Author Topic: MOS blows up on a stepper driver  (Read 210 times)

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Offline Yaroooo

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MOS blows up on a stepper driver
« on: April 20, 2021, 08:55:04 am »
Hello guys, I've a problem with a custom board. This board is a power side of a motor power circuit controlled by a logic side that just send configurations, clock, dir, step to a driver controller.

I post here a schematic:

There's also several checks by driver component about overcurrent, overtemperature etc. and another current sens that is controlled by logic side.
This schematics were used on different boards and never fault (but never checked if really correct, maybe fortunate circumstances). I've upgraded MOS with minor changes and now they blow up after some minutes of running, even without load on stepper. Also temperature is low, so it's not related to overheat.

Have I missed something or is there something not correctly sized?
« Last Edit: April 21, 2021, 03:12:35 pm by Yaroooo »
 

Offline Wolfram

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Re: MOS blows up on a stepper driver
« Reply #1 on: April 20, 2021, 10:35:02 am »
Check the HIN/LIN waveforms for overlap. The IR2181 does not have overlap protection, and your discrete PNP inverter will probably have asymmetrical propagation delay due to saturation of the transistor. This can lead to conduction overlap, with high shoot-through currents and potentially also high voltage spikes across MOSFET Vds if your switching loop is underdamped. Ideally you should have a significant and reasonably well controlled dead-time between turning off one device and turning on the other device in the same bridge, this can be implemented with RC delays + diodes. There are also gate drive ICs available with built-in deadtime generation which can be convenient.

Do you have a screenshot or picture of the layout? In power electronics, layout can easily be as important as the circuit topology itself.

Edit: Do you have decoupling capacitors on Vmot?
 

Offline langwadt

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Re: MOS blows up on a stepper driver
« Reply #2 on: April 20, 2021, 10:47:00 am »
is the IR2181 happy with 12V logic inputs ?
 

Online mikerj

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Re: MOS blows up on a stepper driver
« Reply #3 on: April 20, 2021, 11:55:46 am »
Check the HIN/LIN waveforms for overlap. The IR2181 does not have overlap protection, and your discrete PNP inverter will probably have asymmetrical propagation delay due to saturation of the transistor. This can lead to conduction overlap, with high shoot-through currents and potentially also high voltage spikes across MOSFET Vds if your switching loop is underdamped.

The Trinamic controller implements dead time by measuring the gate voltage of the MOSFET being switched off, and waiting until it hits some threshold before switching on the other transistor.  The OP has added some capacitance to the discrete level converters for the upper transistor gate driver, but lower output goes straight to the external gate driver.  Seems to me that the Trinamic controller will see the lower MOSFET being switched off almost instantly so there must be quite some risk of cross conduction.
 

Online jmelson

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Re: MOS blows up on a stepper driver
« Reply #4 on: April 20, 2021, 04:27:59 pm »
I don't see any diodes to protect the common terminal (that connects to high-side source and low-side drain) from being driven below ground.  Do NOT depend on the body diodes in the FETs to protect from this, they often take tens of us to turn on.  I use a similar layout for a brush motor drive, and had to add ultra-fast power diodes across the low-side FET to prevent this.  When the comon terminal goes about 6 V below ground, both outputs turn on at the same time, generally blowing out the FETs.

Jon
 


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