Supercapacitor Interface IC

Customized Supercapacitor Interface Circuitry for Different Applications

Supercapacitors are proliferating given their high energy density versus normal capacitors, low effective series resistance (ESR), and high durability compared to conventional batteries when it comes to repeated charging. To effectively design with supercapacitors, supporting interface circuitry for the following functions is typically required:

  • Active Cell Balancing
  • Supercapacitor Charging & Discharging
  • Maintaining a Fixed Output Voltage
  • Electrolyte Dry-Up Detection
  • Monitoring Ripple Current and Temperature
  • Reverse Voltage, Overcharging & Short Circuit Protection

GreenPAK™ products are an ideal solution for performing many of these supporting functions to supercapacitor-based systems. Unlike dedicated ICs that are costly and specialized with limited capability, GreenPAK parts are competitively priced, can be quickly customized with programmable thresholds and timing, and eliminate many external setting components.


GreenPAK Benefits for Supercapacitor Interface Circuitry

Flexibility

  • Tailor solutions for your specific supercapacitor selection and system management
  • Completely configurable Asynchronous State Machine, logic, and I/O
  • Programmable thresholds and timing ensures everything is optimized for your system

Small Size

  • Choose the smallest GreenPAK part that meets your needs with sizes starting at 1.2mm²
  • Configure only the functions you require to make efficient use of GreenPAK IC resources
  • Eliminates the need for many external setting components

Low Cost

  • Competitively-priced GreenPAK solutions open new markets as they enable supercapacitor technology in previously cost-prohibitive applications

Example Supercapacitor Interface Circuits

Find example supercapacitor interface circuits in the Related Resources section of this webpage, including a Design Toolkit application note and reference designs for supercapacitor active cell balancing and charging. Each of these resources has an associated open-source GreenPAK designer file that can be modified for any design.

Highlighted below are two of the many example functions that GreenPAK can be configured to do.

Active Cell Balancing

Supercapacitors that are rated for 5.5V are often a stack of two cells with a rated voltage of 2.7V each. Similarly, higher voltage supercapacitor modules (e.g. rated for 48V or more) have even more stacked cells to achieve their rated voltages. Cell balancing is required to ensure that each cell stays within its rated voltage because inevitable cell mismatches will cause overvoltage fault conditions during operation. A simple modular supercapacitor active cell balancing solution using GreenPAK is shown in Fig. 1 and the corresponding GreenPAK design implementation is shown in Fig. 2.

Key Design Considerations

  • When the voltage across the supercapacitor reaches its charging threshold, an active cell balancing circuit allows current to flow through a balancing resistor. GreenPAK has analog comparators with voltage references that can configured for specific application requirements.
  • To signal overcharging, a FLAG output can be configured to go HIGH if the voltage across the supercapacitor remains too high for more than a set time period. GreenPAK’s fully programmable CNT/DLY blocks provide flexibility to work with a wide range of timing configurations.
  • Each cell balancing module can be stacked on top of each other to create a system that can charge several stacked supercapacitors in series.
  • The ESD diode is optional, but is recommended for applications where the supercapacitor is removable by the user.

Figure 1. Supercapacitor Active Cell Balancing Circuit

Figure 2. GreenPAK Active Cell Balancing Implementation

Supercapacitor Charging & Discharging

A GreenPAK with integrated power switches can be configured to charge and discharge a 1-cell supercapacitor as shown in the Fig. 3 circuit and corresponding Fig. 4 GreenPAK design implementation.

Key Design Considerations

  • A supercapacitor power management circuit should charge a supercapacitor up to a pre-determined voltage and then discharge it when the main voltage supply drops below a set voltage. Every GreenPAK includes several GPIOs, Look Up Tables, ACMPs, and counters which can be configured to do this.
  • In order to allow an external host controller to determine when to begin charging the supercapacitor, the GreenPAK can be easily configured to receive a Charge_EN signal on one of its GPIO pins.
  • It’s common to have a bypass mode which powers the load directly from the main power supply, a charging mode to charge the supercapacitor, and a discharging mode when the supercapacitor must power the load. Users can customize GreenPAK to implement all of these modes as shown in Fig. 4.

Figure 3. 1-Cell Supercapacitor Charging Circuit

Figure 4. GreenPAK 1-Cell Charging Implementation

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