DRV2605L: PWM Driving Open Loop Vs. Closed Loop

greeneyehawk

Part Number: DRV2605L

Hi,

Testing a few LRAs--using autocalibration before driving with PWM signals with bidirectional input set on the DRV2605L.

When using PWM to drive an LRA motor in Open Loop, a 50% duty cycle at 128 * frequency_of_lra gives 0 vibration as expected.

If I change over to closed loop, a 50% duty cycle makes the LRA vibrate erratically and softly. Do I need to adjust my pwm driving frequency depending on what the autoresonance feature finds as the desired frequency? Or should a 50% duty cycle mean no output no matter what?

Any help would be greatly appreciated!

over 2 years ago

0 Christine Lambert over 2 years ago

TI__Prodigy 440 points

Hello!

When you are in closed loop, what effects the duty cycle is the BIDIR_INPUT register. When BIDIR_INPUT = 0, then the duty cycle will be zero so there will be no vibration. When BIDIR_INPUT =1, then the duty cycle is 50%.

In the datasheet, you can find more information on this on pages 31 and 32.

Best,

Christine

0 greeneyehawk over 2 years ago in reply to Christine Lambert

Prodigy 30 points

Hi Christine,

Thanks for the reply.

I keep BIDIR_INPUT=1, so I expect no vibration at 50% duty cycle. I get no vibration in open loop mode. When I switch to closed loop still at 50% duty cycle, I get small vibrations that don't seem consistent.

Best

0 Christine Lambert over 2 years ago in reply to greeneyehawk

TI__Prodigy 440 points

Hi again,

You should expect no vibration when BIDIR_INPUT= 0 when in closed loop. This is when the duty cycle is 0%.

Best,

Christine

0 greeneyehawk over 2 years ago in reply to Christine Lambert

Prodigy 30 points

Hi Christine,

It is not possible to set BIDIR_INPUT=1 in closed loop and expect 50% duty cycle to produce no vibration?

Best

0 Christine Lambert over 2 years ago in reply to greeneyehawk

TI__Prodigy 440 points

Sorry, I realized my message was confusing before. Yes, you should be able to have no vibration at 50% duty cycle in closed loop when BIDIR_INPUT=1. Not sure why it is not working.

Can I ask if you have tried to do <50% and it has on vibration?

Best,

Christine

0 greeneyehawk over 2 years ago in reply to Christine Lambert

Prodigy 30 points

From what I can measure, I get no vibration < 48.5% duty cycle. Do you think it is just a tolerance thing, and should I back off my '0' from 50% duty cycle to say 25%?

+1 Christine Lambert over 2 years ago in reply to greeneyehawk

TI__Prodigy 440 points

I would say it probably is likely to be the issue and lowering your duty cycle should give you the results you are looking for.

Best,

Christine

0 greeneyehawk over 2 years ago in reply to Christine Lambert

Prodigy 30 points

Thanks Christine!

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DRV2605L: PWM Driving Open Loop Vs. Closed Loop