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Problem with burned FETs and drivers after reconnect battery

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CTSchorsch
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Problem with burned FETs and drivers after reconnect battery

Hi all,

i build a custom PCB (https://github.com/CTSchorsch/gesc). Most times, it runs fine. But sometimes i have a problem, i don't find the reason:

- Motor stops, or did not start again after break

- Reset of CPU does not work (disable 3v3)

- Now if i disconnect and reconnect the battery the driver and FETs of minimum one phase blown away...

Has someone an idea what is my mistake ?

Regards and thanks

Georg

skyline1970
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Hi,

You could check after connected 5-10nF capacitors between G and S of mosfets, initially. Or you could test the drive by using just 12V motive power.

High side bypass capacitor values should be higher. (And a parallell tvs (P6KE15) )

At +12V and gnd a TVS 14V could be placed. 

A 10 ohm resistor in series could be insetrted in each boost diode.

HS pin of LM5107, a series 6 ohm resistor could be placed to each phase output. (A resistor 5R6 or 6R8 should be placed between Gate drive SH_x  and Half  bridge mosfet midlle point.)

HS pin of LM5107, and gnd a reverse high-speed schottky diod could be placed. (A schottky diode (3-4A 200V rating) should be placed between Gate drive SH_x and GND, diodes anode at GND.)

 

CTSchorsch
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Hi Skyline,

thanks for your feedback.

- HighSide bypass is easy to change, i will try. Do you think 1u is enough ?

- TVS for the 12V supply is a good idea

- The boost-diode is optional for the LM5109, the LM5107 has an internal one

- Add a resistor in the HS line is not possible in the actual design, i will keep it in mind for the next revision

- The TVS between HS and GND is a very good thing. I measured negative peek at HS line with about -4 to -5V. This is too much for the LM...

Thanks again

Regards

Georg

skyline1970
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22uF/35V recomended, maybe too big.

CTSchorsch
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Hey skyline1970,

a few more questions :)

- high side bypass cap is now 10u/25V. this i allready have in my design. i want to keep the count of different parts low

- JLC has this TVS -> P6SMB15A,  is this fine for parallel to high side bypass ?

- and maybe the P6SMB9.1A for 12V

- do you think it is better to place a TVS between VBAT and GND ? I saw this on some schematics

- schottky for HS Pin I want to use a SS210 (its only 100V and 2A) this should work for 36V VBAT i think

Thanks

Georg

 

 

 

 

skyline1970
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P6SMB15A ok!

For Vbat a few parallel 5KP.. series Tvs would prevent rise on the voltage. Vdr also could be added.

CTSchorsch
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I did some tests with parts i have had here in my boxes:

- Add a 5R6 resistor into the phase connection of the driver, and add a 10u/25v on top of the already places 100nF high side bypass cap

vesc_add_r.jpeg

 

- Add a SS210 schottky diode between Phase and GND

vesc_add_d.jpeg

I did some double pulse tests:

VBat 36V, I=65A

tek00010.png

In my opinion, there are still two spikes that are critical for the driver with negative peaks

rising edge:

tek00011.png

falling edge:

tek00013.png

As i know the FET driver can only handle a few negative Volts. Or do you think this i fine ?

skyline1970
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"a SS210 schottky diode between Phase and GND " not like that. It is important that the diode should be connected near to the driver IC, before the R on the phase. Its purpose to protect the IC itself. Use TVS is also important. At the boost drive voltage pins and whole motive power.

CTSchorsch
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Ok, i move the schottky to the driver :) 

"before the R on the phase" means: between driver pin and r, or between r and phase output ?

I have no TVS on stock, i have to order some. this is the next stepp

CTSchorsch
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Its much better now:

tek00000.png

 

tek00001.png

Thanks Skyline ! I will take further measurements when the TVS diodes arrive.