MC33771C overcurrent protection in normal mode

[tbondar]

I am trying to implement overcurrent protection using MC33771C. This is my understanding of how it is supposed to work. Please let me know if this is the right approach at all or I'm getting it wrong.

1. I use the chip in normal mode and configure cyclic measurements with SYS_CFG1[CYCLIC_TIMER].
2. The chip continuosly measures Isense input and if the measured value increases a threshold it activates it's FAULT pin
3. The activated FAULT pin triggers a GPIO interrupt of the connected MCU which turns the load off the prevent damage in case of high current.

Regarding setting the current threshold, I'm concerned that the datasheet says:

"Registers TH_ISENSE_OC contains the programmed overcurrent threshold in sleep mode."

Does this feature work in normal mode as well? If it does which register to set for normal mode? Or, is this just a documentation error?

[tbondar]

Hi Rafa, thanks for your answer. Basically I have to poll the chip via SPI, so my response time can't be much better than a few milliseconds. Considering the MCU needs to do other things as well, this might be in the range of a few tens of ms. This might be too slow for overcurrent or short circuit detection. I'm wondering how do people solve this in their design?

I'm also curious what is behind the design decision of not supporting overcurrent detection in normal mode, when over and under voltage detection is available?

[RafaR]

Hello tbondar

I'm sorry, but I don't know the specific reason behind this decision to only allow overcurrent detection in sleep mode.

It was a decision made by the designers, one of the reasons that could be behind it would be the consumption levels of the device in normal and sleep mode.

Overvoltage /under voltage detection can be used in both modes, that feature is not limited to one mode, in case you are interested, overtemperature /undertemperature detection is not limited to one mode either.

I hope this information has helped you, please let me know if you need help with anything else.

Have a great day and best of luck.

[RafaR · Accepted solution]

Hello tbondar

Good day!

Your approach is correct but unfortunately it is true that this option is only valid for sleep mode.

The TH_ISENSE_OC register is specifically used for overcurrent detection in sleep mode.

In normal mode, this register does not apply, and overcurrent protection must be implemented externally by the MCU using the measured ISENSE values.

One option would be to continuously read the ISENSE measurement via SPI or TPL.

Please take a look at the chapter. 9.8.6 GPIO5, GPIO6 used as ISENSE

I hope this information has helped you, please let me know if you need help with anything else.

Have a great day and best of luck.