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35V controller for hot swappable supercapacitor backup power

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By Nick Flaherty

The LTC3351’s integrated hot swap controller and circuit breaker use N-channel MOSFETS to provide a low loss power path from the input to the output, plus foldback current limiting to reduce inrush current. The device enables reliable short term uninterrupted power in the event of a main power failure for applications such as solid-state drives (SSDs) and nonvolatile dual in-line memory modules (NVDIMMs) data backup, power fail alarms in medical and industrial applications and “dying gasp” power fail indicators using PowerPath control, capacitor stack charging and balancing, protection and capacitor health monitoring. Other applications include high current 12V ride-through supplies and short term uninterruptible power supplies (UPS) for servers, mass storage and high availability systems.

The 4.5V to 35V input voltage range and over 10A of charge/backup current capability is suppported by balancing and overvoltage protection for a series stack of one to four supercapacitors while the synchronous step-down controller enables constant current/constant voltage charging of the capacitor stack at up to 5V per cell. In backup mode, the step-down converter runs in reverse as a synchronous step-up DC-DC to deliver power from the supercapacitor stack to the system supply to be backed up, while the hot swap controller provides programmable UV/OV thresholds, PCIe compatible start-up timing and a precision threshold /RETRY input.

The controller includes a16bit analogue-to-digital converter (ADC) which continuously monitors input and output voltage and current, and the internal measurement system monitors parameters associated with the backup capacitors themselves, including capacitor stack voltage, capacitance and stack ESR (equivalent series resistance) to ensure adequate energy storage and power delivery during backup.  By monitoring the actual capacitance of the backup supercapacitors, the LTC3351 provides longer capacitor life by enabling the system to set the capacitor voltage to a minimum value while ensuring the required backup energy is maintained.  All the system parameters and fault status can be monitored via a 2-wire I2C interface, and alarm levels can be set to alert the system to a sudden change in any of these measured parameters.

The LTC3351 is available in a thermally enhanced 44-lead, low profile (0.75mm) 4mm x 7mm QFN package. The device operates over a –40°C to 125°C junction temperature range and is available from stock.

www.linear.com/product/LTC3351

 

 

Summary of Features: LTC3351

 

Integrated Hot Swap Controller with Circuit Breaker

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

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

16-Bit ADC for Monitoring System Voltages/Currents, Capacitance & ESR

Programmable Undervoltage & Overvoltage Thresholds to 35V

VIN: 4.5V to 35V, VCAP(n): Up to 5V per Capacitor, Charge/Backup Current: >10A

Programmable Input Current Limit Prioritizes System Load Over Capacitor Charge Current

All N-FET Charger Controller & PowerPath™ Controller

Compact 44-Lead 4mm x 7mm QFN Package

 


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