30 min

Step down the input voltage with MP9943A and STM32F429NI to achieve the desired output level

Power down, boost efficiency

Buck 9 Click with Fusion for STM32 v8

Published Jul 31, 2023

Click board™

Buck 9 Click

Development board

Fusion for STM32 v8


NECTO Studio



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Hardware Overview

How does it work?

Buck 9 Click is based on the MP9943, a high-efficiency 3A peak, 36V, synchronous step-down converter with Power Good from Monolithic Power Systems (MPS). The MP9943 utilizes a peak-current-mode control architecture, ensuring an exceptional transient response and stabilization of the feedback loop. Besides its protection features, MP9943 is also equipped with a soft-start function and a sync option, making this Click board™ a handy solution for developing applications that require a regulated power supply. The feedback voltage on the FB pin of the converter determines the output voltage, and thanks to a voltage divider and an SMD jumper labeled VOUT SEL, which can connect one of two available voltage divider resistors, it allows the output to be set to either 3.3V or 5V. The MP9943 has other advanced features, including synchronization with the external clock from 200kHz to 2.2MHz over the EN/SYNC pin routed to the mikroBUS™ ESY (default PWM) pin. The same pin is also used

as a Chip Enable for the device. The MP9943 operates at a high (fixed) switching frequency of 410kHz, allowing a good compromise between the efficiency and the size of the external components. Thanks to its ability to work with the high-duty cycle of the internal switching PWM signal, the MP9943 requires the input voltage to be only about 0.7V above the output voltage to maintain the regulation. However, the device cannot operate properly if the input voltage drops under 3.3V. Therefore, the under-voltage protection shuts down the device as a protection measure. The under-voltage protection is disabled once the input voltage exceeds 3.5V. This small hysteresis of 0.2V prevents erratic behavior in border cases. Therefore, the supply at the input terminal should stay between 4V and 36V. However, if the output voltage is set to 5V, the voltage at the input should be approximately 5.8V to 6V at least to provide good regulation at the output. The over-current protection is based on cycle-by-cycle limiting

of the inductor current. If the output voltage drops during the current limiting interval, causing the FB voltage to fall under 84% of the internal reference, the device enters the hiccup mode, shutting down the output. After a fixed period, the device will try to re-enable the output. If the short-circuit condition still exists, it will shut down the output again, repeating the whole process until the short-circuit condition disappears. The hiccup mode greatly reduces the short-circuit current, protecting the device when the output is shorted to ground. This Click board™ can be operated only with a 3.3V logic voltage level. The board must perform appropriate logic voltage level conversion before using MCUs with different logic levels. Also, this Click board™ comes equipped with a library containing easy-to-use functions and an example code that can be used as a reference for further development.

Buck 9 Click hardware overview image

Features overview

Development board

Fusion for STM32 v8 is a development board specially designed for the needs of rapid development of embedded applications. It supports a wide range of microcontrollers, such as different 32-bit ARM® Cortex®-M based MCUs from STMicroelectronics, regardless of their number of pins, and a broad set of unique functions, such as the first-ever embedded debugger/programmer over WiFi. The development board is well organized and designed so that the end-user has all the necessary elements, such as switches, buttons, indicators, connectors, and others, in one place. Thanks to innovative manufacturing technology, Fusion for STM32 v8 provides a fluid and immersive working experience, allowing

access anywhere and under any circumstances at any time. Each part of the Fusion for STM32 v8 development board contains the components necessary for the most efficient operation of the same board. An advanced integrated CODEGRIP programmer/debugger module offers many valuable programming/debugging options, including support for JTAG, SWD, and SWO Trace (Single Wire Output)), and seamless integration with the Mikroe software environment. Besides, it also includes a clean and regulated power supply module for the development board. It can use a wide range of external power sources, including a battery, an external 12V power supply, and a power source via the USB Type-C (USB-C) connector.

Communication options such as USB-UART, USB HOST/DEVICE, CAN (on the MCU card, if supported), and Ethernet is also included. In addition, it also has the well-established mikroBUS™ standard, a standardized socket for the MCU card (SiBRAIN standard), and two display options for the TFT board line of products and character-based LCD. Fusion for STM32 v8 is an integral part of the Mikroe ecosystem for rapid development. Natively supported by Mikroe software tools, it covers many aspects of prototyping and development thanks to a considerable number of different Click boards™ (over a thousand boards), the number of which is growing every day.

Fusion for STM32 v8 horizontal image

Microcontroller Overview

MCU Card / MCU



8th Generation


ARM Cortex-M4

MCU Memory (KB)


Silicon Vendor


Pin count


RAM (Bytes)


Used MCU Pins

mikroBUS™ mapper

Power Supply
Device Enable

Take a closer look


Buck 9 Click Schematic schematic

Step by step

Project assembly

Fusion for PIC v8 front image hardware assembly

Start by selecting your development board and Click board™. Begin with the Fusion for STM32 v8 as your development board.

