Efficiently regulate negative voltages with MCP16331 and STM32L073RZ
Voltage flexibility unleashed
Published Feb 26, 2024
Click board™
MCP16331 INV Click
Dev. board
Nucleo-64 with STM32L073RZ MCU
Compiler
NECTO Studio
MCU
STM32L073RZ
Experience efficient conversion of input voltages to desired negative levels while benefiting from the dynamic buck-boost capability that ensures stability and accuracy, enabling reliable operation across various applications
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Hardware Overview
How does it work?
MCP16331 INV Click is based on the MCP16331, a step-down (buck) switching regulator from Microchip. However, with the help of a few external components, MCP16331 INV Click can regulate voltage levels lower and higher than the input voltage, working as an inverted boost-buck voltage regulator. The MCP16331 INV click is designed to output a negative voltage with respect to the GND. A negative voltage is often used in the analog electronics domain to power up devices requiring both positive and negative voltages. A good example would be an operational amplifier (opamp) which amplifies an AC signal. The signal goes in both positive and negative directions with respect to the GND. Processing this kind of signal using a single voltage source is difficult and requires workarounds such as capacitors, charge pumps, and virtual GNDs. Using a symmetrical power supply reduces the required components and simplifies the design. Several additional components, such as the ADM8828 voltage inverter IC and the LM318, a dual operational amplifier, must be added to deliver a negative voltage. The ADM8828 voltage inverter IC provides a negative component of the symmetrical power supply used for the LM318 dual opamp. One integrated opamp from the LM318 IC is used to invert the output from the DAC.
The other opamp from the LM318 IC is used to invert the output from the voltage divider, located on the output rail of the MCP16331, so that it can be used by the MCU, which uses a single voltage power source. To set the output voltage of the MCP16331 INV click, the MCP4921 - a low-power 12-Bit dual voltage output DAC is used in the feedback loop. As already mentioned, it is necessary to invert this signal as the MCP4921 is supplied from a single-voltage power supply, and it cannot bring the signal lower than the GND. Since MCP16331 works in the negative voltage domain, the feedback voltage applied to the FB pin of this IC also needs to be negative with respect to the GND. One of the LM318's integrated opamps, configured as a unity gain inverter, is used to invert the DAC output voltage. Since the DAC drives the FB pin of the MCP16331 IC, it is enough to set the DAC to a specific value to control the output voltage of the click board™. Communication with the MCP4921 DAC is done via the SPI interface. SPI bus pins of the MCP4921 are routed to the mikroBUS™ for an easy and secure connection with the host MCU. The AN pin of the mikroBUS™ is routed to a middle point of a voltage divider at the output. This voltage divider is used to scale down the output voltage so the ADC of the host MCU can successfully convert it.
The voltage on the divider also has to be inverted since it is coming out from the negative voltage domain. This is achieved by the second operational amplifier of the LM318 IC, which also works as a unity gain inverter. This value can be used to monitor and correct the output voltage if needed. The EN pin of the MCP16331 switching regulator is routed to the mikroBUS™ RST pin. By pulling this pin to a HIGH logic level, the internal sections of the regulator are enabled. The EN pin is internally pulled to a HIGH logic level, so the device will be enabled, even if this pin is left floating. Therefore, a correct startup sequence must be used to avoid undesirable effects (in the NOTE below). Although it is designed to work as the negative power supply, the MCP16331INV click can also be used to drive a regular load, connecting its positive input terminal to the GND of the click board™ and using the negative output of the MCP16331INV click as the GND. MCP16331 INV Click with two screw terminals to connect the input and the output voltage rails. This click board™ uses only +5V rail from the mikroBUS™. Provided libraries demonstrate the functionality of the MCP16331 INV click and offer an easy and simple way of setting it up.
Features overview
Development board
Nucleo-64 with STM32L073RZ MCU offers a cost-effective and adaptable platform for developers to explore new ideas and prototype their designs. This board harnesses the versatility of the STM32 microcontroller, enabling users to select the optimal balance of performance and power consumption for their projects. It accommodates the STM32 microcontroller in the LQFP64 package and includes essential components such as a user LED, which doubles as an ARDUINO® signal, alongside user and reset push-buttons, and a 32.768kHz crystal oscillator for precise timing operations. Designed with expansion and flexibility in mind, the Nucleo-64 board features an ARDUINO® Uno V3 expansion connector and ST morpho extension pin
headers, granting complete access to the STM32's I/Os for comprehensive project integration. Power supply options are adaptable, supporting ST-LINK USB VBUS or external power sources, ensuring adaptability in various development environments. The board also has an on-board ST-LINK debugger/programmer with USB re-enumeration capability, simplifying the programming and debugging process. Moreover, the board is designed to simplify advanced development with its external SMPS for efficient Vcore logic supply, support for USB Device full speed or USB SNK/UFP full speed, and built-in cryptographic features, enhancing both the power efficiency and security of projects. Additional connectivity is
provided through dedicated connectors for external SMPS experimentation, a USB connector for the ST-LINK, and a MIPI® debug connector, expanding the possibilities for hardware interfacing and experimentation. Developers will find extensive support through comprehensive free software libraries and examples, courtesy of the STM32Cube MCU Package. This, combined with compatibility with a wide array of Integrated Development Environments (IDEs), including IAR Embedded Workbench®, MDK-ARM, and STM32CubeIDE, ensures a smooth and efficient development experience, allowing users to fully leverage the capabilities of the Nucleo-64 board in their projects.
Microcontroller Overview
MCU Card / MCU
Architecture
ARM Cortex-M0
MCU Memory (KB)
192
Silicon Vendor
STMicroelectronics
Pin count
64
RAM (Bytes)
20480
You complete me!
