Make the most of your supercapacitors! Backup controller "LTC3350"

Narrow down by specifying conditions

現在2149件がヒットしています。check

ProductsPickup Power SuppliesAnalog Devices

Backup for momentary power outages and blackouts in data centers

Although the decision has been made to introduce supercapacitors as a measure against momentary power outages and blackouts, many designers may be troubled and wondering, "How should we control them?" or "What should we be careful of when adopting supercapacitors?"

There are a few things to keep in mind when using supercapacitors efficiently. Here, we will introduce some of the major issues that come with controlling supercapacitors, as well as the LTC3350 backup controller, which can make the most of supercapacitors.

Applications and challenges of supercapacitors

Supercapacitors are used as backup power sources in factories and data centers to counter momentary power outages. They have the advantage of being faster to charge than batteries and being able to release large amounts of energy all at once, but their low energy density means they are not suitable for long-term power supplies. As a backup power source, they are best suited to supplying power for a few seconds to a few tens of seconds.

Comparison table with major holding elements

	Electrolytic capacitors	Supercapacitor (Electric double layer capacitor)	Polymer Capacitors (Polymer capacitor)	battery
How to charge	Voltage	Voltage	Voltage	Voltage / Current
Discharge / charge speed	psec to msec	msec to sec	msec to sec	1 to 10 hrs
Energy density （Wh/kg）	0.01 to 0.05	1 to 5	0.01 to 0.05	8 to 600
Power Density （W/kg）	＞ 5000	＞ 4000	＞ 5000	100 to 3000
Voltage （V）	6 to 800	2.3 to 2.75	2.5 to 63	1.2 to 4.2
lifespan	＞ 100k cycles	＞ 100k cycles	No cycle limit?	150 to 1500 cycles
Operating temperature range （℃）	-20 to 100	-40 to 85	-55 to 85	-20 to 65
ESR (Equivalent Series Resistance)	Low	Low	Ultra Low	High

The items listed are general indicators for each element.

Challenges of controlling supercapacitors

What kind of challenges do you face when controlling supercapacitors? The three most common challenges are as follows:

■Extended backup time
To prevent the loss of important data, you must ensure that you have sufficient backup time.

■Extending the life of supercapacitors
The lifespan varies depending on the conditions of use, so proper control and management are important.

■ Shortening charging time
There is a demand for shorter charging times so that backup power is always available.

The LTC3350 backup controller from Analog Devices can help resolve these issues and make the most of supercapacitors. We will introduce its functions and features.

Backup controller for supercapacitors "LTC3350"

The LTC3350 is a backup controller that can efficiently supply power to one to four supercapacitors connected in series. It features Analog Devices' proprietary boost mode, which maximizes the use of limited power to extend backup time.

LTC3350 Operating Features

Specifically, the LTC3350:

LTC3350 Charging and Discharging Operation

<When charging>
The supercapacitor is charged via a step-down converter.

<When discharging>
When the power supply is interrupted, power is supplied from the supercapacitor. 2 There is a system.

(a) When Vcap > Vout, turn on the FET
The voltage of the supercapacitor (Vcap) is the output voltage (Vout), power will continue to be supplied.

(b) When Vcap < Vout, boost voltage is supplied
The voltage of the supercapacitor (Vcap) is the output voltage (Vout), it automatically switches to boost mode to maintain the required voltage.

A typical backup controller is a) Since the voltage is supplied without being changed, as the voltage of the supercapacitor drops, the device will no longer be able to maintain the voltage required by the device, and power supply will stop.

on the other hand, LTC3350 When the voltage drops, the circuit automatically switches to boost mode (b)) to maintain the required voltage. This allows for extended backup time and maximizes the use of charged power.

During discharge (boost converter)
(a) When V _cap > V _out, turn on the FET
(b) When V _cap < V _out, the voltage is boosted.

The advantage of the LTC3350 when discharging is that it is a high voltage synchronous rectification converter.
-High efficiency (long backup time)
- Compact (only one converter is needed)

What are the three functions and benefits of the LTC3350?

LTC3350 has, 3 Here are three important features:

< LTC3350 of 3 Functions
・Voltage balancer function
・Shunt regulator function
・Monitoring function

Voltage balancer function

The voltage balancer function adjusts the charge imbalance between multiple supercapacitors. If the voltage difference between the connected supercapacitors exceeds 10mV, the resistive balancer discharges the supercapacitors to adjust the charge state.

This is a common feature in battery management systems, but is not often seen in controllers for supercapacitors. A controller that can connect four supercapacitors in series is itself rare, and this is one of the features of the LTC3350.

If the voltage difference of any of the SCAPs exceeds 10mV, the resistive balancer will discharge (10mA) until the voltage difference is within 10mV.

