DRV8711 Raise current to 1A

Esme Liu

Intellectual 335 points

Other Parts Discussed in Thread: DRV8711

Hi,

I'm using DRV8711, 1/64 micro step and I want to raise the current to 1A

here is the equation in the drv8711 manual,

I = (2.75V * TORQUE) / (256 * ISGAIN *RISENSE) = 1A

I tried several combination of isgain and torque:

isgain = 20, torque = 186 (decimal)

isgain = 10, torque = 93 (decimal)

isgain = 5, torque = 47 (decimal)

but the current is still less 0.1A

(I can see the current changes when I use 1/256)

Here're my settings for other registers:

Dtime: 850 ns

SMPLTH: 100us

TOFF: 0X28

TBLANK: 0X00

ABT: DISABLE

TDECAY: 0X14

DECMOD: 101

SDTHR: 0X3C

SDCNT: 00

VDIV:10

OCPTH: 00

OCPDEG:00

TDRIVEN: 11

TDRIVENP: 11

IDRIVEN: 00

IDRIVEP: 00

Also the sense resistance for Boost drv8711 is 0.1 ohms, right?

Since there are two 0.05 ohms resisters in series.

Thanks,

Esme

over 8 years ago

0 Rick Duncan over 8 years ago

TI__Guru** 114905 points

Hi Esme,

How are you measuring the current? Are you using the power supply or a current probe?

The sense resistance is 0.05 Ohms. Each resistor is used for one winding; they are not in series.

0 Esme Liu over 8 years ago in reply to Rick Duncan

Intellectual 335 points

I'm using the power supply.

I just used 0.05 to calculate the torque and changed the settings, it is still less than 0.1 A

0 Rick Duncan over 8 years ago in reply to Esme Liu

TI__Guru** 114905 points

Hi Esme,

The power supply reading does not provide the full story. The current read from the power supply typically varies based on the VM voltage. As VM increases, the current reading of the power supply decreases.

If you do not have a current probe, you can look at the voltage across the sense resistors using a scope to determine if you are achieving the desired current.

The best time to examine this voltage is when one coil has 100% and the other has zero. For 1A you should see ~50mV across the resistor when at full scale.

0 Esme Liu over 8 years ago in reply to Rick Duncan

Intellectual 335 points

Hi Rick,

I tried using current probe, it is 0.1A for 1/64
for 1/256, it is 1A with the same settings.

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DRV8711 Raise current to 1A