STM32L053C8 Questions on power schematic

Question

I am developing a low power board using the STM32L053C8T6TR and have written a schematic to power the board with a 3V coin cell battery and have a few questions.

The datasheet mentions N x 100nf + 1 x 10uF caps on VDD, VSS and while looking at the discovery board schematic, I replicated and came up with the following

In addition to that, the schematic shows the following. Based on the DS STM32 Getting Started I have the following

My question, I am trying to power the board primarily through a coin cell at 3V with the ability to run power through USB if needed while programming (If not using the STLink SWD breakout) Based on the schematics and documentation, I am not really able to tell if I am using too many caps around the LDO, and around the bead between VDD-VDDA. The documentation states N * 100nF + 1 10nF. What is the optimal capacitance and number of caps needed on the 5V input side, and on the output side?

Same goes for the VDD-VDDA capacitors and bead. Am I over subscribing capacitance for a 3V coin cell?

Edit: After looking through some more schematics and datasheets, i'm not even sure there needs to be caps between VDD-VDDA with the bead. Most schematics I see only have the bead. Since this is going to be a super low power dev board working on a coin cell, is all that needed?

Edit: Edited the question to focus on power input and capacitance around the LDO and VDD-VDDA

Answer 1

Ok, Your missing the STM32 schematic itself, to verify everything, we need that.

Next, are you planning on being primarily battery powered? If so, lose the TLC5940! If your just wanting to have a few LED available, just drive them from the STM32, if your concerned about using too many pins, have a look at Charlieplexing.

TLC5940: First off, this thing is a beast! Unless you need ALL of the bells and whistles it offers, I would start off with something easier, like the TLC59108 or the TLC59116.
Most likely you meant it as a decoupling cap, but that 0.1uF in the VCC line needs to be changed. Next, how are you planning on programming it? You need SCLK, SIN, XLAT connected to program it.

The power, SWD, and USB(What type of interface are you using for the USB renum?) all look OK. Oh, BTW, you can reduce the 100uF decoupling caps down to about 40uF, since your battery powered. I can't remember the exact App Note, but ST does talk about it.

I've never used that BT module before, sorry. But there seems to be a slight confusion to my eyes. It looks like your connecting SPI to the BT module, but that EEPROM is also SPI, and there are no active Chip Selects. As it is it looks like you'll talk to both at the same time....

Answer 2

N x 100nf + 1 x 10uF caps on VDD

1. Not really mandatory.
2. Please provide provisions for the caps but do not mount all the 10uF capacitors.
3. Wait for the feedback from lab testing and EMI EMC testing.
4. You do not need a ferrite on the VDDA line if your product does not need such a noise isolation. (for example: if it is a simple NTC reading for temperature)
5. Follow the datasheet recommendation for the LDO capacitors
6. Since it is battery powered, there is no noise on the VIN as such
7. Every capacitor extra you add is a leakage path to ground. Please provide option in the PCB but experiment later for the best possible least possible option. I am not awre about the whole application(RF, Motor or others)
8. Consider adding safety diodes for reverse voltage protection (a PMOS in series with VBAT provides both reverse voltage protection as well as lest drop across it unlike a diode