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
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.)
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
22uF/35V recomended, maybe too big.
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
P6SMB15A ok!
For Vbat a few parallel 5KP.. series Tvs would prevent rise on the voltage. Vdr also could be added.
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
- Add a SS210 schottky diode between Phase and GND
I did some double pulse tests:
VBat 36V, I=65A
In my opinion, there are still two spikes that are critical for the driver with negative peaks
rising edge:
falling edge:
As i know the FET driver can only handle a few negative Volts. Or do you think this i fine ?
"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.
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
Its much better now:
Thanks Skyline ! I will take further measurements when the TVS diodes arrive.