Overview: The article discusses the specifications of the STM32F103C8T6 microcontroller and explores the advantages and applications of the MAX5113 digital-to-analog converter for constant current management in demanding electrical applications.

What is an STM32F103C8T6 microcontroller?

STMicroelectronics has developed the STM32F103C8T6 microcontroller unit based on the 32-bit RISC core of the ARM Cortex-M3 processor (MCU). This microcontroller is an STM32F103 medium-density performance series member and operates up to 72 MHz.

Specification

Core

The newest generation of arm-embedded processors is the Cortex-M3 processor. 32-bit RISC ARM Cortex-M3 provides excellent performance with minimal power consumption. 

It offers an affordable platform with more pins and less power consumption that satisfies implementation requirements. It provides exceptional computing performance and an improved interrupt response mechanism.

CPU Frequency

It is the perfect option for applications that require high processing performance because it operates at a maximum frequency of 72 MHz and offers reliable processing capabilities and real-time performance. 

Memory

64KB of flash memory for storing application code and data. 20KB Static Random Memory for rapid data storage and access.

Input/Output Interfaces

The STM32F103, often referred to in contexts like the STM32 Blue Pill board, offers a more extensive set of pin configurations. 37 general-purpose input/output pins (GPIO pins) that can be configured to meet different needs for digital interfacing. 

Analog-to-digital converters (ADCs)

Two 12-bit converters that can be used to interface with analog sensors.

Serial Communication Interfaces 

It offers plenty of possibilities for communication, which includes:

  • Three USARTs
  • Two I2Cs
  • SPI interfaces

It also facilitates USB and CAN, which are used in automotive and industrial applications.

Power 

The operating voltage range is between 2.0 and 3.6 V, making it appropriate for portable and battery-powered devices. Multiple power-saving modes are included to extend battery life in portable applications. 

Submodules

To guarantee the system's overall performance, the microprocessor takes on the primary duty of directing and controlling the activity of various sub-modules. 

These submodules include:

STM32F103 Vs. Arduino Uno

While the Arduino Uno and the STM32F103 are widely used microcontroller boards, there are notable differences between them, which are seen through comparison, as shown in Table 1.

The Arduino Uno is more accessible to beginners and better suited for basic projects and educational uses. In contrast, the STM32F103 is a more potent microcontroller with improved specifications suitable for advanced applications. 

MAX5113

The MAX5113, as shown in Fig. 1, is a 9-channel, 14-bit current output, high-performance Digital-to-Analog Converter (DAC) with an SPI interface. 

Features

  • Stable operation of the system in extreme temperature conditions ranging from -40°C to +105°C is an added advantage of the system.
  • It is a high-current-output DAC chip that can deliver currents in the range of −60 mA to 300 mA.
  • The noise density can be as low as 0.5 nA/vHz at 2 mA and 56 nA/vHz at 300 mA hence, they are increasingly employed in applications requiring low signal interference.
  • One feature that makes it more flexible and appropriate for complicated multi-channel applications is its SPI interface, which enables improved control over the current output on each channel.
  • When DACs are connected in parallel, they permit high current output or higher resolution.
  • Internal references are available in MAX5113, which is the greatest advantage as it doesn't require an external reference voltage.
  • The cloak speed is up to 25 MHz, facilitating reliable data transfer.
  • An active-high asynchronous CLR input resets DAC codes to zero independent of the serial interface.
  • They are available in 3mm x 3mm 36-WLP and 5mm x 5mm 32-TQFN packages.

Fig. 1 Diagram of the MAX5112/MAX5113 Current DACs. Source Analog Devices

Advantages

  • Lower noise level and less interference with signals
  • Reduced complexity in the external circuit design
  • Increased dependability
  • Rapid switching speed
  • Enhanced efficiency
  • Robust integration
  • Elevated accuracy
  • Low distortion
  • Affordability

Understanding the MAX5113 DAC for Current Management

The MAX5113 is a flexible and high-performing current DAC ideal for demanding electrical applications, especially those requiring precise current management at the microampere level, like laser and optical systems, to obtain high-precision output. It eliminates the disadvantages associated with traditional constant current sources comprising complex circuit design.

The most important requirement of tunable laser diodes are:

  • High-precision current sources
  • High current output
  • Low noise
  • Minimal digital feedthrough

The MAX5113 DACs are well-suited for tunable laser control since they can offer all the above-mentioned desirable properties and drive a tunable laser up to 300mA. With this setup, the laser may be precisely controlled, providing consistent, high-resolution wavelength output.

It is intended to have a current sink as low as -60mA and a current source as high as 300mA. With the help of this appealing feature, one can control a semiconductor optical amplifier (SOA), which amplifies incident light through stimulated emission. 

Integration of STM32F103C8T6 and MAX5113 in Laser Constant Control Systems

The constant current driving circuit comprises MAX5113, controlled by the STM32F103C8T6 microcontroller via the SPI interface. The main goal of this system is to retain stable current output. 

The five input current channels laser can be precisely controlled with this arrangement. This system produces a reliable high-resolution output wavelength. A diagrammatic representation of the circuit structure can be found in Fig. 2. 

Fig. 2 MAX5113 in Constant Current Control Circuit. Source: MDPI

Utilizing a single-chip integrated constant current source like the MAX5113, the microcontroller can manage current output for each channel, facilitating independent control of multiple lasers. To accommodate the demands of various applications, every channel on the MAX5113 has its independent current source. 

The microcontroller connects to the MAX5113 DAC via a four-wire SPI interface. The system's peripheral circuitry is simple and consists of five high-precision resistors and the decoupling capacitors. 

This system has been evaluated, and the experimental result is that the five-way input current for the semiconductor laser can be precisely controlled by the constant current driving circuit in this system, which was built using the MAX5113.

Summarizing the Key Points

  • The STM32F103C8T6 microcontroller offers advanced features like a 32-bit ARM Cortex-M3 processor, 64KB flash memory, and multiple communication interfaces for versatile applications.
  • The MAX5113 DAC provides precise current control capabilities, ranging from -60mA to 300mA, making it ideal for laser control systems and other high-performance applications.
  • Integration of the STM32F103C8T6 with the MAX5113 DAC enables stable current output and high-resolution wavelength control in laser systems, ensuring reliable and precise operation.
  • The constant current control circuit design utilizing the STM32F103C8T6 and MAX5113 DAC allows for independent control of multiple lasers, enhancing flexibility and performance in various applications.

Reference

STMicroelectronics. “STM32F103C8 - STMicroelectronics,” https://www.st.com/en/microcontrollers-microprocessors/stm32f103c8.html.

“Applications of Current DACs | Analog Devices,” https://www.analog.com/en/resources/design-notes/applications-of-current-dacs.html.

Kong, Ling, Wenjie Lv, Haijing He, Yibo Yuan, and Libin Du. “Design of Control Circuit for Tunable Semiconductor Laser for Fiber Sensing.” Hardware 1, no. 1 (November 24, 2023): 4–28. https://doi.org/10.3390/hardware1010003.