Why is precise voltage regulation necessary?

Why do supercapacitors need precise voltage regulation?

What is the benefit of the voltage balancer function? When using multiple supercapacitors, it would be ideal if all of them were charged equally. However, in reality, there will be variations in the charge state.

If variations are allowed, some supercapacitors will remain undercharged, shortening the backup time. Voltage regulation is important to extend the backup time.

The energy E stored in a capacitor is given by the following formula:

E = ½ * C * V^2.

The higher the voltage, the more energy can be stored. However, lowering the voltage has the advantage of extending the battery life.

On the other hand, the supercapacitor that finished charging first becomes overcharged and its lifespan is shortened by the load. Also, supercapacitors have a lifetime characteristic that "if they are used at a voltage lower than the rated voltage, their lifespan can be extended."

To extend the life of a supercapacitor, precise control of the voltage is important.
Reducing the voltage can extend the life.

Lifetime characteristics of supercapacitors

Issues with using resistor dividers

Using voltage divider resistors to adjust the voltage is also possible, but this has the following issues:

<Issues with voltage adjustment using voltage dividing resistors>
・If the voltage dividing resistance is large, the internal resistance of the supercapacitor becomes dominant, making it difficult to equalize the voltage.
・If the voltage dividing resistance is small, unnecessary power consumption occurs during discharge, shortening the backup time.

By using the voltage balancer function, you can avoid these issues and achieve smooth voltage adjustment.

There is also a method to adjust the voltage of a supercapacitor using a voltage divider resistor.

Another method is to use a voltage divider resistor to make the voltage of each SCAP uniform.

But the actual resistance components are:

= R4 // R(variable)

・If R4 is large, R(variable) becomes dominant and the voltages are not uniform.
・If R4 is small, the amount of wasted power during discharge increases.

Shunt regulator function

The shunt regulator function allows a shunt current of up to 500mA to flow from a fully charged supercapacitor to a supercapacitor that is not fully charged.

The capacitors are not all the same capacity, so some will charge faster and some will charge slower.

Why are shunt regulators useful?

What is the advantage of the shunt regulator function? There are individual differences in the capacity and charging speed of supercapacitors, and there is variation in the timing at which charging is completed. With the shunt regulator function, the current that is no longer needed by a supercapacitor that has completed charging quickly can be directly passed to other supercapacitors.

Therefore, even if the remaining charge of the supercapacitors is different, it is possible to quickly adjust the balance while preventing overcharging. This also leads to efficient charging of the entire system. The shunt voltage can be finely set in 183.5μV increments.

The shunt regulator function helps maximize backup time, extend supercapacitor life, and reduce charging time.

Shunt current is useful when charging supercapacitors

To quickly charge a battery without causing an overvoltage state even if the remaining charge before charging is different or the capacity is different.

Monitoring function

LTC3350 teeth 14-bit ADC It has a built-in temperature sensor, which can monitor the voltage and current of the supercapacitor with high accuracy. It also has a built-in temperature sensor, which can monitor the temperature change of the surrounding circuits and the temperature rise due to the shunt current in real time.

In addition, capacity and ESR (equivalent series resistance) can be measured.
・Capacity measurement: "Accurate discharge current" × Calculate from "discharge time"
・ ESR Measurement: Repeatedly turn charging on and off and calculate from the voltage change

A temperature sensor is also built in, making it possible to monitor temperature rise caused by shunt current.

This data is stored in the LTC3350 and is available when needed, and periodic alerts can be sent, providing hassle-free insight into the status of the supercapacitors.

Why is monitoring necessary?

Why is a monitoring function necessary? Supercapacitors deteriorate with use, decreasing their capacitance and increasing their ESR. This reduces the backup time, and if left unchecked, the backup time that was initially designed cannot be secured.

The figure below is a graph showing the measured data of a load life test of a certain supercapacitor product. It can be seen that the capacitance decreases and the ESR increases with age.

Lifetime characteristics of supercapacitors

Understanding the condition of supercapacitors is important!

In order to maintain an appropriate backup time, it is important to know the condition of the supercapacitor and replace it at the appropriate time. If the controller does not have a monitoring function, some other mechanism is required.

By utilizing the monitoring functions of the LTC3350, it is possible to grasp the status of the supercapacitor in real time and properly manage its lifespan.

This time, we introduced the LTC3350, a backup controller for supercapacitors. By using the LTC3350, you can simultaneously solve the issues that arise when controlling supercapacitors: maximizing backup time, managing the lifespan of the supercapacitor, and shortening charging time.

We have an evaluation board available, so please give it a try. If you are interested, please feel free to contact us.

Application example

Measures against momentary and power outages in data centers
Countermeasures against momentary power outages and power outages in semiconductor manufacturing equipment and factories