LM25037-Q1 - About minimum dead time

Hi Kanemaru-san,

Sorry for the delay in replying to your post let me see if I can find someone to answer you question.

Regards

Peter

Hi Peter-san,

Thank you for your response.

 

I’m looking forward to hearing from you.

 

Regards,

Kanemaru

Hi Kanemaru-san,

I spoke to the engineer in our office who has worked with the LM25037-Q1 and his recommendation is to follow the datasheet. Due to IC variation it may be difficult to guarantee that the minimum deadtime will be 25ns if you use an Rt of 5K. Internal delays may cause the dead-time to increase up to 50ns.

The graph is for typical values only.

Regards

Peter

Please verify this answer if you are happy with it.

Hi Peter-san,

Thank you for your kind support!

I will report this information to our customer.

Regards,

Kanemaru

Hi Peter-san,

 

Thank you always for your kind support.

I have one more question.

 

I understand about your comment.

If we set the dead time in less than 50ns and operate a device, do you have other concern points?

(For example, does not operate normally etc.)

 

>Due to IC variation it may be difficult to guarantee that the minimum dead time will be 25ns if you use an Rt of 5K.

>Internal delays may cause the dead-time to increase up to 50ns.

 

Regards,

Kanemaru

Hi Peter-san,

Would you tell me about the progress on this matter?

I’d greatly appreciate your verification.

Regards,

Kanemaru

Hi Peter-san,

 

I'm sorry for asking your advice so many times.

I have two questions.

 

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[Q1]

Our customer would like to use RT2=4.7kohm(Actual value of dead time is 26ns) and RT1=1.5kohm(Actual value of switching frequency is 763kHz).

Then, we have the following concern.

- Does the internal oscillator stop?

- Does the internal oscillator become unstable?

 

We can’t guess the behavior of internal oscillator from the following block diagram.

Therefore, could you please let us know if you have any information?

 

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[Q2]

Could you please let us know the recommended minimum value of RT2?

I understand that the minimum value of dead time is 50ns.
Therefore, I guess that the minimum value of RT2 is 10kohm.
Is my understanding correct?

---------

 

I’d greatly appreciate your verification.

 

Regards,

Kanemaru

Hi Kanemaru-san,

1. I run a bench test and see the controller can work base on the configuration you given, but this is not guaranteed as there is variation and tolerance between different parts. So the best way is follow recommandation of the datasheet which is verified in producation.

2. Yes, I think your understanding is correct according to the equation (1) in the datasheet.

Thanks
Oliver

Hi Oliver-san,

 

Thank you for your kind support.

I have one more question.

Does the internal oscillator stop at this condition?

I understand that if the dead time of setting is less than 50ns, It may not be able to set the target voltage.

However, they are concerned about oscillator stop.

 

Regards,

Kanemaru

Hi Kanemaru-san,

The oscillator will not stop at this condition base on the bench test.

Thanks
Oliver

Hi Oliver-san,

 

Thank you for your prompt reply.

Our customer would like to know the operating principle(circuit) of the internal oscillator.

Because, They would like to know what kind of side effect there is by making RT2 extremely small.

Could you please let us know it if you have the information of the internal oscillator circuit?

 

Regards,

Kanemaru