μF

RST_FB 2.7V R9 X5R

X5R LT6703HV-3 VSB

R2 C– RST 20%

EN_CHG PFO 1.21M 80.6k

PROG CAPGOOD R11

dn498 F02

*NESS CAP ESHSR-0003C0-002R7

Figure 1. A Typical Power Backup System Using Supercapacitors