MCP236 damaged when turned on/off

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cgirerd
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Joined: Tue Jul 16, 2019 11:09 pm

MCP236 damaged when turned on/off

Post by cgirerd » Wed Feb 05, 2020 6:17 pm

Hi all,

I think I am doing something wrong with some MCP236 controllers, but cannot figure out what, so I would like to ask for your help. I have 3 MCP236, had some issues with 2 of them in the past, and now have an issue with one, for the same reason I think.

My setup is as follows: I have a controller, 2 DC motors (these ones: https://www.pololu.com/product/3497) with encoders (these ones: https://www.pololu.com/product/3499). I have a 2.2 kohms pull-up resistors attached to each encoder channel (2 DC motors with quadrature encoders, so 2 channels, and a total of 4 resistors). Everything is powered by a DC power supply. See the attached picture.

The motors are not used when the issue occurs. The issue seems to happen when turning the controllers on or off (I don't know) a few times. I think there may be something wrong with the way I turn it on or off. To turn it on, I connect the power supply to the controller, with a voltage set to 12V, and the current set to 0A. I then increase the current, and the controllers turn on. To turn it off, I decrease the current to 0A, with the voltage always set to 12V. After turning it on and off a few times, the controller is drawing 0.15A with no red/green light on (so... damaged I guess).

Do you know what mistake I am doing, that causes a damage to the controller?
Best,
Cedric
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Basicmicro Support
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Re: MCP236 damaged when turned on/off

Post by Basicmicro Support » Thu Feb 06, 2020 10:32 am

What are you drviing with the motors?

Unclamped motor regen when using power supplies is our number 1 cause of RMAs.

The motors you have cant possibly damage the controller with current which means it basically has to be a voltage spike problem. Regen spikes with power supplies is the most likely cause. Alternatively there could be something wrong with your power supply. Note that all power stage components on the MCP236 are rated for a minimum of 100v.

Your symptom sounds like the high voltage switching regulator is being damaged. This is rated for 100v. If you were using a battery I would say you were getting an inrush current voltage spike killing the regulator. In that case you would want to add a pre-charge circuit(as simple as a switch and resistor to pre-charge the DC Link caps before connecting main power) but when using a power supply this is unlikely to be a problem. Power supplies dont supply enough current for it to be a problem usually. I'm leaning toward a power supply issue.
Please send the units in and we will repair them and see if we can determine the most likely cause of failure.

cgirerd
Posts: 5
Joined: Tue Jul 16, 2019 11:09 pm

Re: MCP236 damaged when turned on/off

Post by cgirerd » Thu Feb 06, 2020 12:28 pm

Thank you for your fast reply.
I am not driving anything with the motors, they are rotating freely. Also, the motors were not used when the issue happened, I just turned the controller on and off a few times to adjust some settings in BasicmicroMotionStudio - max current the motors can draw (1.6A), set to quadrature encoder. After switching it on and off a few times (I would say 5 times) to adjust these settings, I had the issue described with the controller not switching on and drawing 0.16A.
I am checking the power supply now to see if there are some high voltage spikes when I switch the controller on.

cgirerd
Posts: 5
Joined: Tue Jul 16, 2019 11:09 pm

Re: MCP236 damaged when turned on/off

Post by cgirerd » Thu Feb 06, 2020 12:58 pm

I measured the voltage of the power supply over time when switching the controllers on. I usually initially set the voltage to 12V and current to 0A, and then increase the current to a value that allows both the controller and motors to run without any issue. As I do that, and depending on how fast I increase the current, I have some voltage variations that you can see in the attached picture (I am repeating the process 4 times, with the current from 0A to a high value, and the graph on the attached picture represents the voltage over time). As I increase the current, I think I reach a point where the controller is either lacking voltage or current till I reach a nominal current value. Do you think that could explain the issue?
Maybe I should set the voltage to 12V and current to a high value, and plug the controller directly to the power supply.
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Basicmicro Support
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Re: MCP236 damaged when turned on/off

Post by Basicmicro Support » Fri Feb 07, 2020 10:24 am

Undervoltage shouldnt be able to damage anything. My concern would be a votlage spike but it would have to be over 100v. A negatvie spike(more than approximately -3v would also damage the controller). I dont see either though it would be hard to tell if there is a negative spike on that scope trace.

When you said the motors arent used when the issue happens, did you mean the motors arent attached or just you arent running the motors? Keep in mind the damage could have happened the last time you turned the unit off or while the unit was off(static electricty discharge or backdriving the motors while the power supply is off/disconnected).

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