MCT8315A: Oscillator Source

Hi Koshi -San,

With Internal clock, speed loop accuracy will be +/-3% across temperature.

About pulse width requirement, I will get back to you by tomorrow.

Thanks and Best Regards

Venkatadri S

Hi Venkatadri-san,

Thank you for your reply to Q2.
I look forward to your reply to Q1.

The customer has another question.

Q3: Is it correct to understand that an external clock with +/- 1% accuracy results in +/- 1% rotational speed accuracy? 

Best Regards,

Koshi Ninomiya

Hi Koshi,

Yes, the speed accuracy is resulting from oscillator error majorly and some sampling errors.

Hence, with good external oscillator we should get better accuracy which is 1%.

I will get back to you about Q1 early next week.

Thanks and Best Regards

Venkatadri S

HI Venkadari-san,

The customer tried to insert a high-precision external clock with a duty of 50%, but the rotation error of about +0.5% did not improve, and it was the same as when an external clock was not used.
Does this mean that this speed error is not a problem of clock accuracy?

Best Regards,

Koshi Ninomiya

Hi Koshi-san,

Venkatadri is currently on business travel, he will answer your queries once he is back next week.

Thanks and regards,

Sachin S

Hi Venkadari-san,

The customer looks forward to your answers to below.
Q1: Is there a specification for the On duty width of the external clock source?
Q3: The customer tried to insert a high-precision external clock with a duty of 50%, but the rotation error of about +0.5% did not improve, and it was the same as when an external clock was not used.
       Does this mean that this speed error is not a problem of clock accuracy?

Best Regards,

Koshi Ninomiya

Hi Koshi-san,

Speed accuracy also depends on the feed back accuracy, BEMF sensing accuracy.

I will reply with more details by early next week.

Thanks and Best Regards

Venkatadri S

Hi Koshi-san,

Q1: Typically, 40% to 60% duty width is sufficient.

Q2: With external clock we can expect up to 1% across temperature.

Thanks and Best Regards

Venkatadri S

Hi Venkadari-san,

The customer understand about the speed loop accuracy when using the internal clock and external clock.
 - With Internal clock, speed loop accuracy will be +/-3% across temperature.
 - With external clock we can expect up to 1% across temperature.

They want to understand one more thing.
Is it correct to understand that if they use FGpin for feedback control, can they expect more accuracy?
Or is the accuracy the saeme as the above with internal or with external even with feedback control?

Best Regards,

Koshi Ninomiya

Hi Koshi-san,

FG is speed indication which is result of clock accuracy.

Thanks and Best Regards

Venkatadri S

Hi Venkadari-san,

The question is whether it is possible to achieve the desired speed by obtaining the speed with the FG pin and applying feedback control to the speed setting.
If the actual rotation speed including an error of +/- 3% (when the internal clock is used) can be obtained with the FG pin, the desired rotation speed can be achieved by changing the rotation speed setting with feedback control.
Is it right?

Best Regards,

Koshi Ninomiya

Hi Koshi-san,

FG feedback can be used to adjust the speed command but error factor can vary with conditions.

Host can control duty cycle based on the feed back.

Thanks and Best regards

Venkatadri S

Hi Venkadari-san,

Thank you for your support.
The customer understands, and they are proceeding the evaluation of the MCT8315A in their system.

Best Regards,

Koshi Ninomiya