MCF8329A: How do I calculate the q-Axis current?

?? ?

Prodigy 70 points

Part Number: MCF8329A

Tool/software:

Hello, I'm currently measuring the current of a motor and am facing a few challenges.

I measured the DC current using BUS_CURRENT at 0x40E and was able to calculate it using the equation provided in the datasheet: 'IBus = (BUS_CURRENT / 227) * Base_Current/(2CSA_GAIN_FEEDBACK)'. However, I'm confused because the Base_Current in this equation seems different from the BASE_CURRENT I set at 0xAE. Based on my assumption, I've been using the value before multiplying by 32768 / 1200, but is this correct?
To measure the q-axis current, I read the value at 0x4DE. However, the equation doesn't seem to match at all in this case. The measured value mostly stays around 0xFExxxxxx. While I may need to check if there's a circuit issue, is it normal to see such values?

Thank you for your continued help. Have a great day!

10 months ago

+1 Sachin S 10 months ago

TI__Expert 6011 points

Hi,

Thanks for your question, the register values are signed HEX numbers, please take a 2's complement to get the magnitude of the current values, then convert it into the actual value using the formula.

Thanks and regards,

Sachin S

0 ?? ? 10 months ago in reply to Sachin S

Prodigy 70 points

Thank you. Upon checking, I found that there was an issue in the casting process.
Is it normal that the bus current is not measured at all in both the idle state and open-loop state?

0 Sachin S 10 months ago in reply to ?? ?

TI__Expert 6011 points

Do you mean the register outputs a zero when you say "is not measured at all"

0 ?? ? 10 months ago in reply to Sachin S

Prodigy 70 points

Yes, I found that DC current is not being measured during the initial MSS stage when a speed command is given. However, I noticed that it is measured correctly in the closed-loop stage.

+1 Sachin S 10 months ago in reply to ?? ?

TI__Expert 6011 points

Hi,

The BUS_CURRENT values are estimated by the algorithm only in closed loop.

Thanks and regards,

Sachin S

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MCF8329A: How do I calculate the q-Axis current?