DRV8711: about distortion of current waveform

Kei.Sugimoto

Part Number: DRV8711
Other Parts Discussed in Thread: , CSD88537ND

I try to adjust current waveform referring to document SLVA637.
(DRV8711 Decay Mode Setting Optimization).

I think my case is similar to current distortion pattern 5 (p.11).
So I changed the parameter TOFF first.
But I can never resolve distortion at zero cross.

"please see the atatteched captures."

What is the cause of in this case?
Is there any point to check?

Test conditions: VM=24V, Itorque=1.4A Micro-step=1/128

DECMOD 101 All AutoMixed decay
TBLANK 2.56us
ABT On
TDECAY 4us
TOFF 1us

Best regards
Kei.Sugimoto

over 7 years ago

0 Rick Duncan over 7 years ago

TI__Guru** 114905 points

Hi Sugimoto-san,

What is the sense resistor value used?
What is the TORQUE setting?

0 Kei.Sugimoto over 7 years ago in reply to Rick Duncan

Prodigy 60 points

Hello Rick-san.
Thank you for replying quickly.

>What is the sense resistor value used?

I use it 0.05Ω same as Evaluate board BOOST-DRV8711.　

>What is the TORQUE setting?

TORQUE register setting is 17h 20h.
And ISGAIN set 5 as default.
Therefore I calculated Ifs was 1.375A.
It was 1.41 by real measurement.

Perhaps signal waveform is depend on characteristic of motor.
I write relevant parameters below.

VM :24V
Qg :14nC　　 (using CSD88537ND)
RDS :12.5mΩ (using CSD88537ND)
RL :5.4Ω/phase
LL :2.9mH/phase
CL :unknown
θ　 :1.8/step
IL :1.0A/phase
Rsense:0.05Ω
nm :128step

Best regards
Kei.Sugimoto

0 Rick Duncan over 7 years ago in reply to Kei.Sugimoto

TI__Guru** 114905 points

Hi Sugimoto-san,

Many of the lower steps are within the offset voltage of the amplifier. Increasing the sense resistor should help.

Please try adjusting your sense resistor to .3 or .33 Ohms. Reducing the blanking time to 1us may also help.

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DRV8711: about distortion of current waveform