Fusion for PIC v8 front image hardware assembly
GNSS2 Click front image hardware assembly
SiBRAIN for PIC32MZ1024EFK144 front image hardware assembly
GNSS2 Click complete accessories setup image hardware assembly
v8 SiBRAIN Access MB 1 - upright/background hardware assembly
Necto image step 2 hardware assembly
Necto image step 3 hardware assembly
Necto image step 4 hardware assembly
NECTO Compiler Selection Step Image hardware assembly
NECTO Output Selection Step Image hardware assembly
Necto image step 6 hardware assembly
Necto image step 7 hardware assembly
Necto image step 8 hardware assembly
Necto image step 9 hardware assembly
Necto image step 10 hardware assembly
Necto PreFlash Image hardware assembly

Track your results in real time

Application Output

After pressing the "FLASH" button on the left-side panel, it is necessary to open the UART terminal to display the achieved results. By clicking on the Tools icon in the right-hand panel, multiple different functions are displayed, among which is the UART Terminal. Click on the offered "UART Terminal" icon.

UART Application Output Step 1

Once the UART terminal is opened, the window takes on a new form. At the top of the tab are two buttons, one for adjusting the parameters of the UART terminal and the other for connecting the UART terminal. The tab's lower part is reserved for displaying the achieved results. Before connecting, the terminal has a Disconnected status, indicating that the terminal is not yet active. Before connecting, it is necessary to check the set parameters of the UART terminal. Click on the "OPTIONS" button.

UART Application Output Step 2

In the newly opened UART Terminal Options field, we check if the terminal settings are correct, such as the set port and the Baud rate of UART communication. If the data is not displayed properly, it is possible that the Baud rate value is not set correctly and needs to be adjusted to 115200. If all the parameters are set correctly, click on "CONFIGURE".

UART Application Output Step 3

The next step is to click on the "CONNECT" button, after which the terminal status changes from Disconnected to Connected in green, and the data is displayed in the Received data field.

UART Application Output Step 4

Software Support

Library Description

This library contains API for Buck 9 Click driver

Key functions:

  • buck9_set_device_mode - This function enables and disables output of this board

Open Source

Code example

This example can be found in NECTO Studio. Feel free to download the code, or you can copy the code below.

 * @file main.c
 * @brief Buck 9 Click Example.
 * # Description
 * Demo application shows basic usage of Buck 9 click.
 * The demo application is composed of two sections :
 * ## Application Init 
 * Configuring clicks and log objects.
 * Settings the click in the default configuration.
 * ## Application Task  
 * Enable and Disable device every 5 seconds.
 * @author Stefan Ilic

#include "board.h"
#include "log.h"
#include "buck9.h"

static buck9_t buck9;   /**< Buck 9 Click driver object. */
static log_t logger;    /**< Logger object. */

void application_init ( void ) {
    log_cfg_t log_cfg;  /**< Logger config object. */
    buck9_cfg_t buck9_cfg;  /**< Click config object. */

     * Logger initialization.
     * Default baud rate: 115200
     * Default log level: LOG_LEVEL_DEBUG
     * @note If USB_UART_RX and USB_UART_TX 
     * are defined as HAL_PIN_NC, you will 
     * need to define them manually for log to work. 
     * See @b LOG_MAP_USB_UART macro definition for detailed explanation.
    LOG_MAP_USB_UART( log_cfg );
    log_init( &logger, &log_cfg );
    log_info( &logger, " Application Init " );

    // Click initialization.

    buck9_cfg_setup( &buck9_cfg );
    BUCK9_MAP_MIKROBUS( buck9_cfg, MIKROBUS_1 );
    if ( buck9_init( &buck9, &buck9_cfg ) == DIGITAL_OUT_UNSUPPORTED_PIN ) {
        log_error( &logger, " Application Init Error. " );
        log_info( &logger, " Please, run program again... " );

        for ( ; ; );
    log_info( &logger, " Application Task " );

void application_task ( void ) {
    buck9_set_device_mode ( &buck9, BUCK9_DEVICE_ENABLE );
    log_printf(&logger, "Output:\t ENABLED\r\n");
    Delay_ms( 5000 );
    buck9_set_device_mode ( &buck9, BUCK9_DEVICE_DISABLE );
    log_printf(&logger, "Output:\t DISABLED\r\n");
    Delay_ms( 5000 );

void main ( void ) {
    application_init( );

    for ( ; ; ) {
        application_task( );

// ------------------------------------------------------------------------ END

Additional Support