Charge up and be ready with LTC3225 and STM32L496AG

UPS Click is based on the LTC3225, a 150mA supercapacitor charger from Analog Devices, used to charge two serially connected capacitors with a controlled current and constant voltage. The LTC3225 has the unique ability to maintain constant voltage levels on both of the connected supercapacitors by monitoring their voltages. This improves the lifecycle of the supercapacitors, protecting them from overvoltage. When a voltage difference occurs during charging (depending on the dissimilarities between the two used supercapacitors), the voltage across one of them might rise enough to cause damage. Unlike other balancing techniques that use resistors to discharge the capacitor, which has a greater voltage, the LTC3225 automatically adjusts the charging currents of two capacitors until their charging speed is equal. The difference between the charging currents can be increased or decreased by 50%. When the Cout voltage reaches its nominal value (selected by the pull-up resistor on the Vsel pin to 5.3V), the internal charge pump is turned off, allowing the IC to enter the low power mode. The recharging cycle is automatically restarted when the voltage of the supercapacitors drops under a threshold. The output terminals are used to connect an external load. There are two screw terminals routed to the output pins of each capacitor. Two supercapacitors are serially connected: the high-side capacitor has its positive pin connected to the Cout (a regulated voltage output pin),

while the low-side capacitor has its negative pin connected to the GND. The negative pin of the high-side supercapacitor and the positive pin of the low-side supercapacitor are connected together and routed to the CX pin of the LTC3225, which is maintained at Cout/2. Therefore, the voltage across a single terminal is Cout/2, so to use the full range of the output voltage, a load should be connected between the high-side terminal labeled with the “+” sign and the low-side terminal labeled with the “-” sign. These terminals can also be used to connect additional supercapacitors since the supercapacitors are in parallel with the connected load. When the power source is turned off, the output voltage (Cout) depends only on used supercapacitors. These two supercapacitors have an equivalent capacitance of 1.65F, and they will become the only elements that provide power for the connected load when the power supply is removed. According to the capacitor discharging formula, these capacitors will discharge through the connected load, and the output voltage will exponentially decrease. The #SHDN pin can put the device in the low-power shutdown mode by applying a LOW logic level. This pin is routed to the RST pin of the mikroBUS™, labeled as SDN. It is pulled to a HIGH logic level by an onboard pull-up resistor. It is possible to read the output voltage value by using the voltage divider connected between the GND and the Cout. When the supercapacitors are fully charged, with the Cout

voltage level of 5.3V, the value on the middle point of the voltage divider will be about 1.7V. The middle point of the voltage divider is routed to the AN pin of the mikroBUS™, allowing an easy analog-to-digital conversion by the host MCU. This pin is labeled as SEN on the Click board™. The PGOOD pin of LTC3225 IC is routed to the mikroBUS™ CS pin and labeled as PGD. This pin is an open-drain output, and it is pulled to a HIGH logic level by an onboard resistor. When the output voltage reaches a value 6% below the nominal value, this pin is de-asserted. When the voltage drops under 7.2% below its nominal value, this pin is asserted and pulled to a LOW logic level. It can be used to monitor the state of the output supercapacitors. The Click board™ uses a power supply from the mikroBUS™. Moving the onboard SMD jumper labeled JP1 makes it possible to select either a 3.3V or 5V rail as the input power source. It also selects the IC operating voltage, allowing interfacing with both the 5V and 3.3V MCUs. Regardless of the selected operating voltage, the output voltage is always 5.3V, as set by the Vsel pin of the UPS click. UPS click uses only the GPIO pins of the MCU for setting states on its pins; therefore, it is extremely easy to work with. However, the 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.

The 32L496GDISCOVERY Discovery kit serves as a comprehensive demonstration and development platform for the STM32L496AG microcontroller, featuring an Arm® Cortex®-M4 core. Designed for applications that demand a balance of high performance, advanced graphics, and ultra-low power consumption, this kit enables seamless prototyping for a wide range of embedded solutions. With its innovative energy-efficient

architecture, the STM32L496AG integrates extended RAM and the Chrom-ART Accelerator, enhancing graphics performance while maintaining low power consumption. This makes the kit particularly well-suited for applications involving audio processing, graphical user interfaces, and real-time data acquisition, where energy efficiency is a key requirement. For ease of development, the board includes an onboard ST-LINK/V2-1

debugger/programmer, providing a seamless out-of-the-box experience for loading, debugging, and testing applications without requiring additional hardware. The combination of low power features, enhanced memory capabilities, and built-in debugging tools makes the 32L496GDISCOVERY kit an ideal choice for prototyping advanced embedded systems with state-of-the-art energy efficiency.