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LTC3350 Backgrounder High Current Supercapacitor Backup Controller & System Monitor

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Linear Technology Corporation

Background

Many applications require reliable short-term uninterrupted power in the event of a main power failure.  Examples include data backup for solid state drives (SSDs), power fail alarms in medical and industrial applications as well as a host of other “dying gasp” power fail indicators.  

Supercapacitors provide a simple and inexpensive source of short-term backup energy. They lack many of the safety and cycle life tradeoffs associated with batteries, and provide excellent power density for high current backup.  However, supercapacitors suffer from lost capacity and increased ESR over time, particularly at high operating temperatures.  Therefore, monitoring capacitor “state of health” in a capacitor-based backup system is important for two reasons:

1.To ensure adequate energy and power handling for proper backup

2.To extend capacitor lifetime by minimizing capacitor charge voltage

 The building blocks required to produce a reliable, capacitor-based uninterrupted power supply consist of the following: 

•High power charger for quickly charging backup capacitor stack

•High power backup dc/dc for providing regulated backup supply 

•Power path control, VIN / VCAP monitors 

•Capacitor balancer and overvoltage protection 

•Capacitor health monitor (stack capacitance and stack ESR measurement system)

Introduction

The LTC3350 is a new IC that contains all power path control, capacitor stack charging and balancing, and capacitor “health” monitoring circuitry necessary to provide a complete, standalone high-reliability backup system. The LTC®3350 can charge and monitor a series stack of one to four supercapacitors. The device’s synchronous step-down controller drives N-channel MOSFETs for constant current/constant voltage charging, and can run in reverse as a step-up converter to deliver power from the supercapacitor stack to the backup supply rail.  Internal balancers eliminate the need for external balance resistors and each capacitor has a shunt regulator for overvoltage protection.  All system currents and voltages as well as stack capacitance and ESR are accurately measured using an internal 14-bit ADC and can be read back via I2C interface.   In addition, operating parameters such as capacitor charging voltage may be programmed via I2C to optimize system lifetime and performance.

Key Technical Features

•High Efficiency Synchronous Step-Down CC/CV Charging of One to Four Series Supercapacitors

•Step-Up Mode in Backup Provides Greater Utilization of Stored Energy in Supercapacitors

•14-Bit ADC for Monitoring System Voltages/Currents, Capacitance and ESR

•Active Overvoltage Protection Shunts

•Internal Active Balancers – No Balance Resistors

•VIN: 4.5V to 35V, VCAP(n): Up to 5V per Capacitor, 

        Charge/Backup Current: 10+A

•Programmable Input Current Limit Prioritizes System Load Over Capacitor Charge Current

•Dual Ideal Diode PowerPath™ Controller

•All N-FET Charger Controller and PowerPath Controller

•Compact 38-Lead 5mm × 7mm QFN Package

 

Target Applications

•High Current 12V Ride-Through UPS (Uninterruptable Power Supply)

•Servers/Mass Storage/High Availability Systems

 

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