LV8729V with STM32

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sigi
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Joined: Mon Sep 28, 2020 3:17 pm

LV8729V with STM32

Post by sigi »

Hi Im using a LV8729 @ 28V with a STM32 pins connected directly to the inputs of the LV8729 (no resistors or anything else) and of course I burn several STM32 units from Robotdyn... it hurts! And yes I need the 28V for hi speed on a big Telescope control...

My question is Do I need to use opto couplers to stop burning MCUs or it is just the lack of resistors the problem???

Using a new MCU the system works for a while then the MCU starts heating up and die, maybe it is a high drain current sucked by the LV8729 inputs or very high voltages pulsed from the motor driver to that attacks the MCU pins...

I know that LV8729 @12V can be used with normal 5V arduinos directly without resistors by the design used here https://blog.protoneer.co.nz/wp-content ... matics.png

stevestrong
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Re: LV8729V with STM32

Post by stevestrong »

And where is your schematic?

sigi
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Re: LV8729V with STM32

Post by sigi »


stevestrong
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Re: LV8729V with STM32

Post by stevestrong »

I cannot detect any Vdd pin in LV8729V datasheet. Which pin do you mean instead?
Hopefully not Vreg1, because it is 5V output, which will fry the STM chip very quickly if connected to 3.3V (according to your schematic).

And I cannot see any link between the GNDs to STM.

sigi
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Joined: Mon Sep 28, 2020 3:17 pm

Re: LV8729V with STM32

Post by sigi »

well I start using the info on this page:
https://wiki.fysetc.com/LV8729_V1.0/

here is the complete drawing...
https://mega.nz/file/VPACmDYR#XC4JSNDjM ... jFj0ESoaTs

To shut down the system I just cut the ground so the connector to do that... grounds are all connected. The system uses 12v/28v power supply.
I try moving the Vdd of the LV8729s to the AMS1117 output but the result was the same, a little better life duration to be honest.

stevestrong
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Re: LV8729V with STM32

Post by stevestrong »

You are not allowed to connect all grounds together. The motor GND should be separated from the rest, as depicted in you attached link.
Digital supply must be separated from the motor supply, too.

On those modules (4 layer board!) there are some electronic components which we don't know, so untill you get that schematic I cannot tell you more about that.

sigi
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Joined: Mon Sep 28, 2020 3:17 pm

Re: LV8729V with STM32

Post by sigi »

so the ground is what kills the MCU?
It is relatively simple to isolate the Motor ground but if I dont share the logic ground with the MCU the signal do not work.

In the other hand if I isolate the MCU with optos the ground of the motor can not be shared with the optos secondary part?

For example these TB6560 modules use optos to isolate the MCU, but the logic in the other side of the optos and the motor share the ground...
https://www.ebay.com/itm/TB6560-3A-Step ... SwTj9fJ7Iy

stevestrong
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Re: LV8729V with STM32

Post by stevestrong »

You should connect the GND of motor control logic and MCU, but not to the motor supply.

I do not think that you need optocouplers, but I am not 100% sure because the schematic of the LV8729 module is not known.

I would connect the MCU to the module pin by pin and than verify when it starts to heat up.

sigi
Posts: 28
Joined: Mon Sep 28, 2020 3:17 pm

Re: LV8729V with STM32

Post by sigi »

thanks...
so as long as I do not connect motor ground with logic ground maybe it will be ok? On a second review of the first pdf that I refer to it is CLEAR that logic and motor power supply can NOT be the same (line & ground). :oops:

I will re read the datasheet to see if there is any mention about isolation from logic to power parts... thanks. It seems logic to me now. :D

I suppose that I can use a DC-DC 1:1 small isolated converter to measure the 28v motor voltage with the MCU... similar to this: https://www.ebay.com/itm/Mornsun-B1205S ... Sw37BaTxs-

stevestrong
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Re: LV8729V with STM32

Post by stevestrong »

sigi wrote:
Tue Nov 24, 2020 12:34 am
I suppose that I can use a DC-DC 1:1 small isolated converter to measure the 28v motor voltage with the MCU... similar to this: https://www.ebay.com/itm/Mornsun-B1205S ... Sw37BaTxs-
I don't think so. That converter is a power converter which outputs constant 5V.
You should search for something like this: https://electronics.stackexchange.com/q ... lly-isolat

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