DRV8824: Part is missing step commands at 2.3 us pulse widths.

James Sullivan73

Prodigy 185 points

Part Number: DRV8824

I see the part missing step commands.

This occurs as early as 2.3 us through 2.7 us pulse widths.

This occurs at a frequency of 16 Khz. or 50 Khz.

A motor does not have to be attached - hence no switching noise from the chopper.

I see it by looking at the "Home" position output -

It will regularly output a home pulse that is too long. - missing one or two consecutive pulses.

Can someone explain this timing limitation ?

The spec says 1.9 us.

over 4 years ago

0 Wang5577 over 4 years ago

TI__Guru 56650 points

James,

Would you show me the STEP vs nHome waveform between a normal STEP pulse and the abnormal STEP pulse?

It can speed up the debugging process. Thanks,

0 James Sullivan73 over 4 years ago in reply to Wang5577

Prodigy 185 points

I can cause the problem by shortening the pulse width.

Good. OR...

Bad.

Good:

0 Wang5577 over 4 years ago in reply to James Sullivan73

TI__Guru 56650 points

James,

Thank you for your test waveform. I am going to check it with our design team. Since this device was released ten years ago, it may take some to debug or simulate it.

BTW, do you test it on an EVM or your board? I just want to make sure there is no any filter or series resistor on the STEP pin. So, STEP pin can get that waveform's sharp rising/falling edge.

0 James Sullivan73 over 4 years ago in reply to Wang5577

Prodigy 185 points

Hello,

No resistor.

when I make the pulse longer - it works.

This makes the part out of spec.

Just looking for why this might be true.

.js.

0 Wang5577 over 4 years ago in reply to James Sullivan73

TI__Guru 56650 points

James,

I just submitted a request to ask design team to check this parameter. After I have the result, it will be shared in this e2e thread.

0 Wang5577 over 4 years ago in reply to Wang5577

TI__Guru 56650 points

James,

Our designer will check it next Tuesday. Let me close it temporary and re-open it when I get the answer.

0 Wang5577 over 4 years ago in reply to Wang5577

TI__Guru 56650 points

James,

Design team checked the internal clock at Analog level and the preliminary result close to your test result. To get the final result, we need a further investigation with digital simulation.

I will reopen the post and share the final result with you as soon as possible.

0 Wang5577 over 4 years ago in reply to Wang5577

TI__Guru 56650 points

James,

After check the internal circuit, we find the device supports 4.6us minimum tWH(STEP) (STEP pin high).

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DRV8824: Part is missing step commands at 2.3 us pulse widths.