INA240: BLDC Motor Inline current sense for different GND

user6262852

Part Number: INA240

Hi, I use the INA240 for inline current measurement for motor application. The coil (MPZ2012S601) is located between the ground of the INA240 and the ground of the motor (BLDC). Is it a problem if it is not on the same ground line for current measurement ? Thanks in advance.

over 4 years ago

0 Guang Zhou over 4 years ago

TI__Mastermind 27380 points

Hi,

This grounding arrangement is not a problem.

There will be a slight voltage difference between the battery ground and signal ground due to coil impedance. But this shouldn’t pose issue to the measurement.

Regards, Guang

0 user6262852 over 4 years ago in reply to Guang Zhou

Prodigy 90 points

Hi,

Thank you for answer. In addition, I want to use common mode choke instead of L6. Would there be any problem in this case?

Regards, Halis

0 Guang Zhou over 4 years ago in reply to user6262852

TI__Mastermind 27380 points

Hi Halis,

Typically the common mode choke effective frequency range is many times that of INA240 working frequency, it shouldn’t affect its normal operation.

In this schematic, input bias current of INA240 is taken directly from battery, bypassing choke and returned to battery through L6 and L8. The choke doesn’t see a pure differential signal. However, since it is a DC current, the common mode choke shouldn’t have any negative effect.

Regards, Guang

0 user6262852 over 4 years ago in reply to Guang Zhou

Prodigy 90 points

Hi Guang,

I have one more question. I need 2nd order low pass filter for INA output without using an extra opamp, is it possible ? Thanks.

Regards, Halis.

0 Guang Zhou over 4 years ago in reply to user6262852

TI__Mastermind 27380 points

Hi Halis,

Yes it is possible to have a second order passive LPF at the output, consisting of a cascade of two RC filters.

Regards, Guang

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INA240: BLDC Motor Inline current sense for different GND