Custom board using STM32L053C8T6

[NSoin.1]

Hi All

I am trying to build a custom board (for the first time :)) using an STM32L053C8T6. The board will power an LED and do short burst measurements of its reflection off a strip (< 1s). I am trying to power up the board using a photovoltaic cell and hence I want to minimise the power consumption.

So my questions are:

1. What are the bare minimum components required on the microcontroller PCB for it to function? I have currently put up a SWD connector, USB and XC6206PxxxMR regulator (both of these would be removed in the final iteration to minimise power draw) and corresponding decoupling capacitors and low pass filters for the VDDA. I have a switch for BOOT0. Am I missing anything?
2. I will be using the internal crystal oscillator instead of adding any additional XCs. Is this okay?
3. Looking at the datasheet for the STM32L053C8T6,the low-power series, it does not say anything about pulling down the SWCLK and SWDIO to HIGH and LOW, respectively (which seems to be the case for other STM32 microcontrollers). So there is some confusion on what the state of these lines should be?
4. Put in the 10-pin SWD/JTAG connector but on the STM32L053C8T6 I could not see any pin for the SWO (trace output) which should be on Pin 6 (checked on CubeIDE). However, this is available on the Discovery board.

Many thanks for the help.

Cheers!

[TDK]

> What are the bare minimum components required on the microcontroller PCB for it to function? I have currently put up a SWD connector, USB and XC6206PxxxMR regulator (both of these would be removed in the final iteration to minimise power draw) and corresponding decoupling capacitors and low pass filters for the VDDA. I have a switch for BOOT0. Am I missing anything?

That's about it. If you're not using analog stuff, or even if you are and can live with slightly worse performance, just tie VDDA to VDD directly. Bulk capacitors are also needed. 0.1uF capacitor on NRST.

> I will be using the internal crystal oscillator instead of adding any additional XCs. Is this okay?

Yes. This chip supports crystal-less USB.

> Looking at the datasheet for the STM32L053C8T6,the low-power series, it does not say anything about pulling down the SWCLK and SWDIO to HIGH and LOW, respectively (which seems to be the case for other STM32 microcontrollers). So there is some confusion on what the state of these lines should be?

You don't need external resistors on these lines. The programmer-side will have them if needed.

> Put in the 10-pin SWD/JTAG connector but on the STM32L053C8T6 I could not see any pin for the SWO (trace output) which should be on Pin 6 (checked on CubeIDE). However, this is available on the Discovery board.

This chip doesn't have an SWO pin. It's optional.

The SWO is on the st-link portion of the discover board but it's not connected to the target chip.

[NSoin.1]

Ah that's great and thanks for your quick reply.

I have some analog devices sitting separately on an another board in case I manage to fry up things! But other than that fingers crossed!!

Once again, many thanks

[TDK]

Good luck! Making boards has always been the funnest part of the project for me.

[NSoin.1]

One last question if I may.

Looking at the  AN4879 application note on hardware and PCB guidelines, sec. 2.4 says, "The USB data stream itself (SOF signalization), no external resonator/ crystal is needed (this feature is only available for devices embedding a crystal-less USB 2.0 FS device interface)".

Does that mean that I cannot use the internal oscillator unless I am using a USB connection all the time and the board cannot be used in a stand-alone mode?

Thanks

[TDK]

You do not need to use USB in order to use the HSI.

[NSoin.1]

Thanks a lot 🙂