DRV8412 Sense resistor current

Hi SG

If 24V 350mA motor, we can use many other DRV8x solutions. Such as DRV8881 E or P for two BDC. Or DRV8801 for one BDC. Any special reason to use DRV8412?

If only for BDC control, we can only use one shunt R for one H bridge.

Best regards,

Hi SG,

(1) I am driving DC brushed motor in forward direction -I am seeing PWM signal on PWMA and nothing on PWMB as expected. Why do i measure current passing through both sense resistor mean resistor R52 and R53?

You should see current through both sense resistors. The existence of the current depends on the current regulation. Assuming A is PWMed high then low (slow decay or brake mode), current will flow through R52 from OUTB to GND when OUTA is high. When OUTA is low, the current is re-circulated through the winding, and current should be measured through both resistors R52 and R53.

(2) I am using very small motor -24V- 0.35 Amp (max) current and my driving current is 25mA to 70 mA. It seems to me there is not enough resolution for AD output to servo on close loop current control. Do i have to change gain of OpAmp designated OA2 on board ? Any insight/suggestions will be helpful.

Yes, you may have to change the gain. The gain was set to allow maximum currents of the DRV8412.

Hello Rick,

Thank you for clarification on both issues.

In order to change gain I have two options.

Option1: Increase R2 to 10X which will be 226K and also change R3 10X to 340K- This will give me approx 10X better resolutions.

Option2: Reduce R1 by 10X which will be 100 ohm and Change R3 to 295K-This will also give me approx 10X better resolutions.

Can you please advise which one is better options? 10X is desirable but any improvement is acceptable.

Thank you very much for your support.

SG

Hello Wilson,
Thank you for your suggestions.
I am using DRV8412 for current control and also has built in OpAmp. Also DRV8412 Kits comes with right kind of Plug in F28035 processor board and provide an option to control stepper motor. There is also 2XDC motor and Stepper motor example that exactly is my need. I look into DRV8881 and DRV8801. It does has sense resistors but not sure how to build close loop on current using 2XDC Motor example without spending lot of time.
It will be nice if you guys can extend help on how to increase 10X gain of Opamp that will be a great help.
Thank you,
SG

Hi SG,

Option 1 seems to be the preferred approach.

Another approach is to change the shunt resistors if possible. A .25 Ohm resistor increases the gain by 25x.