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Development Board for the STM32F042

Development Board for the STM32F042

Schematic



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The schematic is rather modular so let’s take a look at each section in detail.

The power supply

The 3.3V voltage for the board is supplied by a Texas Instruments LMR10515 adjustable switching buck (step-down) regulator. I’ve used this regulator a few times before and have found it to be a solid and reliable device that doesn’t require many external components and only costs about 50 pence from Farnell.



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This regulator is capable of supplying up to 1.5A with an efficiency level of over 90% throughout most of its range. The input will be the 5V VBUS line from the USB plug after I’ve sanitised it to remove the gremlins that lurk therein.

It’s this efficiency level that allows switching regulators to deliver their peak current rating without burning up in a puff of smoke. The output inductor and schottky diode must both be chosen to match the desired peak current from the regulator. For the inductor I’ve chosen the Murata LQH44PN3R3MP0L (2.1A maximum current) and for the schottky I’m using an ST Micro STPS0520Z (0.5A maximum current).

In practice this means that my development board is limited to 500mA but you can use any schottky that will fit the SOD-123 footprint if you need a higher current supply up to the 1.5A maximum that the regulator can deliver.

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