1. Linear Technology Corporation
LTC3350: High Current Supercapacitor Backup Controller & System Monitor
Tony Armstrong Director of Product Marketing
Power Products
April, 2014

2. LTC3350: The Problem It Solves
Basic Problem: Many apps need a few seconds of backup time…
Capacitors provide simple, reliable and inexpensive short-term backup energy.
Monitoring capacitor “state of health” important for two reasons:
Ensure adequate energy and power handling for proper backup
Extend capacitor lifetime by minimizing capacitor charge voltage
What Basic Circuit Building Blocks Are Required to Accomplish This?
High power charger for quickly charging backup capacitor stack
High power backup dc/dc for providing regulated backup supply
Power path control, VIN / VCAP monitor
Capacitor balancer and overvoltage protection
Capacitor health monitor (stack capacitance and stack ESR measurement system) 2

3. Supercapacitor Lifetime Characteristics
Supercap “end of life” = 30% drop in capacitance or 100% increase in ESR
Supercap lifetime degrades faster at high temps 3

4. Supercapacitor Lifetime Degrades at High Temps
Backup Energy (Joules required) = Backup Power*Backup Time
Measuring stack capacitance and VCAP  Joules available
VCAP can be reduced if Joules available >> Joules required
Reducing VCAP increases Cap lifetime ! 4

5. LTC3350: High Current Supercapacitor Backup Controller and System Monitor: few helpful equations…

6. LTC3350: What is it? High Current Supercapacitor Backup Controller and System Monitor

7. LTC3350 Supercap Charger, Backup Controller and SCAP Health Monitor
Why did we develop this part?
Provide high current cap charging and balancing for 12V systems
Provide integrated cap health and system monitoring
Provide seamless power path control
Provide high efficiency bi-directional power flow to make optimum use of available input power and CAP stored energy
Who might use it?
Servers, data storage systems
Data backup supplies
High Capacity Solid State Drives 7

8. LTC3350 Key Features 4.5V - 40V input / output range
High current sync buck charging of 1-4 supercapacitors
High current sync boost backup mode for max capacitor energy use
Automatic cell balancing, OV shunts and power-path control
Internal 14-bit ADC for accurate cap health and system monitoring
Measure capacitance
Measure capacitor ESR
Measure VIN, IIN, VCAP, ICAP
I2C interface for data monitoring and capacitor charge control (VCAP adjust)
All N-FET design 8

9. LTC3350 Power Path Control Normal Mode VOUT = VIN
CAPS charged from VOUT 9

10. LTC3350 Power Path Control Backup Mode VOUT = VCAP VCAP > 5V
Set min VOUT
VOUT = VCAP
VCAP > 5V
Linear Discharge 10

11. LTC3350 Power Path Control Backup Mode VOUT = 5V VCAP < 5V
Set min VOUT
VOUT = 5V
VCAP < 5V
Boost Mode 11

12. LTC3350 Typical Backup Operation12

13. LTC3350: Block Diagram 13

14. LTC3350: QFN Package

15. LTC3350 Typ App: SCAP Charger + Backup
12V, 5A Supercapacitor Charger with 2A Input Current Limit and 6V, 25W Backup Mode 15

16. LTC3350: Demo Board
Active area: X = 4.1cm Y = 2.6cm 16

17. LTC3350: Summary
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