Accessories
Click Shield for Nucleo-64 comes equipped with two proprietary mikroBUS™ sockets, allowing all the Click board™ devices to be interfaced with the STM32 Nucleo-64 board with no effort. This way, Mikroe allows its users to add any functionality from our ever-growing range of Click boards™, such as WiFi, GSM, GPS, Bluetooth, ZigBee, environmental sensors, LEDs, speech recognition, motor control, movement sensors, and many more. More than 1537 Click boards™, which can be stacked and integrated, are at your disposal. The STM32 Nucleo-64 boards are based on the microcontrollers in 64-pin packages, a 32-bit MCU with an ARM Cortex M4 processor operating at 84MHz, 512Kb Flash, and 96KB SRAM, divided into two regions where the top section represents the ST-Link/V2 debugger and programmer while the bottom section of the board is an actual development board. These boards are controlled and powered conveniently through a USB connection to program and efficiently debug the Nucleo-64 board out of the box, with an additional USB cable connected to the USB mini port on the board. Most of the STM32 microcontroller pins are brought to the IO pins on the left and right edge of the board, which are then connected to two existing mikroBUS™ sockets. This Click Shield also has several switches that perform functions such as selecting the logic levels of analog signals on mikroBUS™ sockets and selecting logic voltage levels of the mikroBUS™ sockets themselves. Besides, the user is offered the possibility of using any Click board™ with the help of existing bidirectional level-shifting voltage translators, regardless of whether the Click board™ operates at a 3.3V or 5V logic voltage level. Once you connect the STM32 Nucleo-64 board with our Click Shield for Nucleo-64, you can access hundreds of Click boards™, working with 3.3V or 5V logic voltage levels.
Used MCU Pins
mikroBUS™ mapper
Take a closer look
Click board™ Schematic
Step by step
Project assembly
Start by selecting your development board and Click board™. Begin with the Nucleo-64 with STM32L073RZ MCU as your development board.
Track your results in real time
Application Output
1. Application Output - In Debug mode, the 'Application Output' window enables real-time data monitoring, offering direct insight into execution results. Ensure proper data display by configuring the environment correctly using the provided tutorial.
2. UART Terminal - Use the UART Terminal to monitor data transmission via a USB to UART converter, allowing direct communication between the Click board™ and your development system. Configure the baud rate and other serial settings according to your project's requirements to ensure proper functionality. For step-by-step setup instructions, refer to the provided tutorial.
3. Plot Output - The Plot feature offers a powerful way to visualize real-time sensor data, enabling trend analysis, debugging, and comparison of multiple data points. To set it up correctly, follow the provided tutorial, which includes a step-by-step example of using the Plot feature to display Click board™ readings. To use the Plot feature in your code, use the function: plot(*insert_graph_name*, variable_name);. This is a general format, and it is up to the user to replace 'insert_graph_name' with the actual graph name and 'variable_name' with the parameter to be displayed.
Software Support
Library Description
This library contains API for MCP16331 INV Click driver.
Key functions:
mcp16331inv_enable_vin- This function enables or disables internal VIN pull upmcp16331inv_set_dac_vout- This function determines DAC output voltage valuemcp16331inv_generic_transfer- Generic SPI transfer, for sending and receiving packages
Open Source
Code example
The complete application code and a ready-to-use project are available through the NECTO Studio Package Manager for direct installation in the NECTO Studio. The application code can also be found on the MIKROE GitHub account.
/*!
* \file
* \brief Mcp16331Inv Click example
*
* # Description
* This application enables usage of this click as a buck-boost voltage regulator.
*
* The demo application is composed of two sections :
*
* ## Application Init
* Initializes click driver and enables VIN Pull Up.
*
* ## Application Task
* Sets DAC output voltage on 3500mV, when gain is set up on 1x VREF,
* on 4s delay time, and then sets DAC output voltage on 5000mV, when gain is now set up on 2x VREF,
* on also 4s delay time. VIN Pull Up voltage must be greater than 4V.
*
*
* \author MikroE Team
*
*/
// ------------------------------------------------------------------- INCLUDES
#include "board.h"
#include "log.h"
#include "mcp16331inv.h"
// ------------------------------------------------------------------ VARIABLES
static mcp16331inv_t mcp16331inv;
static log_t logger;
// ------------------------------------------------------ APPLICATION FUNCTIONS
void application_init ( void )
{
log_cfg_t log_cfg;
mcp16331inv_cfg_t cfg;
/**
* 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.
mcp16331inv_cfg_setup( &cfg );
MCP16331INV_MAP_MIKROBUS( cfg, MIKROBUS_1 );
Delay_ms( 100 );
mcp16331inv_init( &mcp16331inv, &cfg );
Delay_ms( 100 );
mcp16331inv_enable_vin( &mcp16331inv, MCP16331INV_ENABLE_VIN_PULL_UP );
}
void application_task ( void )
{
// Task implementation.
mcp16331inv_set_dac_vout( &mcp16331inv, MCP16331INV_3500_MV_1X_GAIN, MCP16331INV_GAIN_1X_VREF, MCP16331INV_ACTIVE_MODE );
Delay_ms( 4000 );
mcp16331inv_set_dac_vout( &mcp16331inv, MCP16331INV_5000_MV_2X_GAIN, MCP16331INV_GAIN_2X_VREF, MCP16331INV_ACTIVE_MODE );
Delay_ms( 4000 );
}
void main ( void )
{
application_init( );
for ( ; ; )
{
application_task( );
}
}
// ------------------------------------------------------------------------ END
