Voltage Stacking with energy harvesting STM32WB55

[methene]

Hello, I am attempting in voltage stacking of 2 STM32WB55 board, but unlike arduino I could not connect Top board's GND to bottom board's 3.3 V pin. I would like to request for help or insights for alternative method I could make it work. I would really appreciate the help. 

Problem

1. When I connect the Top STM32 GND to the VDD of Btm STM32, it discharged the voltage in Btm capacitor.

2. On one attempt I rearranged the circuit in similar stacked configuration, it did not discharged the Btm capacitor voltage. Instead the system goes haywire.

Thank you.

[methene]

Yes I am fully aware the boards are not meant for the purpose of this, is just that my topic are related to voltage stacking of microcontrollers with energy harvesting capabilities. I appreciate any input on how can I make it functionable, but if it is impossible I might have to switch my approach to this.

Thank you very much for you knowledge. Would appreciate if there any other method I could achieve similar result.

[Andrew Neil]

The document you attached showed that this relies on special power supply arrangements within the chip - I really don't think it's something that you can apply to an existing chip or board which does not have that designed-in.

[methene]

Yes the documents I had sent is on the transistor level of voltage stacking, which are more common. My goal is to find out if it is possible for off-chip implementation of voltage stacking, especially energy harvesting voltage stacking. Which I was able to achieve with arduino, and I don't think arduino is made with this intention as well. Hence the obnoxious connection, I know it looks crazy but I was able to achieve halving of current which was a point mentioned for the advantage of voltage stacking. 

If it is really impossible with STM32 board to do that arrangement, I have to revise my research goals and objective. 

[Andrew Neil]

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@methene wrote:

 I was able to achieve halving of current  

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but at the cost of doubling voltage - so no actual gain in power / energy ?

[methene]

Yes, this is the reason I mention Ohm's law, it doubles the voltage by reducing the current, it might not be the correct concept but doubles the V to halve I. In the paper attached below, it did mentioned that there is no actual gain of power/energy. One of the advantage of it is by reducing power through energy leakage, which is one of the reason voltage stacking is used. If ignoring voltage level shifter in stacked configuration, the energy consumed actually reduced.

But for my purpose I am not considering the energy leakage because it is harder to measure the leakage in microcontrollers. Rather I just wanted to find out the halving in current, and mentioned the wear and tear of components. 

[Andrew Neil]

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@methene wrote:

I just wanted to find out the halving in current, and mentioned the wear and tear of components. 

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Current flow (within specifications) does not cause "wear and tear".

Also, you are not halving the current through the two STM32 (or Arduino) boards - each board still draws the same  current.

[methene]

The "wear and tear" do not come from me but I just simply referring to what most other paper are mentioning, maybe there are other components I missed.

In a stacked or non stacked configuration the arduino will be drawing same current, but if I compare non stacked with stacked configuration. The current draw is half in stacked configuration compared to non stacked configuration. 

[Andrew Neil]

But, again, the voltage has to be doubled - so there is no gain in the power/energy used.

[methene]

Yes, you are right, as I had mentioned before, double the voltage halving the current.

There are other advantages such as noise reduction, reduce in energy leakage in other readings. As for my goal, it is to find out if this particular method can be apply to energy harvesting microcontrollers, the rest of the advantages will be handled down the road later. In my case, I am using STM32WB for the implementation.

But my problem here is how can I achieve this particular result with STM32WB55. 

[Uwe Bonnes]

You can not simply stack. What maximum voltage is the PV generator.

Probably above 3.6 Volt. So in full sunshine you will kill the STM32.

Stack the PV Generators, but supply each STM by a fitting voltage regulator. Input of the regulator is top of the PV unit, return is bottom of the PV unit. No direct connection of top return to STM supply below.