STM32L031K6 Power Issues SPV1050 (mandatory bulk capacitors)

[DKlin.2]

According to the datasheet a 10uF should be considered at VDD and 1uF at VDDA.

Are these values mandatory for a robust design? I’ve checked various STM32L0 schematics on the internet and most of them use only the 100nF capacitors.

I’m asking this question because I face two issues:

-         The LDO from SPV1050 (energy harvester) collapses when I connect the MC including the 10uF capacitor

-         I have very less space on the PCB, every component I can omit will help

Additional question:

Can I leave the NRST pin floating and skip the capacitor, when I do not need any reset on my PCB? I suppose the MC has internal pull-up.

Thanks a lot for any feedback!

[TDK]

> Are these values mandatory for a robust design?

The caps you highlighted are bulk capacitors. It is generally recommended to have bulk capacitance somewhere on the board, even if the board may work without it. Sometimes there is a bulk capacitance near the LDO supplying the power. If it's close enough to the chip, that can suffice.

The answer is going to be specific to your application, but the recommendation is there for a reason. If it's important enough to you, you can leave them out and test it. I find there are enough things to troubleshoot with boards that adding the cap to eliminate potential issues is usually the correct choice.

> Can I leave the NRST pin floating and skip the capacitor,

No, you can get spurious resets due to the line bouncing. The capacitance stops this from happening. It does have an internal pullup, but noise can cause the line to bounce without any capacitance.

[DKlin.2]

Many thanks for your feedback!

The STM32 is powered by an SPV1050 which has two build in LDOs. My problem is, when the capacitive load is getting greater 4-6uF the voltage on the LDO output collapses after I enable the LDO or won’t even built up.

May someone has experience with the SPV1050 and can give advice?

[TDK]

I would separate the STM32 from the SPV150 in order to debug. It sounds like a hardware issue somewhere. Adding 5uF of capacitance shouldn't affect the LDO. If you don't see 3.3V on that line, it's probably not the fault of the STM32.

[DKlin.2]

Yes, y​ou are correct, it's not the fault of the STM32.

I​'m currently prototyping with the Steval-ISV019V1 (evaluation board for SPV1050) and have only changed the resistor ladder for MPPT. When i connect >4-6uF on the LDO output, the LDO voltage collapses.

​Accually I do not know what i should change at the schematic. All the values seems to be quite standard.

Perhaps i have destroied the LDOs?

Energy harvesting works nice.​