TIDUFK2 September   2026

 

  1.   1
  2.   Description
  3.   Resources
  4.   Features
  5.   Applications
  6.   6
  7. 1System Description
    1. 1.1 Terminology
    2. 1.2 Key System Specifications
  8. 2System Overview
    1. 2.1 Block Diagram
    2. 2.2 Design Considerations
      1. 2.2.1 Processing
      2. 2.2.2 Voltage and Current Sensing
        1. 2.2.2.1 Voltage Measurement
        2. 2.2.2.2 Current Measurement
      3. 2.2.3 Solenoid – Relay Driver
      4. 2.2.4 Temperature Measurement
    3. 2.3 Highlighted Products
      1. 2.3.1 CC2340R53
      2. 2.3.2 OPA2323
      3. 2.3.3 DRV8213
      4. 2.3.4 TMP236A2
  9. 3System Design Theory
    1. 3.1 Software Architecture
      1. 3.1.1 System Initialization
      2. 3.1.2 Sample Acquisition
      3. 3.1.3 Sample Processing and Task Prioritization
    2. 3.2 Circuit Breaker Functionality
      1. 3.2.1 Breaker State and Relay Control
      2. 3.2.2 Instantaneous Short-Circuit Trip
      3. 3.2.3 Inverse-Time Overload Trip
    3. 3.3 Electrical Metrology
    4. 3.4 Zigbee Connectivity
  10. 4Hardware, Software, Testing Requirements, and Test Results
    1. 4.1 Hardware Requirements
      1. 4.1.1 Hardware Connections and Test Points
    2. 4.2 Test Setup
      1. 4.2.1 Connecting the TIDA-011030 to the Metering Test Equipment
      2. 4.2.2 Power-Supply Options
      3. 4.2.3 Metrology Calibration
      4. 4.2.4 Test-Data Acquisition and Error Calculation
    3. 4.3 Test Results
      1. 4.3.1 Relay Control and Protection
        1. 4.3.1.1 Relay Pull-In and Holding PWM
        2. 4.3.1.2 Instantaneous Trip and Relay-Opening Latency
        3. 4.3.1.3 Inverse-Time Overload Trip
      2. 4.3.2 Metering
      3. 4.3.3 Real-Time Software Performance
      4. 4.3.4 Zigbee Functional Test
  11. 5Design and Documentation Support
    1. 5.1 Tools and Software
      1. 5.1.1 Tools
      2. 5.1.2 Software
    2. 5.2 Documentation Support
    3.     Trademarks
  12. 6About the Author

2.2.3 Solenoid – Relay Driver

This circuit breaker reference design uses an electromechanical relay to connect and disconnect the load. Conventional circuit breakers interrupt the current through mechanically latched power contacts and use a dedicated trip mechanism, commonly including a magnetic solenoid for rapid actuation under short-circuit conditions. For this demonstration, an electromechanical relay provides a simple and repeatable electrically controlled substitute for the final mechanical switching mechanism.

Although the relay does not represent the full interrupting capability of a certified circuit breaker, the inductive coil imposes similar requirements on the actuator driver, including sufficient pull-in current, reduced holding power, rapid de-energization, and safe handling of the stored inductive energy.

TIDA-011030 Relay Driver CircuitFigure 2-6 Relay Driver Circuit

The relay coil is driven by a DRV8213 integrated H-bridge driver. Compared with a discrete transistor driver, the H-bridge provides controlled current paths during drive and brake operation and eliminates the need for a separate flyback diode across the coil.

The DRV8213 also integrates current sensing and current regulation. The IPROPI output provides an analog signal proportional to the relay-coil current and is connected to the CC2340R53 through the DRV_FB_I signal. This feedback signal allows the controller to verify that the coil draws the expected current and can later be used to detect an open coil, mechanical blockage, or other faults.

Independent current regulation protects the driver and coil against excessive current. GAINSEL is connected to ground, selecting an IPROPI current-mirror gain of:

Equation 22. AIPROPI=205μA/A

At the maximum relay current of 0.28A, the IPROPI output current is:

Equation 23. IIPROPI=0.28A×205μA/A=57.4μA

With the selected IPROPI resistance of 8.2kΩ, this produces:

Equation 24. VIPROPI=57.4μA×8.2kΩ=0.471V

The DSG package uses an internal nominal reference voltage of 510mV. The nominal current-regulation threshold is therefore:

Equation 25. ILIMIT=0.510V205μA/A×8.2kΩ=0.303A

When the IPROPI voltage reaches the reference voltage, the DRV8213 limits the coil current using its internal fixed-off-time current-regulation mechanism. Capacitor C26 filters short switching transients to prevent premature current regulation.

The DRV8213 is controlled by two PWM inputs IN1 and IN2 as listed in Table 2-1.

Table 2-1 DRV8213 H-Bridge Control
Operating modeIN1IN2H-bridge state
Coast / relay open00High-Z
Forward drive10Coil actively energized
Brake / slow decay11Both outputs driven low

To close the relay, IN1 is set high and IN2 is held low for approximately 100ms, applying the full supply voltage to the coil. After pull-in, IN2 alternates between forward drive and brake at 20kHz to reduce the average holding current. A 35% effective drive duty cycle requires IN2 to remain low for 35% and high for 65% of each PWM period. During the high interval, the H-bridge enters the brake/slow-decay state and allows the coil current to recirculate. To open the relay, both inputs are set low, placing the H-bridge in coast mode and allowing the coil current to decay.

External 100kΩ pull-down resistors are connected to IN1 and IN2. They keep both control inputs low while the CC2340R53 is held in reset, unpowered, or the GPIOs are still configured as high-impedance inputs. The resulting default state is coast mode, in which the H-bridge outputs are disabled and the relay is de-energized. The external resistors complement the pull-down resistors integrated into the DRV8213 and provide a defined hardware-safe state independent of MCU initialization.