Introduction
This application note describes the MB1971 X-NUCLEO LLC DC/DC expansion board for converter shield designed specifically
for the STM32F334/STM32G474 Nucleo boards. It is a low-cost and easy-to-use development kit useful to quickly evaluate and
start develop application with the microcontrollers of the STM32F334/STM32G474 series. It plugs directly onto the MORPHO
sockets, adding all the necessary hardware to evaluate the hi-resolution timer for the half-bridge LLC power converters.
The STM32F334 & STM32G474 Arm
®
Cortex
®
-M4 microcontrollers, embedding a hi-resolution timer, combines high integration
and performance. They have been designed for digital power conversion applications. This LLC DC/DC converter board
illustrates how they can control a half-bridge LLC topology on both the primary and secondary side.
This demonstration needs an external 12 V/1.5 A power supply that is connected to the add-on board.
The firmware associated to this example needs to be programmed into your STM32F334/STM32G474 Nucleo board prior to the
demonstration.
Arm is a registered trademark of Arm Limited (or its subsidiaries) in the US and/or elsewhere.
Introduction to MB1971 LLC HAT 12 V to 7.5 V/1 A for F334 G474 Nucleo board
AN5978
Application note
AN5978 - Rev 1 - September 2023
For further information contact your local STMicroelectronics sales office.
www.st.com
1 Application description
1.1 Required hardware
This application uses the STM32F334 or the STM32G474 Nucleo board. An external DC power supply (12 V dc
1.5 A minimum) is required for the demonstration.
The external power supply must be connected to the CN1 or CN2 socket, while the Vout DC voltage is the output
on CN3.
Caution: when connecting an external power supply, make sure that the polarity is correct.
1.2 Overview of the LLC stage
The purpose of this DC/DC stage is to step the 12 V dc input down to a 7.5 V dc output. The general overview of
the LLC half-bridge topology used for this conversion stage is shown in Figure 2. The power stage of the
converter is formed by:
• The input and output capacitors C4 and C9.
• The two MOSFETs Q2 and Q9.
• The transformer T1.
• The inductor L1.
• The resonant capacitors C12, C13, C14, and C15 in parallel.
The resonant inductor Lr and the magnetizing inductor Lm depicted in Figure 2 are integrated into the LLC
transformer as:
Lm = 6.4uH, Lr = 0.3uH.
The extra inductor L1 is used to increase the leakage inductance.
The output rectification stage is implemented with two N channels MOSFETs Q1 and Q11. They are switched
alternatively within each PWM period while the transformer secondary mid tap is connected to the DC output.
AN5978
Application description
AN5978 - Rev 1
page 2/41
