DRV8305: Inputs the output of the differential amplifier circuit to the Current amplifier negative input (SNx)

Hiroki Sakaguchi

Part Number: DRV8305

Tool/software:

Hello.

I am looking to use the DRV8305 to detect the inline current of a motor.
However, I am aware that the DRV8305 is a low side shunt current sensing and the Current amplifier positive input (SPx) must be grounded.
Therefore, I am considering leaving the Current amplifier positive input (SPx) grounded and introducing the voltage across the inline shunt resistor into the Current amplifier negative input (SNx) through a differential amplifier circuit to detect the current (see attached figure).
Although irregular, is this feasible?

Please let me know.

3 months ago

0 Joshua Maize 3 months ago

TI__Genius 12231 points

Hi Hiroki,

This is an interesting design but I would caution against this roundabout method, as there is a lot of potential for noise to degrade the reliability of the current sensing as trace lengths, the differential amplifier, and passive components in this system may affect the signal quality/accuracy before even reaching the internal CSA amplification.

Is there a specific need to use inline current sensing instead of lowside shunt? (Which is ny recommendation)

Best Regards,

-Joshua

0 Hiroki Sakaguchi 3 months ago in reply to Joshua Maize

Prodigy 170 points

Hi Joshua,

I would like to use this driver to implement a 180-degree energized sinusoidal control scheme for motors.
I believe that inline current detection is necessary because this method has a mode of regenerative operation with only high-side FETs, and there will be a time period when the low-side cannot be detected.
If this method is feasible with a low-side shunt, could you please let us know?

Best Regards,

Hiroki

0 Joshua Maize 3 months ago in reply to Hiroki Sakaguchi

TI__Genius 12231 points

Hi Hiroki,

Thank you for the explanation. I am familiarizing myself with this methodology, but currently am not aware of the necessity to do high-side only braking. For this algorithm is it possible to do low-side braking (all 3 low-side FETs are ON) as discussed in this E2E thread here? -- https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1069426/drv8312-what-s-regenerative-braking

Best Regards,

-Joshua

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DRV8305: Inputs the output of the differential amplifier circuit to the Current amplifier negative input (SNx)